Astrology
The art of judging the influence of planets and stars on human beings—in the past, in the present, and, by extrapolation, in the future.
India and China have had astrological systems for a long time. These are highly developed, and regarded with respect. The Western version has its ancestry in Babylonia, where astronomers were listing constellations and prominent stars in the second millennium b.c. With the passage of time, they came to distinguish seven “planets,” counting the five true ones visible without telescopes plus the Sun and Moon—in other words, the seven bodies that were not fixed like stars. All seven were associated with divine beings. They were seen to travel through sections of the sky that astronomers defined by twelve constellations, the signs of the Zodiac.
In the sixth century b.c., Babylonians developed a theory that these celestial orbs influenced the world below. Greek advances in astronomy presently refined the possibilities, and the Western form of astrology took shape. Earth was located at the center of the universe, with seven transparent spheres rotating around it, one outside another, each carrying a planet. The Moon’s was nearest to Earth; concentrically outside it, in order, came the spheres carrying Mercury, Venus, the Sun, Mars, Jupiter, and Saturn. Outside Saturn’s sphere was a larger one bearing the stars, and outside that was an even larger one that imparted motion inward to all the others. The planets exerted influence on the world at the center, and, in their varying relations to the Zodiac and each other, were “interpreters” of destiny. As in Babylonia, deities were associated with them. “Mercury,” “Venus” and the rest are the Roman names of the divinities that were assigned to these planets by classical astrologers because they were thought to be the appropriate ones. The fifth planet’s influence, for example, tended towards strength, assertiveness, and anger, so it was taken to be the planet of the war god Mars.
Astronomically, the system is no longer viable, and astrologers are quite aware of the fact. But they still tacitly assume it, in its essentials, as a kind of operating fiction, its use justified by results. In practice—supposedly—it does work. A horoscope can be drawn up on the basis of the planets’ positions at someone’s birth. The most important is the Sun, which is in Aries (the Ram) during part of March and part of April, then in Taurus (the Bull) during the rest of April and part of May, and so on. The date of birth determines the person’s Sun-sign or birth-sign: Aries, for instance, if the Sun was in that portion of the sky at the time, Taurus if it was in the next portion, and so on. The Sun-sign is said to have a crucial bearing on the personality.
Complex calculations about the positions of the other six planets—sometimes, today, computerized—can be expressed on a birth-chart, and add further insights into the individual’s character and destiny. On the basis of the inferred destiny and perhaps also of the planets’ foreseeable positions at some future time, events yet to come can be predicted; or, at any rate, probabilities—the celestial bodies, to quote an astrologer,“influence but do not compel.” Auspicious and inauspicious days can be identified in advance for some
important action. The technique is not confined to individuals. It can be applied to cities, states, institutions, or whatever, preferably at the time of their foundation, the equivalent of birth. Projections into the future can be made similarly. A horoscope of the city of Liverpool, in England, is said to have shown that it will become the capital of England in the twenty-third century—an extreme case but not inconsistent with the logic of the system.
An astrologer casting a client’s horoscope in 1617. The progress of astronomy was beginning to raise doubts about astrology, but astrologers were still being consulted.
(Ann Ronan Picture Library)
To revert to history, Romans were hesitant about embracing this production of Greek cleverness, but early in the Christian era, it was growing popular at high social levels, and the casting of a horoscope at a child’s birth was becoming customary. An astrologer named Thrasyllus was an adviser to the emperor Tiberius. When some of his predictions failed, Tiberius lost patience and was about to push him off a cliff, but he managed to make a good one just in time.
After the Roman Empire became officially Christian in the fourth century, astrology began to be frowned upon. Augustine, the most influential of the Church fathers, offered rational arguments against it and argued that even when astrologers got predictions right, this was probably due to inspiration by evil spirits. For a long time, it was in disfavor. However, it began to come back in the early Middle Ages as a quasi-scientific technique. Planets could no longer be gods, but in some mysterious way, they might still play a part in earthly affairs. Scholars in the Church kept it off the list of forbidden arts, and Saint Thomas Aquinas, the leading medieval philosopher, allowed it a strictly limited validity. Its practitioners worked freely, though they stressed character reading and medical diagnosis rather then prediction. It became very popular in the sixteenth-century Renaissance. John Dee, in England, was allowed to draw up horoscopes for royalty and to set a date for Elizabeth I’s coronation. Nostradamus, in France, published hundreds of prophecies, some of them remarkable, though for him, astrology seems to have been subordinate to another method of forecasting that remains obscure.
The waning of Earth-centered astronomy was naturally adverse to astrology, and it declined again, but it never expired, and eventually, it began to recover. It could be rationalized, as it still can, by the argument that it reads the heavens as they appear to be, and no astronomical proof of what they actually are can make any difference. Its Western revival had its origin in Theosophy. Helena Petrovna Blavatsky, the founder of the movement, endorsed it in her book Isis Unveiled, published in 1877. One of her followers, writing under the name Alan Leo, was its first popularizer and produced a handbook entitled Astrology for All. In England, France, and the United States, interest gradually revived. However, it was only in Germany that astrology became a serious field of study, thanks partly to another Theosophist, Hugo Vollrath. The suffdrings of Germans in the great inflation of 1923–1924 and in the ensuing years of mass unemployment contributed to a longing for a doctrine that would make sense of events and perhaps foreshadow a better time ahead. An Astrological Congress in Munich was the first of a series. Germans of academic standing tried to make astrology an authentic system.
During this interwar period, astrology also enjoyed a vogue on radio and in newspapers. Exponents in English-speaking countries, such as Evangeline Adams and R. H. Naylor, made forecasts on topics of public interest. However, their occasional successes were outweighed by numerous failures. Later in the twentieth century, while astrology of a sort still flourished in the press, it was more cautious and largely confined to minihoroscopes for the day (or week or month) giving vague advice to readers born under each sign and avoiding specific detail about the future. In 1967, a well-informed writer on astrology, Ellic Howe, pronounced, in the light of his own negative findings, that prediction was its “Achilles’ heel.”
The astrology of a more responsible kind that continues to be practiced is concerned chiefly with character and destiny. Howe’s adverse verdict on prediction might be allowed to stand if it were not for an exceptional case history, that of Germany under the Nazi regime, from 1933 on. Seemingly, the activities of Vollrath and other enthusiasts showed predictive results that cannot be dismissed. Someone had cast the horoscope of the German republic on the basis of the date of its proclamation in 1918, and several attempts had been made to cast Hitler’s. There is evidence—some of it indisputable, some of it circumstantial but good—for correct long-range forecasts of Hitler’s career and the fortunes of Germany in World War II and its aftermath. Hitler, it was foretold, would be triumphant at first, and Germany would be victorious for two years, but in 1941, the tide would begin to turn. There would be major disasters in 1943 and a cataclysmic end, including the Führer’s downfall, in 1945, though a recovery would be under way after three years of peace. All of this was right. Hitler did not believe in astrology, but his awareness of its prediction for 1941 as a threat to morale was shown by a clampdown on astrologers in June of that year.
The German successes raise a problem. Can astrology predict after all? If so, how to make sense of these facts? Whatever astrologers may say in defense of their art, it remains the case that the universe is not what it looks like from below. They have done their best to fit in the three planets added to the traditional seven, but much more is involved than that. The crystal spheres and their resident deities have gone. Mercury, Venus, Mars, Jupiter, and Saturn, together with the three latecomers, are barren globes moving through a void at vast distances from Earth and from each other. Medieval astronomy recognized greater distances than is commonly thought, but came nowhere near the remoteness of the stars, which are not only remote but in spatial relationships to each other that have nothing to do with the Zodiac: its constellations would disappear for an observer from a different vantage point.
An astrologer today might speak of correlations or synchronisms rather than influences. If such a claim were borne out by results, it would deserve to be investigated, but results are lacking. The German phenomenon may be thought to hint at some quite separate factor. The same could be said of the rare but documented triumphs of character reading by horoscope (or ostensibly by horoscope), such as one recorded at the University of Freiburg, where an astrologer named Walter Boer diagnosed the problems of a juvenile delinquent unknown to him in virtually the same way as a team of psychologists. Ellic Howe, who draws attention to this case, takes the view that such successes are not really produced by the subject’s birth-chart as such but by a kind of intuition making use of it, which few would-be astrologers are capable of. Jung, as is well known, took an interest in astrology, but he used patients’ horoscopes chiefly as therapeutic aids rather than sources of information.
One quasi-astrological finding has stood up to scrutiny, often very hostile. In 1955, a French statistician, Michel Gauquelin, proved that a significant number of people with certain abilities were born when certain planets were either just clearing the horizon or at the apex of their passage across the sky. Many outstanding athletes, for instance, were born when Mars was either rising or “culminating.” Jupiter seemed to be connected with famous actors in the same way. The ironic fact is that Gauquelin’s correlations are totally unrelated to traditional astrology, for which he found no support whatever.
Thursday, January 31, 2008
Astrology
Sunday, January 27, 2008
Doesn't Have A Clue
This is a real life story, so bear with me as I give somebackground information.We have a "free ad" section at our web site where people canplace a free ad for their business. Ads are submitted weekly andpublished on the web. Now, to place an ad, someone has to visitour web site and fill out a form containing their email addressand the copy of the ad. We try to make it as easy as possible,but the bottom line is many people are not serious, and don'thave a clue as to how to run a business on the web.When the ads are received, we send an automatic response to theperson who sent it. Perhaps one out of ten has an incorrectemail address and the response is returned as undeliverable.What a waste of time.How do these people think that people can respond to their ad iftheir email address is incorrect?Going through our archives, I found some real gems - what do youthink about these offers?"Join our MLM and earn beg income". This is either a typo orthey are promising very little in the way of earnings. Thisperson obviously didn't proof their copy before submitting thead.Another ad promised huge earnings, but gave no contactinformation. Not a web site URL or an email address to befound. Guess they figure it is so powerful an offer, we willfind them - another waste of time."Make Money! Turn $10 into $40,000 CASH like I did" - but wait -this guy is using a free email account. If he's making all thatmoney, wouldn't you think he could afford one for ten bucks amonth - maybe he is saving all those $10 bills so he can earn$40,000 CASH with each one."You can make 500% Profit without investing any money" - need Isay more!"Tired of the "Rat Race"? Free online training and no capitolneeded!" Did this guy mean "capital"? I'll hang on every wordhe has to say."Exciting,EasyandProfitable" - guess this person never learnedhow to use that big bar on the bottom of the keyboard. I thinkyou see where this article is going.If you are going to advertise a business on the web, and youpresent less than a professional image - you're not going to dobusiness. If you present yourself like the above examples, enjoyyour "walk on the quiet side". Most people are not idiots, andI'm sure the authors of the above ads are not either. But whygive that impression? I sure wouldn't do business with any oneof them.I read another ad for Web Design and the HTML coding in his adwas wrong. That sure built a lot of confidence.Most people scan poorly constructed ads and simply "click away".Guess they feel like I do. If you don't care enough to write acredible ad, why should I think you'll care about me if I buyfrom you?Many people rely too heavily on the spell checker on theircomputer. This is a mistake. After you do spell check, getsomeone else to read it. When writing something, many times youget so close to the article, you miss mistakes that someone elsewould quickly find. Many words that are being used incorrectlywill pass spell check.Remember - you usually only get one "shot" when a person seesyour ad. If it is well written, and has an attention gettingheadline, you just might make that sale. If you want to dobusiness on the web, get serious or people will come to theconclusion that you are someone who "Doesn't Have a Clue" andlook elsewhere.
Test, Test and Re-test
We could all take a lesson from children. As they are growingup, and learning right from wrong, they are constantly testing tosee what they can do, and what is not acceptable.I see hundreds of ads everyday on the web, and while there aresome good ones, most fall into the "ho-hum" variety, and some aredownright awful. Now this isn't bad, if they are testing to seewhat is going to work, and what isn't.Many put up an ad with no idea as to whether it will produce ornot. They let the same ad run for a period of time, and wonderwhy they didn't get results. They then do one of two things.They either blame the publication for not generating business forthem, or give up entirely and go out of business. Others will runan ad once, and when the world doesn't beat a path to their door,they react the same way.It is a proven fact that an ad must be seen five to seven timesbefore someone can be expected to take action. If your ad istargeted to your market, and you are not getting responses, theodds are you have a "crummy ad". It is not then time to quit orblame the publication. It is time to change the ad.All successful marketers have one thing in common. They areconstantly testing the effectiveness of their ads. One of themost successful that I know, almost always runs more than one adin the same or similar publication at the same time. You couldput the ads side by side, and not realize they were from the sameperson for the same thing. She lets each ad run five times,always keeping careful track of the drawing power of the ads, andkeeps the strongest and changes the weakest.Mechanically, her method is really quite simple. She uses adifferent email address in each ad, and a different websiteaddress as well. Both websites are exactly the same, but havedifferent URL's. She got her websites from a low cost web spaceprovider where she not only reserved the name of her site, butgot web space as well for less than the cost of her ads. Thereare several low cost web space providers. I can recommend
The Trap
ot a day goes by that I don't hear about someone lamenting their decision to leave corporate America and work at home.Maybe they were laid off, opted for early retirement, or justdecided that commuting four hours on the train, coupled with aneight hour workday was simply too much. Possibly, they will keeptheir job and work part-time at home to earn extra income. Whoknows what the reasons are, but that is not important.With "visions of sugarplums" dancing in their head, they decidedto start their own home business. They believed the ads aboutworking in their pajamas when the spirit moved them, and after amonth or so woke up to reality. They weren't making a dime.Where did they go wrong? Well, when they worked for someoneelse, they were expected to be at work at a certain time everyday. Depending on the business, there was a certain dress code,and they had goals to meet. Granted, these goals were usuallydetermined by someone else, but they were the ones who had tomeet them.It is easy to work for someone else, as they are the ones callingthe shots. They actually lived under an umbrella of discipline.Granted it was someone else's umbrella, and maybe they didn'trealize this. Possibly they did, and that was the reason theydecided to work on their own.One of the most common problems behind the failure of a homebusiness, is the lack of discipline. Some think they can workwhen (and if) they want to, and their mailbox will "overfloweth"with twenty dollar bills. Well, I got news for you!Running your own business, whether it is a brick and mortarestablishment, or a home business, requires work. It usuallyrequires more effort than if you worked for someone else. Youwill also have to do some things you don't enjoy. But, if youare the chief (or only) "honcho", you had better be able tohandle all facets of your business.So, how do you go about working at home? First and foremost, youhave to have a regular schedule and adhere to it. This isespecially true if you expect people to contact you by phone. Ifpeople try to call you, and don't get an answer, they quicklymove on. You have to be available during normal business hours.If you are in an online business, this is usually from 9:00 AM to8:00 PM. Yes there are three time zones in the USA. If you liveon the east coast like I do, when you are getting ready to packit in for the day, folks on the west coast may just be returningfrom lunch.If you are not tied to a telephone, it is still important tomaintain regular hours. More importantly, you should have dailygoals. If you meet those goals, the rest of the day is yours.But many people always think there is tomorrow.For far too many, tomorrow never comes, and things that shouldhave been done aren't. Maybe when the kids are at school willwork for you, or possibly late at night. You might even have topass up on your favorite "soap". Don't deal with hours - you'renot being paid by the hour - deal with goal oriented results.Working in your pajamas sounds great, and many of the offers youmay hear state that you can. If I get an idea in the wee hours,I may hop on the computer dressed like that, but for normalbusiness hours that is simply a myth. Who wants to spend theirlife like that?You must have an effective work space, which is free ofdistractions. You should have quiet office space in your house,which is out-of-the-way, and off limits during your work hours.Treat this like an office. Keep it neat. While I am not theneatest person in the world, I do know where everything is. If Iget a call from a client, I'm not fumbling about looking for theinformation I need. A filing cabinet next to your desk goes along way.When you get an email, take appropriate action the same day, thenfile it in a place where you can find it. Delete all emails inyour "in-basket" older than 30 days. If they're older than 30days, they're not worth anything anyway.If you don't fall into the "trap", which many folks do, you justmight make it in your own home business.
FIVE FANTASTIC WAYS TO PROMOTE YOUR AFFILIATE PROGRAM
If you belong to any affiliate program, you know that beingsuccessful at the affiliate game hinges on one simple concept:getting as many people to join as you possibly can.There are a lot of different programs out there and even moreways promote them, so I've narrowed things down to what I believeare the five absolute best ways to get the word out about YOURaffiliate program. So, without further ado, here they are:1) ON EVERY PAGE OF YOUR WEB SITEThat's right... every page. After looking through your site andseeing that link on every page, they're just bound to click on atleast one of them. Promoting your program on every page will notonly utilize the proven marketing method of repetition, but willalso display your enthusiasm, which is also a great tool.2) IN YOUR NEWSLETTERSince most of your core customers are already looking at it, yournewsletter is a terrific place to promote your affiliate program.Position an ad with a link right at the top of your newsletter,again somewhere in the middle, and also at the bottom.3) EZINE ADSEzines like DEMC and AIM have huge numbers of subscribers, andboth cater mostly to an audience of online businesspeople andopportunity seekers. Therefore, ads placed in these newsletterscan reach literally tens of thousands of the right kind ofpeople. Reaching a targeted audience like this is key if youwant a good return on your investment.4) PRESS RELEASESIf your affiliate program is new, unique, or especiallyprofitable, a press release sent to the right audience can reallygive you a boost. A well-written press release just placed onyour web site can give your program a "newsy" feel that mightreally impress people.5) WORD OF MOUTHI can't say enough about word-of-mouth advertising. If you'reexcited about your affiliate program, talk about it. Tell yourfriends, your family, your co-workers, and people on the bus allabout how you're making money. People who know you are morelikely to take you on your word, and if they tell their friendsand family... you get the picture.Promoting your affiliate program really isn't very hard, and itcan make the difference between success and failure. Use thesemethods, and you're likely to go far.
Make This One Change To Your Web Page... and Double and Triple Your Profits
Are you getting visitors to your web site but nobody wants tobuy? Do people come to your site once, but never return? I'vegot a simple change you can make to your opening web page thatcan quickly turn your luck around.By far the biggest reason most web sites don't sell as much asthey could is due to a single problem. The words on theiropening page don't do their job.On the Web, you only get a few seconds to grab new visitors andkeep them. If the wording on your opening page is falling downon the job, no one will stick around long enough to buy. Yoursite is finished before it even gets started.Over and over again, everywhere I go on the Web, I see sites thatare shooting themselves in the foot. The opening page has toolittle information to hold a visitor. Or the opening page hasplenty of information, but it is too hard to make heads or tailsof. Or the opening page has too much information, so much thatnew visitors get lost.Given the few seconds visitors spend on a new site, they justdon't have time to carefully study a site's copy to figure outwhat the owner intends for them. Your copy needs to IMMEDIATELYhit visitors squarely between the eyes.Here's how to do it.Distill what you have to offer down to your most popular andpowerful product or service. Don't throw a whole selection ofproducts at new visitors. Just give them one good one they cansink their teeth into.Next figure out the one most powerful advantage your product orservice gives customers. Also think about what kinds of visitorsare most likely to buy. Once you have these two things in mind,you're ready change your copy so it grabs visitors and makes thembuy.Give Your Page a Headline.Start your page with a headline in big type. Begin your sentencewith an action word. Look at the title of this article. "Makethis one change to your web page and double and triple yourprofits."I don't say "here are 27 ways," I just promise you one. Then Igive you a powerful benefit this change can bring. Do you wantto double and triple your profits? Absolutely. Most peoplecontinue to read the article.The same principle works for your opening web page. A big, fat,exciting headline is quick and easy to read. It pulls peopleinto the copy that follows it.Feel The Reader's Pain.People only buy when they feel you can solve a problem that iscausing them pain. People want to save money, save time, get alife, feel sexier, and more.Don't follow your headline with a diatribe on how good yourproduct is. Instead, talk about the thing readers care aboutmost. Make your copy describe a problem the reader has. Tellhow the problem affects the reader's life. Show the reader howthe problem will get worse, much worse, over time if it is notfixed.Now Dole Out The Medicine.Present your product or service as the solution to the customer'sproblem. Describe its most important features, then connectthem with the benefits they will bring.Most of your customers don't automatically understand how yourproduct's great features can help them. You have to describe thebenefits. It helps to give real life examples of how the featurehelps people.Try not to bury your reader in features. If you have more thanthree, list them in bulleted form. Bullets help readers digest abatch of related points.Trot Out The Raves.Next is a good time to add several enthusiastic testimonials fromsatisfied customers. Have the customer talk about how she gotthe results you promised in your benefits section.If your product will save the customer time and hassles, have areal life customer talk about how he now has time to go to hisson's baseball games...now that he can get work finished faster.If your product or service is new, have several people try it,then give you their comments. Most people are delighted to help,especially if they know you will be publishing their opinions.Tell Them HOW TO BUY.This is the one thing so many sites miss. Give people a bigorder button they can't miss. Make it easy for them to buy.Easy ordering should include information on how customers cancontact you. Include your email address (which you check often),your phone number, and your physical location. Also include yourguarantee if you have one.Let customers know how long it will take for you to deliver theproduct or service. And be sure to tell them how much extrashipping and handling will cost. Stating these things right upfront helps customers make a decision to buy, NOW.Make these changes to your opening web page today. Thisimprovement is the one thing that can turn your sales aroundimmediately. I've seen sites double and triple their sales afterwe put this changes in place. One man called to say his saleswent up "ten fold" within a couple of days.
About the Author
Give Your Affiliate Program A Lift With A New Or Improved Product
If an affiliate program is an important part of your business,your profits are only as good as your affiliate members. Salesdrop like a rock when they get discouraged or lose interest.You will see the dreaded signs if you frequently visit youraffiliates' sites. The banner or enthusiastic endorsement theyonce had on their opening page is now relegated to a link on thesecond or third tier of their site. Something as simple as thatcan cut the number of hits you get by a factor of ten or twenty.Two things usually account for members giving you the back burnertreatment: Your product or service isn't selling as well as itonce did for them. Or members are simply losing interest becausenewer, more exciting affiliate programs are grabbing theirattention.You can immediately solve both problems by offering a new orimproved product or service. Spend time to make sure your newproduct is a big improvement over what has come before. The moreyou can insure your product is a big deal, the more excited youraffiliates will get.Make your roll-out a big production. Give your new creation awhole new area with a fresh new look on your web site.Two weeks before you unveil your new product, start sendingannouncements to your affiliates. Let them know somethingimportant is about to happen and they will be the first to hearabout it.After you bring out your product, do a quick follow-up withmembers. Get comments on how they expect the new product tosell. Harvest early accounts of how some members are doing wellwith the product. Include these comments in your weekly emailupdates to members.A word of warning--try not to veer completely away from what hasworked for you before. If you have always sold software, don'tbring in a new line of office furniture as your new product foraffiliates. An exciting new software application will workbetter and will not dilute the brand identity your business hasenjoyed.Got a major product you don't want to ignore? Good! It'salmost always easier to get affiliates and customers excitedabout an improvement to an old favorite than it is to make afavorite out of a completely new product.Keep a file of customer complaints and ideas about your product.Over time you can use these as ideas starters for ways to buildimprovements that customers and affiliates will appreciate andvalue.When interest in your product or service starts to diminish, pullour your file and make requested improvements. Add in enoughimprovements and you have a new issue, a next generation, or afresh edition you can sell as a replacement or upgrade to yourlong list of previous customers.Affiliate programs are still the number one way to market on theWeb. It pays to keep your program exiting and top-of-mind. Formany companies, it is unlikely that a better way to boost profitswill come along any time soon.
REVISITING THE 'BENEFITS' FACTOR
If you are in the business of making sales (as mostonline marketers are, in one form or another) then youknow that it is a basic tenet that you must appeal toone of people's basic NEEDS if they are going topurchase your product or service.So what are those basic needs, anyway?Well, the most obvious needs are for shelter, food andwarmth. But there's a different kind of 'warmth' thatmany people need, too, and that's where you come in.People need to feel needed, or they need to have comforts,or they need to have their problems solved, or they needto BELONG - these are all needs for a different kind of'warmth' that we can appeal to in our sales campaigns,in our advertising materials, and on our websites.The bottom line is that potential customers are onlyinterested in what your product or service can do forthem - what NEED your offering will fill. Period. So youcan try to convince them that your widget is prettierthan someone else's widget, or faster, or whatever...but only if that can be shown to benefit them.I'm not talking about features, here. There's a bigdifference between 'features' and 'benefits'. A bettermousetrap might have the 'feature' of a more reliablespring-loaded mechanism - but that makes it a bettermousetrap because it has the 'benefit' of being ableto get rid of more mice! See the difference?We've all heard the phrase 'to keep up with the Joneses.'Ad agencies have long used our need to belong, to fit in,to be a 'part of' rather than apart from, to sell us onvarious products or services. You can take advantage ofthis human drive to sell your offering, too.The important thing, then, is to make a point of addressingthe benefits right up front. On the front page of yourwebsite, or in big letters on your ad copy, make sure youtell the reader 'what's in it for them' if they purchaseyour product or service. Which basic human need will itmeet? Figure that out first, and the whole rest of yourmarketing campaign will come so much easier to you.If you can discover what 'problem' your product or serviceis the answer to, then you're on your way to success. Willyour product make your customers sexier, allow them moreleisure time, make them lots of money..? Will it give themone of the many kinds of 'warmth' that we all crave?Make sure you say so, loud and clear, and prospectivecustomers will be sure to hear you!
REVISITING THE 'BENEFITS' FACTOR
If you are in the business of making sales (as mostonline marketers are, in one form or another) then youknow that it is a basic tenet that you must appeal toone of people's basic NEEDS if they are going topurchase your product or service.So what are those basic needs, anyway?Well, the most obvious needs are for shelter, food andwarmth. But there's a different kind of 'warmth' thatmany people need, too, and that's where you come in.People need to feel needed, or they need to have comforts,or they need to have their problems solved, or they needto BELONG - these are all needs for a different kind of'warmth' that we can appeal to in our sales campaigns,in our advertising materials, and on our websites.The bottom line is that potential customers are onlyinterested in what your product or service can do forthem - what NEED your offering will fill. Period. So youcan try to convince them that your widget is prettierthan someone else's widget, or faster, or whatever...but only if that can be shown to benefit them.I'm not talking about features, here. There's a bigdifference between 'features' and 'benefits'. A bettermousetrap might have the 'feature' of a more reliablespring-loaded mechanism - but that makes it a bettermousetrap because it has the 'benefit' of being ableto get rid of more mice! See the difference?We've all heard the phrase 'to keep up with the Joneses.'Ad agencies have long used our need to belong, to fit in,to be a 'part of' rather than apart from, to sell us onvarious products or services. You can take advantage ofthis human drive to sell your offering, too.The important thing, then, is to make a point of addressingthe benefits right up front. On the front page of yourwebsite, or in big letters on your ad copy, make sure youtell the reader 'what's in it for them' if they purchaseyour product or service. Which basic human need will itmeet? Figure that out first, and the whole rest of yourmarketing campaign will come so much easier to you.If you can discover what 'problem' your product or serviceis the answer to, then you're on your way to success. Willyour product make your customers sexier, allow them moreleisure time, make them lots of money..? Will it give themone of the many kinds of 'warmth' that we all crave?Make sure you say so, loud and clear, and prospectivecustomers will be sure to hear you!
REVISITING THE 'BENEFITS' FACTOR
If you are in the business of making sales (as mostonline marketers are, in one form or another) then youknow that it is a basic tenet that you must appeal toone of people's basic NEEDS if they are going topurchase your product or service.So what are those basic needs, anyway?Well, the most obvious needs are for shelter, food andwarmth. But there's a different kind of 'warmth' thatmany people need, too, and that's where you come in.People need to feel needed, or they need to have comforts,or they need to have their problems solved, or they needto BELONG - these are all needs for a different kind of'warmth' that we can appeal to in our sales campaigns,in our advertising materials, and on our websites.The bottom line is that potential customers are onlyinterested in what your product or service can do forthem - what NEED your offering will fill. Period. So youcan try to convince them that your widget is prettierthan someone else's widget, or faster, or whatever...but only if that can be shown to benefit them.I'm not talking about features, here. There's a bigdifference between 'features' and 'benefits'. A bettermousetrap might have the 'feature' of a more reliablespring-loaded mechanism - but that makes it a bettermousetrap because it has the 'benefit' of being ableto get rid of more mice! See the difference?We've all heard the phrase 'to keep up with the Joneses.'Ad agencies have long used our need to belong, to fit in,to be a 'part of' rather than apart from, to sell us onvarious products or services. You can take advantage ofthis human drive to sell your offering, too.The important thing, then, is to make a point of addressingthe benefits right up front. On the front page of yourwebsite, or in big letters on your ad copy, make sure youtell the reader 'what's in it for them' if they purchaseyour product or service. Which basic human need will itmeet? Figure that out first, and the whole rest of yourmarketing campaign will come so much easier to you.If you can discover what 'problem' your product or serviceis the answer to, then you're on your way to success. Willyour product make your customers sexier, allow them moreleisure time, make them lots of money..? Will it give themone of the many kinds of 'warmth' that we all crave?Make sure you say so, loud and clear, and prospectivecustomers will be sure to hear you!
YOU CAN DO THE WORK OF 100 PEOPLE!
It's an old cliche - "Give a man a fish, feed him for a day.Teach him to fish, feed him for a lifetime."That's been true forever. But, there's a new game in town andtheir motto goes like this - "Sell a man a fish, earn 10 bucks,feed yourself a happy meal. Teach a man to fish, take part ofevery catch, and HE will feed YOU for a lifetime."They're trying to tell you that the secret to business success ismultiplication - if you can find something that's profitable, doit over and over again, and you will get paid each time you doit.But if you can multiply your efforts by creating a group ofpeople who are doing your something, and if they pay you (just alittle bit) for each something, you get paid 5, 50, 500 timesmore rewards.That's the key to financial security and the freedom to do whatyou want in life - multiplying your efforts.Everybody's heard of the old fashioned way - multi-levelmarketing - where you sign up, then you sign up your friends andthey sign up their friends, and on and on. Problem is, you runout of friends VERY fast, because everyone in your group knowsmany of the same people. In addition, doing both the teaching andpromotion of the business takes up too much of your time andmoney.With the advent of the world wide web, you can now increase thatpool of potential recruits to include everyone on the net -hundreds of millions of people! And the best part is, thepromotion and teaching can be automated by computers.It's called "remote control selling" and it's the biggestopportunity to hit the world since the telephone gave us instantvoice to voice contact. Many companies now have networks that aretrue turnkey systems.That means you get everything you need, like one-stop shopping atthe supermarket. As an affiliate, you can take advantage of allof all the company's resources: banner ads; classified ads; yourown website; a library of articles, training materials, salesletters, and much, much more. Once a proven way to recruit andteach a prospect into successful affiliates is found, let thecompany do the work for you, automatically. You just sign on,turn the key on the system and refer prospects to it!An additional benefit is that getting prospects will becomeeasier because they will trust you because YOU have the image,prestige and resources of the major player behind you.Choose carefully-look over the websites of several companies.Sign up for one that offers a free trial period. Make an informeddecision about the program. Then, be prepared to work. Turn onthe keys and find the prospects and the system will take care ofthe rest.A real network marketing opportunity is NOT a get-rich-quickscheme. It isn't free. If you want the system to work for you,then put in the effort, cultivate prospects, bring people intoyour group and help them to be successful. Can you find 100people that want a new, better life? Yes, and you'll be glad youdid. You take chances every day - stop taking chances that rewardothers, and take a chance on yourself!
THE "MISSING LINK" OF THE INTERNET
Networking is a powerful tool.Just to be clear, we are NOT talking about running miles ofcable from one computer to the next and we are NOT talkingabout recruiting people for a business opportunity. What we ARE talking about is recognizing, developing and profiting fromyour NETWORK of contacts, no matter what business you are in.We all know more people than we think we do. Surveys haveshown that, by the time we graduate college, most of us knowabout 250 other people. The Internet has changed all of that.That number goes way up when you think of people you know viathe Internet. Let's look at five ways to develop your networkof contacts, online and offline, to help skyrocket your business,no matter what that business is. Make a list of the people youknow and let's get ready to go!STEP 1:The first step is to let your group of contacts know whatyou are doing. Honesty is the key here. HELP them see thenext level of relationship where you can be of help to eachother in a business setting. If they are going to open theircontacts to you, and you to them, you must both be comfortable.And don't push it. If they hesitate, back off.STEP 2:Ask them how you can help them. Many times in life and businesswe get by giving. HONESTLY offering your help to them withoutasking anything in return will set the stage for a mutuallybeneficial relationship. Honesty is the key. If you have lessthan noble motives, stay away.STEP 3:Be involved on the Net. The most efficient way to make newcontacts is over the Internet. There are thousands of chats,newsgroups and forums out there. Almost certainly there aresome on YOUR topic. Get in the swim and meet new people.STEP 4:Develop credibility. Here we go giving before we get again.While in the chats and on the forums answer EVERY questionthat you can. Don't answer if you don't know. But if you DOknow, make your voice heard often. Be sure and let them knowhow to reach you and, over time, they will.STEP 5:Be in for the long haul. If you are not building relationshipsfor the long haul, people will sense that and back away. Letpeople know that even though many things may change over theyears, you won't.If you begin with these five basics you will start to developyour own network of contacts that, over time, will mean youmay NEVER HAVE TO FIND PROSPECTS AGAIN. The math isstraightforward. Each contact you develop who shares even oneperson with you is opening you up to not 1, but 250 otherpotential prospects.Remember to be honest and up front about your intentions andYOUR network of contacts will grow up to produce a bumper crop.
SMART TAGS? WHO SAYS THEY'RE SMART?
Microsoft has said a lot about Smart Tags. And it isMicrosoft who claims this is a "smart" idea.I'm not a fan of Microsoft products. Still, there are realbenefits to all software developers and PC users in theuniformity from system to system that Windows provides. But ifMicrosoft makes this move, it's a step too far. Here's whatSmart Tags will do.> Advertisers will agree to pay a fixed amount for a click on a keyword. As at GoTo.Com, keyword "ownership" is subject to a higher bid.> Website pages downloaded from any website to any computerusing Windows will be scanned for these keywords.> Those found will be highlighted and converted to links to the advertiser's site.I've heard talk of Smart Tags for some time. There has beenan awesome hue and cry of opposition. I was glad Microsoftresponded by deciding against including this "feature" in theirnew XP operating system.Then The Other Shoe DroppedSomething just as "good" as Smart Tags is already here. Andit's ugly. Here's a quote from "The San Francisco Chronicle.""TOPtext is an example of 'contextual advertising,' thelatest attempt by online advertisers to reach the eyes and mindsof Web surfers. TOPtext turns existing words on a Web page intohyperlinks that redirect a computer user to the advertiser'ssite." (The full article is available at either of the followinglinks. Erase the spaces and returns in the first one beforepasting.)
About the Author
DO NUMBERS HELP?
Demographics about the Web abound. You may find such datahelpful. In general, when I look at the research available, Iget a feeling it's incomplete. The Web is so vast, I don't thinkit's possible to find a small representative sample from whichsignificant results can be obtained that reflect the whole. Inthe end, what is reported with numbers may not matter to you, even though the source is impeccable.Numbers Don't Always WorkFor example, it has been reported that 330 million people are"on the Web." I have not read closely enough to know if thismeans daily, occasionally, or somewhere in between. To me itdoesn't matter.Even if this number were doubled, it would still mean nothingto me. I am interested in reaching an extremely small fractionof web users. The implication I've been seeing in spam messagesof late is that I can reach all 330 million people. This is alie. But there would be no gain in trying to do so in any case.Honest Numbers Can Be WrongI recently read a report that of nearly 100,000 spam messagesreceived by one firm, about a third were promoting po-rn sites. (I used a hyphen in hopes of ducking blocking software.) Whatdoes this mean? Numbers are funny. I never doubt such reports fromrespectable firms or people. But I am always skeptical about thenumbers themselves. Sure, those were the results obtained. Iwill accept this without hesitation. But they often do not seemin accord with my experience.I get lots and lots of spam. Less than 3% is po-rn related. Do I thus conclude the report was wrong? That they were lyingfor some devious purpose?Not at all. It only means their sample of email received was not representative of what I receive. In like fashion, it is doubtful my email is typical of yours. 100,000 spams messages is a very small percentage of what ismailed each day. It is so small, results from this sample havevery little, if any significance. These results were obtained,that's true. But they may have no meaning relative to you.Leave the particulars of demographics to those keen on thetopic. Your best plan is to ignore such numbers and focus oninteractivity with readers and visitors. In every way you can,seek input, then derive your own demographics from it.Your Log Files Can MisleadRecently I was chatting with a fellow who was having troublegetting a page to load under a specific condition in Netscape. Since he uses Internet Explorer, which handled this casecorrectly, he hadn't noticed the problem until I pointed it out.When I did, he commented, "Hey, I don't need to worry. Only5% of my visitors are using Netscape." This fellow is wrong in two ways.Of visitors to my site, over 40% are using Netscape. So haveI got it wrong? Or is the fellow reporting 5% wrong? Neither ofus is. We are both reporting accurately. Why Are There Such Great Differences?The apparent dilemma stems from the fact that we all have ourown set of visitors. Each comes to us from a vast pool of manymillions of Web users. Those who show up on my site may nevereven hear about yours, let alone visit. Thus my visitors are not representative of yours, except asto the fundamentals. For example, all site visitors ask first,"What's in it for me?" Such basics relate to every site. Thespecifics do not.Even if a massive, well respected study reported only 1% ofsurfers use 640 x 480 monitors, it still might not apply to yoursite. For as suggested above, the pool is so vast, hoping todraw a truly random sample from it is impossible.Further, things change rapidly on the Web. Not long ago,Netscape was the browser leader. As Microsoft continued todemand Internet Explorer be installed on all new systemsdelivered, the dominance of Netscape began to fade. Even afterbeing acquired by AOL, market share continued to drop.Can you assume it will continue to do so? That would leaveus with only one major browser. A Microsoft product. A companyalready at odds with the Justice department in anti-trustactions. It may prove to be in their best interest to assurethat Netscape regains a significant share of the market.What seems so today is suspect, for it may not be sotomorrow. Rather than making assumptions which may prove falsetomorrow, the better plan is to accommodate all possible optionstoday, and be prepared to make changes tomorrow.The Mistake That Matters MostBut the second mistake made by the fellow mentioned above is in ignoring Netscape users however small their numbers be. Suppose only 5% of my visitors use Netscape. To toss away thismany potential customers is foolish at least. I take the time to make it work for them.Hasten SlowlyJavaScript has been available for some time. Is it wise touse it if N% of systems can not deal with it? The better plan is to offer an alternate way to access your site for those who can not.Plug ins are popular of late. Will users take the time todownload and install one so as to see your site in all its glory? I doubt it. What's best is to offer the option to do so, but besure your site functions effectively without it.One of my systems uses a Pentium II with awesome supportingresources. However, it doesn't have a sound card. A site thatrequires I have one, will hold my attention only so long as ittakes to hit the Back button or enter another URL.Killer AssumptionsIf we make assumptions about the power and tools our visitorshave readily available, to the extent we are wrong, we aredriving them off our sites.When you consider how hard it is to draw a new visitor,driving even one away seems a pretty silly thing to do.
SPIDERS AND YOUR WEBSITE
An effective website must have a clearly defined purpose. And it must lead visitors to the action you want them to take. Nothing can be allowed to interfere in this. The chance of asearch engine spider liking such a site is slim to none. Your presentation may be pointed at making a sale, generating a lead, obtaining information, etc. But at is a sales pitch. This is not what spiders are looking for; they want content. While it is unwise to ignore search engines, all must be focused on the site purpose.To turn this around, suppose all your pages make every spider happy. And suppose all are in the top ten on most searchengines. Then you would expect a ton of hits. But not a one ofthem would do you any good if the site fails to do its job.Once the site is functioning as required, then the gamechanges. You can now think about adding great content pages that do rank well. (For ideas about building content pages, send any email to mailto:contentpage@sitetipsandtricks.com) And you can consider professional services that generate more hits. (For a dandy, see "Search Engine Positioning Done Right!"at
SPIDERS AND YOUR WEBSITE
An effective website must have a clearly defined purpose. And it must lead visitors to the action you want them to take. Nothing can be allowed to interfere in this. The chance of asearch engine spider liking such a site is slim to none. Your presentation may be pointed at making a sale, generating a lead, obtaining information, etc. But at is a sales pitch. This is not what spiders are looking for; they want content. While it is unwise to ignore search engines, all must be focused on the site purpose.To turn this around, suppose all your pages make every spider happy. And suppose all are in the top ten on most searchengines. Then you would expect a ton of hits. But not a one ofthem would do you any good if the site fails to do its job.Once the site is functioning as required, then the gamechanges. You can now think about adding great content pages that do rank well. (For ideas about building content pages, send any email to mailto:contentpage@sitetipsandtricks.com) And you can consider professional services that generate more hits. (For a dandy, see "Search Engine Positioning Done Right!"at
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars, an interstellar medium of gas and dust, and an unknown dark matter. Typical galaxies contain ten million[1] to one trillion[2] (107 to 1012) stars, all orbiting a common center of gravity. Galaxies can also contain a large number of multiple star systems and star clusters as well as various types of interstellar clouds.
Historically, galaxies have been categorized according to their visual morphology. The most common form is the elliptical galaxy, which, as the name suggests, has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with curving dusty arms. Peculiar galaxies are unusual forms that can result from the gravitational pull from other, nearby galaxies. These interactions (as well as merging galaxies) can induce episodes of significantly increased star building, producing what is called a starburst galaxy. Galaxies lacking a coherent structure are termed irregular galaxies.[3]
There are probably more than a hundred billion (1011) galaxies in the observable universe.[4] Most galaxies are a thousand to a hundred thousand[2] parsecs in diameter and are usually separated from one another by distances on the order of millions of parsecs (or megaparsecs).[5] Intergalactic space, the space between galaxies, is filled with a tenuous gas with an average density less than one atom per cubic metre. The majority of galaxies are organized into a heirarchy of associations called clusters, which, in turn, can form larger groups called super-clusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.[6]
Although theoretical, dark matter appears to account for around 90% of the mass of most galaxies. But the nature of these unseen components is not well understood. There is also some evidence that supermassive black holes may exist at the center of many, if not all, galaxies. These massive objects are believed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor just such an object within the core region.[7]
Contents
1 Etymology
2 Observation history
3 Types and morphology
3.1 Ellipticals
3.2 Spirals
3.3 Other morphologies
3.4 Dwarf
4 Unusual dynamics and activities
4.1 Interacting
4.2 Starburst
4.3 Active nucleus
5 Formation and evolution
5.1 Formation
5.2 Evolution
6 Larger scale structures
7 Multi-wavelength observation
8 See also
9 Notes
10 References
11 External links
//
[edit]
Etymology
The word galaxy derives from the Greek term for our own galaxy, galaxias (γαλαξίας) or kyklos galaktikos meaning "milky circle" for the system's appearance in the sky. In Greek mythology, Zeus placed his son by a mortal woman, the infant Hercules, on Hera's breast as she was asleep, so that the baby would drink her divine milk and thus become immortal. Hera woke up while breastfeeding, and realized that she was nursing an unknown baby: she pushed the baby away and a jet of her milk sprayed the night sky, producing the faint band of light known as the Milky Way.[8]
The terms galaxy and Milky Way first appeared in the English language in a poem by Chaucer.
“"See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt."”
—[[Geoffrey ChaucerGeoffrey Chaucer The House of Fame, c. 1380.[9]]]
When William Herschel constructed his catalog of deep sky objects, he used the name "spiral nebula" for certain objects such as M31. These would later be recognized as immense conglomerations of stars, once the true distance to these objects was appreciated, and they would be termed "Island universes". However the word universe was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.[10]
[edit]
Observation history
In 1610, Galileo Galilei used a telescope to study the bright band on the night sky known as the Milky Way and discovered that it was composed of a huge number of faint stars.[11] In a treatise in 1755, Immanuel Kant, drawing on earlier work by Thomas Wright, speculated (correctly) that the Galaxy might be a rotating body of a huge number of stars, held together by gravitational forces akin to the solar system but on much larger scales. The resulting disk of stars would be seen as a band on the sky from our perspective inside the disk. Kant also conjectured that some of the nebulae visible in the night sky might be separate galaxies.[12]
Sketch of the Whirlpool Galaxy by Lord Rosse in 1845
Towards the end of the 18th century, Charles Messier compiled a catalog containing the 109 brightest nebulae (celestial objects with a nebulous appearance), later followed by a larger catalog of five thousand nebulae assembled by William Herschel.[12] In 1845, Lord Rosse constructed a new telescope and was able to distinguish between elliptical and spiral-shaped nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.[13]
In 1917, Heber Curtis had observed the nova S Andromedae within the Messier object M31. Searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within our galaxy. As a result he was able to come up with a distance estimate of 150,000 parsecs. He became a proponent of the so-called "island universes" hypothesis that held the spiral nebulae were actually independent galaxies.[14]
In 1920 the so-called Great Debate took place between Harlow Shapley and Heber Curtis, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that M31 was an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in our own galaxies, as well as the significant Doppler shift.[15]
Edwin Hubble at the 48-inch telescope on Palomar Mountain.
The matter was conclusively settled by Edwin Hubble in the early 1920s using a new telescope. He was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.[16] In 1936, Hubble produced a classification system for galaxies that is used to this day, the Hubble sequence.[17]
The first attempt to describe the shape of the Milky Way and the position of the Sun within it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the sky. Using a refined approach, Kapteyn in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by Harlow Shapley based on the cataloging of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center.[12] Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane; once Robert Julius Trumpler had quantified this effect in 1930 by studying open clusters, the present picture of our galaxy as described above emerged.[18]
In 1944, Hendrik van de Hulst predicted microwave radiation at a wavelength of 21 cm, resulting from interstellar atomic hydrogen gas;[19] this radiation was observed in 1951. This radiation allowed for much improved study of the Galaxy, since it is not affected by dust absorption and its Doppler shift can be used to map the motion of the gas in the Galaxy. These observations led to the postulation of a rotating bar structure in the center of the Galaxy.[20] With improved radio telescopes, hydrogen gas could also be traced in other galaxies. In the 1970s it was discovered in Vera Rubin's study of the rotation speed of gas in galaxies that the total visible mass (from stars and gas) does not properly account for the speed of the rotating gas. This galaxy rotation problem is thought to be explained by the presence of large quantities of unseen dark matter.[21]
Beginning in the 1990s, the Hubble Space Telescope yielded improved observations. Among other things, it established that the missing dark matter in our galaxy cannot solely consist of inherently faint and small stars.[22] The Hubble Deep Field, an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about one hundred and seventy-five billion galaxies in the universe.[23] Improved technology in detecting the spectra invisible to humans (radio telescopes, infra-red cameras, x-ray telescopes), allow detection of other galaxies that are not detected by Hubble. Particularly, galaxy surveys in the zone of avoidance (the region of the sky blocked by the Milky Way) have revealed a number of new galaxies.[24]
[edit]
Types and morphology
Types of galaxies according to the Hubble classification scheme. An E indicates a type of elliptical galaxy; an S is a spiral, and SB is a barred-spiral galaxy
Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the Hubble sequence. Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as star formation rate (in starburst galaxies) or activity in the core (in active galaxies).[3]
[edit]
Ellipticals
The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little interstellar matter. Consequently these galaxies also have a low portion of open clusters and a reduced rate of new star formation. Instead the galaxy is dominated by generally older, more evolved stars that are orbiting the common center of gravity in random directions. In this sense they have some similarity to the much smaller globular clusters.[25]
The majority of galaxies are elliptical. Many elliptical galaxies are believed to form due to the interaction of galaxies, resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example) and giant elliptical galaxies are often found near the core of large galaxy clusters.[26] Starburst galaxies are the result of such a galactic collision that can result in the formation of an elliptical galaxy.[25]
[edit]
Spirals
Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the bulge are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type S, followed by a letter (a, b, or c) that indicates the degree of tightness of the spiral arms and the size of the central bulge. An Sa galaxy has tightly wound, poorly-defined arms and possesses a relatively large core region. At the other extreme, an Sc galaxy has open, well-defined arms and a small core region.[27]
In spiral galaxies, the spiral arms have the shape of approximate logarithmic spirals, a pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms also rotate around the center, but they do so with constant angular velocity. That means that stars pass in and out of spiral arms. The spiral arms are thought to be areas of high density or density waves. As stars move into an arm, they slow down, thus creating a higher density; this is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation and they therefore harbor many bright and young stars.
The barred spiral galaxy NGC 1300 (NASA/ESA Hubble Space Telescope photo)
A majority of spiral galaxies have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure.[28] In the Hubble classification scheme, these are designated by an SB, followed by a lower-case letter (a, b or c) that indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies.) Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from the core, or else due to a tidal interaction with another galaxy.[29] Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms.[30]
Our own galaxy, the Milky Way, sometimes simply called the Galaxy (with uppercase), is a large disk-shaped barred-spiral galaxy[31] about 30 kiloparsecs in diameter and a kiloparsec in thickness. It contains about two hundred billion (2×1011)[32] stars and has a total mass of about six hundred billion (6×1011) times the mass of the Sun.[33]
[edit]
Other morphologies
Peculiar galaxies are galactic formations that develop unusual properties due to tidal interactions with other galaxies. An example of this is the ring galaxy, which possesses a ring-like structure of stars and interstellar medium surrounding a bare core. A ring galaxy is thought to occur when a smaller galaxy passes through the core of a spiral galaxy.[34] Such an event may have affected the Andromeda galaxy, and as a result it displays a multi-ring-like structure when viewed in infrared radiation.[35]
A lenticular galaxy is an intermediate form that has properties of both elliptical and spiral galaxies. These are categorized as Hubble type S0, and they possess ill-defined spiral arms with an elliptical halo of stars.[36] (Barred lenticular galaxies receive Hubble classification SB0.)
In addition to the classifications mentioned above, there are a number of galaxies that can not be readily classified into an elliptical or spiral morphology. These are categorized as irregular galaxies. An Irr-I galaxy has some structure but does not align cleanly with the Hubble classification scheme. Irr-II galaxies does not possess any structure that resembles a Hubble classification, and may have been disrupted.[37] Nearby examples of (dwarf) irregular galaxies include the Magellanic clouds.
[edit]
Dwarf
Despite the prominence of large elliptical and spiral galaxies, most galaxies in the universe appear to be dwarf galaxies. These tiny galaxies are about one hundred times smaller than the Milky Way, containing only a few billion stars. Ultra-compact dwarf galaxies have recently been discovered that are only 100 parsecs across.[38]
Many dwarf galaxies may orbit a single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 3–500 yet to be discovered.[39] Dwarf galaxies may also be classified as elliptical, spiral or irregular. Since small dwarf ellipticals bear little resemblance to large ellipticals, they are often called dwarf spheroidal galaxies instead.
[edit]
Unusual dynamics and activities
[edit]
Interacting
The average separation between galaxies within a cluster is a little over an order of magnitude larger than their diameter. Hence interactions between these galaxies are relatively frequent, and play an important role in their evolution. Near misses between galaxies result in warping distortions due to tidal interactions, and may cause some exchange of gas and dust.[40][41]
Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge. The stars within these interacting galaxies will typically pass straight through without colliding. However the gas and dust within the two forms will interact. This can trigger bursts of star formation as the interstellar medium becomes disrupted and compressed. A collision can severely distort the shape of one or both galaxies, forming bars, rings or tail-like structures.[40][41]
At the extreme of interactions are galactic mergers. In this case the relative momentum of the two galaxies is insufficient to allow the galaxies to pass through each other. Instead they gradually merge together to form a single, larger galaxy. Mergers can result in significant changes to morphology, as compared to the original galaxies. In the case where one of the galaxies is much more massive, however, the result is known as cannibalism. In this case the larger galaxy will remain relatively undisturbed by the merger, while the smaller galaxy is torn apart. The Milky Way galaxy is currently in the process of cannibalizing the Sagittarius Dwarf Elliptical Galaxy and the Canis Major Dwarf Galaxy.[40][41]
[edit]
Starburst
M82, the archetype starburst galaxy, has experienced a 10-fold increase[42] in star formation rate as compared to a "normal" galaxy (NASA/ESA/STSci image)
Stars are created within galaxies from a reserve of cold gas that forms into giant molecular clouds. Some galaxies have been observed to form stars at an exceptional rate, known as a starburst. Should they continue to do so, however, they would consume their reserve of gas in a time frame lower than the lifespan of the galaxy. Hence starburst activity usually lasts for only about ten million years; a relatively brief period in the history of a galaxy. Starburst galaxies were more common during the early history of the universe,[43] and, at present, still contribute an estimated 15% to the total star production rate.[44]
Starburst galaxies are characterized by dusty concentrations of gas and the appearance of newly-formed stars, including massive stars that ionize the surrounding clouds to create H II regions.[45] These massive stars also produce supernova explosions, resulting in expanding remnants that interact powerfully with the surrounding gas. These outbursts trigger a chain reaction of star building that spreads throughout the gaseous region. Only when the available gas is nearly consumed or dispersed does the starburst activity come to an end.[43]
Starbursts are often associated with merging or interacting galaxies. The prototype example of such a starburst-forming interaction is M82, which experienced a close encounter with the larger M81. Irregular galaxies often exhibit spaced knots of starburst activity.[46]
[edit]
Active nucleus
A portion of the galaxies we can observe are classified as active. That is, a significant portion of the total energy output from the galaxy is emitted by a source other than the stars, dust and interstellar medium.
The standard model for an active galactic nucleus is based upon an accretion disk that forms around supermassive black hole (SMBH) at the core region. The radiation from an active galactic nucleus results from the gravitational energy of matter as it falls toward the black hole from the disk.[47] In about 10% of these objects, a diametrically opposed pair of energetic jets ejects particles from the core at velocities close to the speed of light. The mechanism for producing these jets is still not well-understood.[48]
A jet of particles is being emitted from the core of the elliptical radio galaxy M87 (NASA/ESA Hubble Space Telescope image)
Active galaxies that emit high-energy radiation in the form of x-rays are classified as Seyfert galaxies or quasars, depending on the luminosity. Blazars are believed to be an active galaxy with a relativistic jet that is pointed in the direction of the Earth. A radio galaxy emits radio frequencies from relativistic jets. A unified model of these types of active galaxies explains their differences based on the viewing angle of the observer.[48]
Possibly related to active galactic nuclei (as well as starburst regions) are low-ionization nuclear-emission regions, or LINERs. The emission from LINER-type galaxies is dominated by weakly-ionized elements.[49] Approximately one-third of nearby galaxies are classified as containing LINER nuclei.[47][49][50]
[edit]
Formation and evolution
The study of galactic formation and evolution attempts to answer questions regarding how galaxies formed and their evolutionary path over the history of the universe. Some theories on this field have now become widely accepted, but it is still an active area of study in astrophysics.
[edit]
Formation
The method of galactic formation is a major open question in astronomy. Theories may be divided into two categories: top-down and bottom-up. In top-down theories such as the Eggen–Lynden-Bell–Sandage (ELS) model, protogalaxies form in a large-scale simultaneous collapse lasting about one hundred million years.[51] In bottom-up theories such as the Searle-Zinn (SZ) model, globular clusters form first, and then a number of such bodies accrete to form a larger galaxy.[52] Modern theories must be modified to account for the probable presence of large dark matter halos.
Shortly after recombination, baryonic matter begins to condense around cold dark matter halos. Zero-metal, possibly massive halo stars (called Population III stars) are the first to develop around a protogalaxy as it starts to contract. These huge stars quickly supernova, releasing heavy elements into the interstellar medium.[53]
During this early era of the universe, most of the hydrogen was neutral (non-ionized), which readily absorbs light. (As a result this period has been called the "Dark Ages".) However the first generation of stars re-ionized the surrounding neutral hydrogen, creating ever-expanding bubbles of transparent space through which light could readily travel.[54]
In 2006 it was discovered that the emission of Lyman alpha radiation from galaxy IOK-1 has a redshift of 6.96, making it thirteen billion years old. While some scientists have claimed other objects (such as Abell 1835 IR1916) to be even older, the IOK-1's age and composition have been more reliably established.[55] The existence of such early protogalaxies suggests that they must have grown in the so-called "Dark Ages", from anisotropic irregularities present during the era of recombination, a few hundred thousand years after the Big Bang.[56] Such irregularities of the right scale were observed using the Wilkinson Microwave Anisotropy Probe (WMAP) in 2003.[57]
[edit]
Evolution
Within a billion years of a galaxy's formation, globular clusters, the central supermassive black hole and galactic bulge of metal-poor Population II stars form. The supermassive black hole appears to play a key role in actively regulating the growth of galaxies by limiting the total amount of accumulated matter.[58]
I Zwicky 18 (lower left) is a recently-formed galaxy that may still be producing its first generation of stars.[59] NASA/ESA Hubble Space Telescope image.
During the following two billion years, the remaining material settles into a galactic disk.[60] Galaxies will continue to absorb infalling material from high velocity clouds and dwarf galaxies throughout its life;[61] the cycle of stellar birth and death will increase the abundance of heavy elements, eventually allowing the formation of planets.[62]
The evolution of galaxies can be significantly affected by interactions and collisions. Mergers of galaxies were common during the early epoch, and the majority of galaxies were peculiar in morphology.[63] Given the distances between the stars, the great majority of stellar systems in colliding galaxies will be unaffected. However, gravitational stripping of the interstellar gas and dust that makes up the spiral arms will produce a long train of stars, similar to that seen in NGC 250[64] or the Antennae Galaxies.[65]
Studies show that the Milky Way galaxy is moving towards the nearby Andromeda Galaxy at about 130 km/s, and depending upon the lateral movements, the two may collide in about five to six billion years. Although the Milky Way has never collided with a galaxy as large as Andromeda before, evidence of past collisions of the Milky Way with smaller dwarf galaxies is increasing.[66]
As time passed, the merging of large galaxies steadily declined until it had virtually ceased after about six billion years. Most bright galaxies have retained their form since that time, and only a small percentage are now peculiar. The net formation of stars also peaked at about two billion years after the big bang and has steadily decreased since then. In fact the majority of star formation now occurs in smaller galaxies where the cool gas has not been as depleted.[63]
Spiral galaxies, like the Milky Way, only produce new generations of stars as long as they continue to have dense molecular clouds of interstellar hydrogen in their spiral arms.[67] Elliptical galaxies are already largely devoid of this gas and so form no new stars.[68] However, the supply of star-forming material is finite; once stars have converted the available supply of hydrogen into heavier elements, new star will come to an end.[69]
After the end of stellar formation in under one hundred billion years, the "stellar age" will come to an end after about ten trillion to one hundred trillion years (1013–1014 years), as the smallest longest-lived stars in our astrosphere, tiny red dwarfs begin to fade. At the end of the stellar age galaxies will comprise compact objects: brown dwarfs, black dwarfs, cooling white dwarfs, neutron stars, and black holes. Eventually, as a result of gravitational relaxation, all stars will either fall into the central supermassive black hole of the galaxies, or be flung into the depths of intergalactic space as a result of collisions.[70][69]
[edit]
Larger scale structures
Deep sky surveys of galaxies have demonstrated that they are often found in relatively close association with other galaxies. Solitary galaxies, which may be defined as galaxies that have not significantly interacted with another galaxy of comparable mass during the past billion years (1 Gyr), are relatively scarce. Only about 5% of the galaxies surveyed have been found to be truly isolated. However, these isolated formations may have interacted and even merged with other galaxies in the past, and can still be orbited by smaller, satellite galaxies. Isolated galaxies[a] can produce stars at a higher rate than normal, as their gas is not being stripped by other, nearby galaxies.[71]
On the largest scale the universe is continually expanding, resulting in an average increase in the separation between individual galaxies. (See Hubble's law.) However, associations of galaxies can overcome this expansion on a local scale through their mutual gravitational attraction. These associations formed early in the universe as clumps of dark matter pulled their respective galaxies together. Nearby groups later merged to form larger-scale clusters. This on-going merger process (as well as an influx of infalling gas) heats the inter-galactic gas within a cluster to very high temperatures, reaching 30–100 million K.[72] About 70–80% of the mass in a cluster is in the form of dark matter, with 10–30% consisting of this heated gas and the remaining few percent of the matter in the form of galaxies.[73]
Seyfert's Sextet is an example of a compact galaxy group. NASA Hubble Space Telescope image.
Most galaxies in the universe are gravitationally bound to a number of other galaxies. These form a fractal-like heirarchy of clustered structures, with the smallest such associations being termed groups. A group of galaxies is the most common type of galactic cluster, and these formations contain a majority of the galaxies (as well as most of the baryonic mass) in the universe.[74][75] To remain gravitationally bound to such a group, each member galaxy must have a sufficiently low velocity to prevent it from escaping. (See Virial theorem.) If there is insufficient kinetic energy, however, the group may evolve into a smaller number of galaxies through mergers.[76]
Larger structures containing many thousands of galaxies packed into an area a few megaparsecs across are called clusters. Clusters of galaxies are often dominated by a single giant elliptical galaxy, known as the brightest cluster galaxy, which, over time, tidally destroys its satellite galaxies and adds their mass to its own.[77]
Superclusters are giant collections containing tens of thousands of galaxies, found in clusters, groups and sometimes individually; at the supercluster scale, galaxies are arranged into sheets and filaments surrounding vast empty voids.[78] Above this scale, the universe appears to be isotropic and homogeneous.[79]
Our galaxy is a member of an association named the Local Group, a relatively small group of galaxies that has a diameter of approximately one megaparsec. The Milky Way and the Andromeda Galaxy are the two brightest galaxies within the group. Many of the other member galaxies are dwarf companions of these two galaxies.[80] The Local Group itself is a part of a cloud-like structure within the Virgo Supercluster, a large, extended structure of groups and clusters of galaxies centered around the Virgo Cluster.[81]
[edit]
Multi-wavelength observation
Since galaxies external to the Milky Way were found to exist, much of the initial observation of these objects was been performed in the visual portion of the electromagnetic spectrum. The peak radiation of most stars lies in this band, so the observation of the stars that form galaxies has been a major component of optical astronomy. It is also a favorable portion of the spectrum for observing ionized HII regions, and for examining the distribution of dusty arms.
Unfortunately the dust present in the interstellar medium is opaque to visual light, so it is necessary to use the infrared part of the spectrum to observe these regions. The dust is more transparent to far-infrared, allowing the interior regions of giant molecular clouds and galactic cores to be observed in great detail.[82] Infrared is also beneficial for the observation of distant, red-shifted galaxies that were formed much earier in the universe. Unfortunately water vapor and carbon dioxide absorb a number of useful portions of the infrared spectrum, requiring high-altitude or space-based telescope to perform infrared astronomy.
A radio map of the galaxy Centaurus A (upper left and lower right) is overlaid across the optical image (center), showing two lobes from the jets being generated by an active nucleus. (NASA image.)
The first non-visual study of galaxies, particularly active galaxies, was made using radio frequencies. The atmosphere is nearly transparent to radio between 5 MHz and 30 GHz. (The ionosphere blocks signals below this range.)[83] Large radio interferometers have been used to map the active jets emitted from active nuclei. Radio telescopes can also be used to observe neutral hydrogen (via 21 centimeter radiation), including, potentially, the non-ionized matter in the early universe that would later collapse to form galaxies.[84]
Ultraviolet and X-ray telescopes can observe highly energetic galactic phenomenon. An ultraviolet flare has been observed as a star in a distant galaxy was torn apart from the tidal forces of a black hole.[85] X-rays emitted by hot gas in galactic clusters allows the distribution of this material to be mapped. The existence of super-massive black holes at the cores of galaxies was confirmed through X-ray astronomy.[86]
See also: Observational astronomy
[edit]
See also
List of galaxies
List of nearest galaxies
Timeline of galaxies, clusters of galaxies, and large scale structure
[edit]
Notes
^ The term "field galaxy" is sometimes used to mean an isolated galaxy, although the same term is also used to describe galaxies that do not belong to a cluster but may be a member of a group of galaxies.
[edit]
References
↑ Unveiling the Secret of a Virgo Dwarf Galaxy. ESO (May 3, 2000). Retrieved on 2007-01-03.
↑ 2.0 2.1 Hubble's Largest Galaxy Portrait Offers a New High-Definition View. NASA (February 28, 2006). Retrieved on 2007-01-03.
↑ 3.0 3.1 Jarrett, T.H.. Near-Infrared Galaxy Morphology Atlas. California Institute of Technology. Retrieved on 2007-01-09.
↑ Mackie, Glen (February 1, 2002). To see the Universe in a Grain of Taranaki Sand. Swinburne University. Retrieved on 2006-12-20.
↑ D. Gilman. The Galaxies: Islands of Stars. NASA WMAP. Retrieved on 2006-08-10.
↑ Galaxy Clusters and Large-Scale Structure. University of Cambridge. Retrieved on 2007-01-15.
↑ D. Finley, D. Aguilar (November 2, 2005). Astronomers Get Closest Look Yet At Milky Way's Mysterious Core. National Radio Astronomy Observatory. Retrieved on 2006-08-10.
↑ Koneãn˘, Lubomír. Emblematics, Agriculture, and Mythography in The Origin of the Milky Way (PDF). Academy of Sciences of the Czech Republic. Retrieved on 2007-01-05.
↑ Online Etymology Dictionary. Retrieved on 2007-01-03.
↑ Rao, Joe (September 2, 2005). Explore the Archer's Realm. space.com. Retrieved on 2007-01-03.
↑ J. J. O'Connor, E. F. Robertson (November, 2002). Galileo Galilei. University of St Andrews. Retrieved on 2007-01-08.
↑ 12.0 12.1 12.2 Evans, J. C. (November 24, 1998). Our Galaxy. George Mason University. Retrieved on 2007-01-04.
↑ Abbey, Lenny. The Earl of Rosse and the Leviathan of Parsontown. The Compleat Amateur Astronomer. Retrieved on 2007-01-04.
↑ Heber D. Curtis (January 1988). "Novae in Spiral Nebulae and the Island Universe Theory". Publications of the Astronomical Society of the Pacific 100: 6.
↑ Weaver, Harold F.. Robert Julius Trumpler. National Academy of Sciences. Retrieved on 2007-01-05.
↑ E. P. Hubble (1929). "A spiral nebula as a stellar system, Messier 31". Astrophysical JournalEngl 69: 103-158.
↑ Sandage, Allan (1989). "Edwin Hubble, 1889-1953". The Journal of the Royal Astronomical Society of Canada 83 (6). Retrieved on 2007-01-08.
↑ Trimble, V. (1999). "Robert Trumpler and the (Non)transparency of Space". Bulletin of the American Astronomical Society (31): 1479. Retrieved on 2007-01-08.
↑ Tenn, Joe. Hendrik Christoffel van de Hulst. Sonoma State University. Retrieved on 2007-01-05.
↑ M. López-Corredoira, P. L. Hammersley, F. Garzón, A. Cabrera-Lavers, N. Castro-Rodríguez, M. Schultheis, T. J. Mahoney (2001). "Searching for the in-plane Galactic bar and ring in DENIS". Astronomy and Astrophysics 373: 139-152. Retrieved on 2007-01-08.
↑ 2002 Cosmology Prize Recipient—Vera Rubin, Ph.D.. Peter Gruber Foundation. Retrieved on 2007-01-05.
↑ "Hubble Rules Out a Leading Explanation for Dark Matter", Hubble News Desk, October 17, 1994. Retrieved on 2007-01-08.
↑ How many galaxies are there?. NASA (November 27, 2002). Retrieved on 2007-01-08.
↑ R. C. Kraan-Korteweg, S. Juraszek (2000). "Mapping the hidden universe: The galaxy distribution in the Zone of Avoidance". Publications Astronomical Society of Australia 17 (1): 6-12.
↑ 25.0 25.1 Elliptical Galaxies. Leicester University Physics Department (2005). Retrieved on 2006-06-08.
↑ Galaxies. Cornell University (October 20 2005). Retrieved on 2006-08-10.
↑ Smith, Gene (March 6, 2000). Galaxies - The Spiral Nebulae. University of California, San Diego Center for Astrophysics & Space Sciences. Retrieved on 2006-11-30.
↑ P. B. Eskridge, J. A. Frogel (1999). "What is the True Fraction of Barred Spiral Galaxies?". Astrophysics and Space Science 269/270: 427-430.
↑ F. Bournaud, F. Combes (2002). "Gas accretion on spiral galaxies: Bar formation and renewal". Astronomy and Astrophysics 392: 83-102.
↑ J. H. Knapen, D. Pérez-Ramírez, S. Laine (2002). "Circumnuclear regions in barred spiral galaxies - II. Relations to host galaxies". Monthly Notice of the Royal Astronomical Society 337 (3): 808-828.
↑ C. Alard (2001). "Another bar in the Bulge". Astronomy and Astrophysics 379 (2): L44-L47.
↑ Sanders, Robert. "Milky Way galaxy is warped and vibrating like a drum", UCBerkeley News, January 9, 2006. Retrieved on 2006-05-24.
↑ G. R. Bell, S. E. Levine (1997). "Mass of the Milky Way and Dwarf Spheroidal Stream Membership". Bulletin of the American Astronomical Society 29 (2): 1384.
↑ R. A. Gerber, S. A. Lamb, D. S. Balsara (1994). "Ring Galaxy Evolution as a Function of "Intruder" Mass". Bulletin of the American Astronomical Society 26: 911.
↑ Esa Science News (October 14, 1998). ISO unveils the hidden rings of Andromeda. Press release. Retrieved on 2006-05-24.
↑ Spitzer Reveals What Edwin Hubble Missed. Harvard-Smithsonian Center for Astrophysics (May 31, 2004). Retrieved on 2006-12-06.
↑ Barstow, M.A. (2005). Irregular Galaxies. University of Leicester. Retrieved on 2006-12-05.
↑ S. Phillipps, M. J. Drinkwater, M. D. Gregg, J. B. Jones (2001). "Ultracompact Dwarf Galaxies in the Fornax Cluster". The Astrophysical Journal 560 (1): 201–206.
↑ Groshong, Kimm. "Strange satellite galaxies revealed around Milky Way", NewScientist, April 24, 2006. Retrieved on 2007-01-10.
↑ 40.0 40.1 40.2 Galaxy Interactions. University of Maryland Department of Astronomy. Retrieved on 2006-12-19.
↑ 41.0 41.1 41.2 Interacting Galaxies. Swinburne University. Retrieved on 2006-12-19.
↑ Happy Sweet Sixteen, Hubble Telescope!. NASA (April 24, 2006). Retrieved on 2006-08-10.
↑ 43.0 43.1 Starburst Galaxies. Harvard-Smithsonian Center for Astrophysics (August 29, 2006). Retrieved on 2006-08-10.
↑ R. C. Kennicutt Jr., J.C. Lee, J.G. Funes, S. Shoko, S. Akiyama (6-10 September 2004). "Demographics and Host Galaxies of Starbursts". Starbursts: From 30 Doradus to Lyman Break Galaxies, 187-, Cambridge, UK: Dordrecht: Springer. Retrieved on 2006-12-11.
↑ Smith, Gene (2006-07-13). Starbursts & Colliding Galaxies. University of California, San Diego Center for Astrophysics & Space Sciences. Retrieved on 2006-08-10.
↑ Keel, Bill (September, 2006). Starburst Galaxies. University of Alabama. Retrieved on 2006-12-11.
↑ 47.0 47.1 Keel, William C. (2000). Introducing Active Galactic Nuclei. The University of Alabama. Retrieved on 2006-12-06.
↑ 48.0 48.1 J. Lochner, M. Gibb. A Monster in the Middle. NASA. Retrieved on 2006-12-20.
↑ 49.0 49.1 T. M. Heckman (1980). "An optical and radio survey of the nuclei of bright galaxies - Activity in normal galactic nuclei". Astronomy and Astrophysics 87: 152-164.
↑ L. C. Ho, A. V. Filippenko, W. L. W. Sargent (1997). "A Search for "Dwarf" Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby Galaxies". Astrophysical Journal 487: 568-578.
↑ O. J. Eggen, D. Lynden-Bell, A. R. Sandage (1962). "Evidence from the motions of old stars that the Galaxy collapsed". Reports on Progress in Physics 136: 748.
↑ L. Searle, R. Zinn (1978). "Compositions of halo clusters and the formation of the galactic halo". Astrophysical Journal 225 (1): 357-379.
↑ A. Heger, S. E. Woosley (2002). "The Nucleosynthetic Signature of Population III". Astrophysical Journal 567 (1): 532-543.
↑ R. Barkana, A. Loeb (1999). "In the beginning: the first sources of light and the reionization of the universe". Physics Reports 349 (2): 125-238.
↑ McMahon, R. (2006). "Journey to the birth of the Universe". Nature 443.
↑ Search for Submillimeter Protogalaxies. Harvard-Smithsonian Center for Astrophysics (November 18, 1999). Retrieved on 2007-01-10.
↑ Seife, Charles (2003). "With Its Ingredients MAPped, Universe's Recipe Beckons". Science 300 (5620): 730-731.
↑ "Simulations Show How Growing Black Holes Regulate Galaxy Formation", Carnegie Mellon University, February 9, 2005. Retrieved on 2007-01-07.
↑ R. Villard, F. Samarrai, T. Thuan, G. Ostlin. "Hubble Uncovers a Baby Galaxy in a Grown-Up Universe", HubbleSite News Center, December 1, 2004. Retrieved on 2007-01-11.
↑ Noguchi, Masafumi (1999). "Early Evolution of Disk Galaxies: Formation of Bulges in Clumpy Young Galactic Disks". Astrophysical Journal 514 (1): 77-95. Retrieved on 2007-01-16.
↑ C. Baugh, C. Frenk (May 1999). How are galaxies made?. Physics Web. Retrieved on 2007-01-16.
↑ Gonzalez, G. (1998). "The Stellar Metallicity - Planet Connection". Proceedings of a workshop on brown dwarfs and extrasolar planets, 431. Retrieved on 2007-01-16.
↑ 63.0 63.1 Conselice, Christopher J. (February, 2007). "The Universe's Invisible Hand". Scientific American 296 (2): 35-41.
↑ A. W. McConnachie, M. J. Irwin, G. F. Lewis, R. A. Ibata, S. C. Chapman, A. M. N. Ferguson, N. R. Tanvir (2004). "The tidal trail of NGC 205?". Monthly Notices of the Royal Astronomical Society 351 (4): L94-L98.
↑ Struck, Curtis (1999). "Galaxy Collisions". Galaxy Collisions 321.
↑ Wong, Janet. "Astrophysicist maps out our own galaxy's end", University of Toronto, April 14, 2000. Retrieved on 2007-01-11.
↑ R. C. Kennicutt Jr., P. Tamblyn, C. E. Congdon (1994). "Past and future star formation in disk galaxies". Astrophysical Journal 435 (1): 22-36.
↑ G. R. Knapp (1999). Star Formation in Early Type Galaxies. ISBN 1-886733-84-8.
↑ 69.0 69.1 Fred Adams, Greg Laughlin (2006-07-13). The Great Cosmic Battle. Astronomical Society of the Pacific. Retrieved on 2007-01-16.
↑ Pobojewski, Sally (January 21, 1997). Physics offers glimpse into the dark side of the universe. University of Michigan. Retrieved on 2007-01-13.
↑ McKee, Maggie (June 7, 2005). Galactic loners produce more stars. New Scientist. Retrieved on 2007-01-15.
↑ Groups & Clusters of Galaxies. NASA Chandra. Retrieved on 2007-01-15.
↑ Ricker, Paul. When Galaxy Clusters Collide. National Partnership for Advanced Computational Infrastructure. Retrieved on 2007-01-15.
↑ Dahlem, Michael (November 24, 2006). Optical and radio survey of Southern Compact Groups of galaxies. University of Birmingham Astrophysics and Space Research Group. Retrieved on 2007-01-15.
↑ Ponman, Trevor (February 25, 2005). Galaxy Systems: Groups. University of Birmingham Astrophysics and Space Research Group. Retrieved on 2007-01-15.
↑ M. Girardi, G. Giuricin (2000). "The Observational Mass Function of Loose Galaxy Groups". The Astrophysical Journal 540 (1): 45–56.
↑ Dubinski, John (1998). "The Origin of the Brightest Cluster Galaxies". Astrophysical Journal 502 (2): 141-149.
↑ Bahcall, Neta A. (1988). "Large-scale structure in the universe indicated by galaxy clusters". Annual review of astronomy and astrophysics 26: 631-686.
↑ N. Mandolesi, P. Calzolari, S. Cortiglioni, F. Delpino, G. Sironi (1986). "Large-scale homogeneity of the Universe measured by the microwave background". Letters to Nature 319: 751-753.
↑ van den Bergh, Sidney (2000). "Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific 112 (770): 529-536.
↑ R. B. Tully (1982). "The Local Supercluster". Astrophysical Journal 257: 389-422.
↑ Near, Mid & Far Infrared. IPAC/NASA. Retrieved on 2007-01-02.
↑ The Effects of Earth's Upper Atmosphere on Radio Signals. NASA. Retrieved on 2006-08-10.
↑ "Giant Radio Telescope Imaging Could Make Dark Matter Visible", ScienceDaily, December 14, 2006. Retrieved on 2007-01-02.
↑ "NASA Telescope Sees Black Hole Munch on a Star", NASA, December 5, 2006. Retrieved on 2007-01-02.
↑ Dunn, Robert. An Introduction to X-ray Astronomy. Institute of Astronomy X-Ray Group. Retrieved on 2007-01-02.
General references:
Dickinson, Terence (2004). The Universe and Beyond, 4th, Firefly Books Ltd.. ISBN 1552979016.
James Binney, Michael Merrifield (1998). Galactic Astronomy. Princeton University Press. ISBN 0691004021.
