Astronomer: Beginner Tips

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abuali
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Astronomer: Beginner Tips

Postby abuali » 11 Sep 2009, 01:24

Advice for First Time Telescope Buyers
http://www.rocketroberts.com/astro/first.htm
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First...BEFORE you buy a telescope!

Many amateur astronomers will tell you that the best way to get into astronomy is to first learn some of the basic constellations, and then use a pair of binoculars to find your first "deep sky" objects. It is important to learn the basics of finding your way around the sky (you will need these skills to find objects using a telescope). Binoculars really can show quite a number of interesting sights in the night sky. A good pair of binoculars will often cost less than a telescope; in fact, if your budget only allows spending about $100, you might be better off buying a decent pair of binoculars and a good starter book rather than a telescope. Most experienced amateur astronomers agree that "jumping in" with a fancy telescope without first learning the basics is not the way to get involved. Astronomy is a fascinating hobby but it's not for everyone. If you "jump in" and spend $1000 on a fancy telescope and then later find you're not really into it, you will have wasted a considerable amount of money. Binoculars are a great way to get a taste of what backyard astronomy can offer. Another great way to start in astronomy is to visit a local astronomy club (most cities have some kind of club). Clubs often have loaner scopes, or at minimum, there will be members that will be happy to show you a number of telescopes. Binoculars can be a good first step, but they won't show any detail on the planets (and limited detail on the Moon). If you have a pair now, do try them out.

Ready for a telescope? Please read on!

Number One: Have realistic expectations!

DON'T EXPECT a small telescope to show images like those you may have seen in magazines. Those pictures are likely from the Hubble Space Telescope or some other large professional telescope. If you are expecting "video game" or "Hollywood" type images with amazing detail and vivid color, you will be in for a letdown.

What can you expect to see? Below we will describe what you might reasonably expect to see with small telescope:

  • The Moon: The Moon is a target that will show tremendous detail in an decent small scope. Even a telescope as small as 2.4 inches (60mm) will reveal a wealth of detail. You'll be able to see craters, mountains, "seas", and a number of other fine details. The Moon rarely dissapoints a first time viewer!
  • Mercury: Mercury is hard to see because it never gets far enough away from the Sun. If you do manage to locate it, at best you will only see the phase (no surface detail can be seen even with large telescopes).
  • Venus: Venus is also is also fairly close to the Sun and harder to see. When you do see it expect only to see its phase in a telescope; no surface detail will be seen since the planet's surface is permanently hidden by a thick, white atmosphere.
  • Mars: Mars is easily seen in a small telescope, but often a big disappointment to first time viewers. It only reveals subtle detail when it is close to Earth (and this occurs for a period of about 2 months every few years). When Mars is close to Earth, you might see a white polar cap, and perhaps some surface markings. The biggest problem with Mars is that it's a small planet. Even at high powers in a large telescope Mars at best looks about the same size as atennis ball viewed (with the naked eye) from about ten feet!
  • Jupiter: Jupiter is the planet that consistently shows the most detail in amateur telescopes. However, even at high magnification Jupiter will only look about the size of some of the medium sized craters on the Moon. On any given night you'd be able to see cloud bands, the 4 Galilean Moons, and maybe the Great Red Spot.
  • Saturn: Saturn will show its glorious rings, but the planet will not look too large even at magnification of around 100x. Keen eyed people (with good viewing conditions) might also spot some subtle cloud bands. Saturn's largest moon Titan will also be visible nearby but only as a moderately bright dot.
  • Uranus: You'll need to know exactly where to look to find Uranus. At best it will look like a small green dot. Even in large telescopes Uranus shows only as a small, featureless disk!
  • Neptune: Like Uranus, you'll need to know exactly where to look, and at best Neptune will look like a somewhat dim small blue dot (it won't really look any different than a star). No amateur scope can see any detail on Neptune.
  • Pluto: Pluto is out of the question for a small telescope; it generally requires an experienced observer using at least an 8 inch telescope (in a dark sky with a highly detailed finder chart) just to see it as a very faint dot!
  • The Sun: You can look at the Sun with a small telescope, however you MUST USE A SPECIAL FILTER FOR OBSERVING THE SUN WITH ANY TELESCOPE. Failure to do so will result in permanent blindness. DO NOT attempt solar observation unless you are sure you have the correct special equipment AND you know proper procedures. Solar observation is safe if you adhere to proper procedures! You can see sunspots and solar "granulation". If in doubt about observing the Sun, have an experienced amateur astronomer with you prior to solar observing... your eyesight is at stake!
  • Stars: Stars stars will look brighter in a telescope but they will not look any larger. No amateur telescope has anything close to the power required to make a star look larger! They are simply too far away...
  • Deep Sky Objects: In addition to planets and the Moon, there are a number of other objects within the reach of a small telescope. These are the so called "deep sky" objects. These include galaxies, star clusters, nebulae, and double stars. However, the quality of the view you will have on these kinds of objects depends to a very large degree on how much light pollution you have in your area (more on light pollution below). To locate most of these objects you'll have to use a star atlas (first you'll have to learn the basic constellations in order to find your way around the sky). Again, don't expect to see galaxies and nebulae like they appear in most magazine photos. Most galaxies and nebulae appear as "fuzzy patches of light" in small (and even large) telescopes. Star clusters and double stars are often quite beautiful and are good targets for small telescopes.
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Re: Astronomer: Beginner Tips

Postby Muhammad Mahdi » 11 Sep 2009, 03:08

Thanks for the interesting read.
I remember how nice the craters on the moon looked with my 300mm :D
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Re: Astronomer: Beginner Tips

Postby abuali » 11 Sep 2009, 03:17

Number Two: Don't blame the telescope for things it can't control!

Many beginners don't realize that a telescope's performance is often at the mercy of local ambient conditions. Other than the obvious (clouds, fog, etc.), there are several other major factors which limit how much can be seen.

  • First, it is important to give a telescope a chance to cool down to the outside temperature (especially for Newtonian Reflectors and Schmidt Cassegrain Telescopes). Cooling down of the scope is called thermal stabilization. If a telescope is brought from a warm house out to the cold night, the images seen through it are likely to be very bad at first, perhaps to the point where the telescope won't even seem to focus at all. This is because the optics in the telescope are undergoing a change in size due to the temperature difference. The actual change in the optics is extremely small in human terms; however, at the wavelengths of light, it is very significant. Bottom line: Make sure a telescope has time to cool down to the outside temperature before expecting it to perform at its best. Acceptable performance is usually reached with 15 to 20 minutes, but the very best performance may take one hour or more (depending on the temperature differential and the type of telescope). Storing a telescope in an unheated garage may help to shorten the time it takes to cool; alternatively, set the telescope outside an hour or so before you plan to use it. Keep in mind that even after it has cooled down the images still may not be too good. This is often due to the topic of the next paragraph, seeing conditions.

  • Second, seeing conditions are very important for good viewing (especially so for the planets and the Moon). When you look at an astronomical target, you are seeing it through the Earth's atmosphere, which essentially is an "ocean of air". Very often the atmosphere is highly unsteady, due to thermal variations in the upper atmosphere, air currents near the ground, etc. All of this means that an image passing though it will be distorted to some degree. Have you ever looked over a toaster while toasting some bread? The image of objects behind the toaster seems to shimmer. Now, imagine looking through miles of turbulent air at high magnification! In short, bad seeing conditions can severely limit the amount of fine detail you can see (fortunately bad seeing has much less effect on galaxies, star clusters and nebulae). Seeing conditions are often a function of where you live. Areas like Florida are known for good seeing (New England seeing is often notoriously poor). Also, never "look" over a house after sunset, a paved parking lot, etc. The heat that such items absorb during the day gets radiated at night and can fowl the seeing conditions.

  • The third major (and rapidly growing) problem facing astronomers is light pollution, a problem that is unknown to most non-astronomers. Light Pollution has (for all practical purposes) completely ruined the skies of just about any moderate to large city (this means that the only things you'll probably be able to see well are the Moon and bright planets). Light pollution is caused by excessive amounts of and/or poorly designed outdoor lights. Light pollution will not degrade the viewing of the Moon and planets, but it can seriously limit the number of non-solar system objects you might otherwise see (objects such as galaxies, star clusters and nebulae). Light pollution has invaded almost all populated areas of the country. Often, the only remedy is to drive to a dark location, generally 50 to 100 miles or so from any major city (and even at this distance evidence of light pollution may remain readily visible). For more information on light pollution, see my article dedicated to this topic: Light Pollution. For a very comprehensive treatment of light pollution, see the International Dark Sky Organization's web site at http://www.darksky.org.
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Re: Astronomer: Beginner Tips

Postby abuali » 11 Sep 2009, 03:20

Muhammad Mahdi wrote:Thanks for the interesting read.
I remember how nice the craters on the moon looked with my 300mm :D


we should have a thread on photography and on what equipments/camera's ask members use
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Re: Astronomer: Beginner Tips

Postby abuali » 11 Sep 2009, 08:01

Number 3: Use LOW magnification, and make sure your scope is properly adjusted!

  • Most beginning astronomers think that high magnification is they key to great viewing. This is a common misconception. Any experienced amateur astronomer will tell you that most observing is performed using low magnification. For small telescopes, low magnification (or "power") means anywhere from about 20x to about 50x. High power is useful (and often necessary) for viewing planets and double stars. However, initially finding a planet (or any object) is much easier with low power. Even users of large telescopes use mostly low power. The most magnification that is useful in a typical small telescope is in the range of 100x to 200x (for 'scopes in the 6" range). Small telescopes do not gather enough light for satisfactory high power views of galaxies and nebulae. So, resist the temptation to "go to high power"! Stay with low magnification for most objects, and you will see much more!
  • Getting quality images in a reflecting (Newtonian) type telescope is very much a function of the alignment or collimation of the optics (misalignment is common among reflecting telescopes but almost never an issue with refracting telescopes). If the optics are out of alignment, you will still "see" through the telescope, but very likely the images won't focus properly, or the image will seem somewhat distorted. The manuals for telescopes from all quality vendors will include instructions on how to collimate the optics. It can be a bit tricky at first; do the initial alignment indoors (fine tuning can be done outside at night). Collimation tools are also available for around $40 and are a great help simplifiying the aligning the optics. Optics for Newtonian and Schmidt Cassegrain telescopes do need to be checked for alignment from time to time, especially if the telescope has taken a bumpy ride in the back of a car (for example). If you want to eliminate the "maintenance" associated with telescopes, buy a refracting telescope.
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Re: Astronomer: Beginner Tips

Postby abuali » 11 Sep 2009, 08:06

Number 4: Telescope Quality

As far as beginner telescopes are concerned, there are many many telescopes that are best avoided. Fortuntaley there are more great choices than ever before (and at reasonable prices). Expect to pay at least $200 - $500 for a quality beginner telescope. You can find scopes for around $100, but beware. Many of them make performance claims that are preposterous, and are of very poor mechanical and optical quality. You are better off buying a simple (but well made) telescope. In other words, buy a telescope where the money has gone into basic functionality (good optics and a good mount). Telescopes to be avoided are easily identified, since they come standard with numerous (but often useless) accessories!

  • Of paramount importance in any telescope is optical quality. While a beginner telescope cannot offer custom hand made and certified state of the art optics, ones from reputable manufacturers are generally very good. It is generally best to avoid "department store" (Wal Mart, Toys R Us, etc) telescopes. Some scopes available from such vendors have a satisfactory main optic, but most of the time the eyepieces (discussed below) are of marginal quality. The very worst telescopes have plastic lenses... needless to say, these units will have extremely poor performance.
  • Perhaps the second most important part of a telescope is its mount. There are numerous types of mounts (beyond the scope of this article). They key is to make sure the one that comes with the scope you're considering is smooth, stable, and solid. Few things in Astronomy are more frustrating that fighting with a poor telescope mounting in the dark! Poor mountings will make using high magnification especially annoying and frustrating. Purchase a telescope with a simple (but quality) mount.
  • One of the important items that come with a telescope are the eyepieces. The eyepieces allow you to change the magnification of the telescope. Many low end telescopes provide 2 or 3 poor quality eyepieces (many of which result in a magnification well beyond the useful capability of the scope). For small beginner telescopes, it is much better to have one or two quality eyepieces (as opposed to a battery of marginal eyepieces). What is best for a beginner? Look for one eyepiece that produces low magnification (about 30x - 50x) and a second one for higher magnification (about 100x). Eyepieces are marked with letters and numbers; these characters denote focal length (and sometimes the optical design) of the eyepiece. Beware of telescopes that have eyepieces with any or all of the following markings: H25, H20, H12.5, and SR4. If the scope has one or more of these eyepieces, it is likely that the images will be marginal to poor. The "H" stands for "Huygens", one of the poorest performing optical designs available (they are inexpensive to manufacture however). "SR" stands for Symmetric Ramsden. Trust me on this: no small telescope will benefit from an SR4 eyepiece. The manufacturer simply includes this so that the high end magnification of the telescope sounds very impressive (it is a marketing ploy) Most people will find using an SR4mm eyepiece extremely frustrating. The SR4mm eyepiece has what is known as very poor eye relief. If you wear glasses, the SR4mm eyepiece will be impossible to look through. Eyepieces with poor eye relief require that your eye be very close to them, often uncomfortably close even for those who do not wear eyeglasses. The bottom line: Any telescope will have sharper and brighter images when LOW magnification is used. And, finding objects will be MUCH easier!

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