What Can I See In a Telescope
From SkyInsight
By Donald P. Waid
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Introduction
The Hubble Space Telescope has displayed to the world the beauty of celestial objects. The images published by the Hubble team are viewed on television, published in magazines and books, and displayed on the Internet. Awareness of Space and its mysterious and beautiful objects has never been higher. Many aspiring amateur astronomers would very much like to see these wonders through their own telescope but have very little knowledge of just what their views through moderate-sized, and -priced, telescopes will look like. They ask questions such as, "How much can I see looking through the telescope?" "Will I be able to see those beautiful galaxies and nebulas?" "What will they really look like?" "Can I see the colors like those in the photographs displayed in magazines?" In this article I will endeavor to answer some of these questions.
First of all, do not expect to see celestial objects as they are displayed in most photographs. These images are usually acquired with very long exposures utilizing sensitive CCD cameras and much more sophisticated equipment than what is within the reach of most amateur astronomers. This is not to say beautiful views are not possible to see in moderate amateur equipment. They definitely are possible. Many are thrilled (myself included) at the wonderful vistas enjoyed through amateur telescopes.
Just how much can one expect to see looking through a moderate, say 6 to 10-inch, reflecting telescope? Will a nebula be just a fuzzy cloud or will it display form and structure? Will a galaxy have detail or be just a fuzzy patch in the eyepiece? How about the Moon and planets?
The answer to these questions depends on several factors. Some have to do with the telescope being used, the environment one observes from, and the object being observed. Let's explore a few of these factors.
Sky Conditions
Dark skies are very important to visual observation. This is not to say a person cannot do visual observation from badly light polluted skies. I have two observing locations; one in a VERY light polluted suburban location, and one in a small rural community with relatively dark skies. The difference in observations between the two is primarily in the ability to discern faint details. At the risk of becoming too technical, if the background light pollution (sky glow) is the same magnitude as, or greater than, the faint details of the object being observed, then there is no contrast between the background and those faint details. They will not stand out above the background and will not be visible. Rule of thumb, the darker the skies the fainter the objects that can be observed. Many of the objects in the heavens are very bright. The Moon is an excellent example. Many devote all their attention to just lunar observation. The Moon is very bright and light pollution is not a factor. Excellent images of the Moon are easily made with a common digital camera held up to the telescope eyepiece. Lunar observations may be undertaken using small inexpensive refractors or with expensive large aperture reflectors. Other objects that break through the light pollution barrier are the planets. Venus, Jupiter and Saturn are all very bright. Mars, when its orbit brings it close to Earth every two years, is also very bright. These objects are best viewed with high magnifications. Small medium focal length refractors using short focal length eyepieces are very adequate for planetary observation.
Light pollution is only one sky condition factor to consider at your viewing location. Such things as humidity, transparency and atmospheric turbulence come into play. High humidity can be more than a nuisance causing one to get wet walking across a dew covered lawn for the morning newspaper. During the evening while observing in humid conditions this same dew forming on the grass also has a nasty habit of forming on the telescope. The lens "fogs" and until it is removed, your telescope is out of commission. Dew prevention heater strips and other products are available as telescopic accessories, and they work quite well. An alternative to these is the use of a handheld hair drier. When the lens of my telescope fogs, a short application of low heat from the hair drier clears it up quickly. Just remember that the non-astronomical members of the household may be upset if you don't put the drier back after you finish your observing session. Atmospheric transparency can also be a problem. A cloud-covered sky is obvious, but a thin layer of "haze" sometimes is not. If the Moon is up, and you notice a bright, extended, halo around it, the transparency is not good. Other local conditions such as smoke and dust can affect the transparency. Turbulence in the atmosphere can cause problems with what astronomers refer to as "seeing". This is what makes the stars "twinkle". It is also bad for telescopic observations. At higher magnifications the view in the eyepiece will shimmer and sharp images will be difficult to achieve.
The amateur astronomer cannot avoid many of these sky conditions, but they can be tolerated. Less than optimum sky conditions should not prevent one from exploring amateur astronomy.
Telescope Aperture
<p Telescope aperture is important, but sometimes overemphasized. The eye is small and the amount of light it gathers serves us well for our daily life but not so for viewing anything but the brightest stars. We augment our eyes with the use of our telescopes. The larger the aperture, the more photons of light are gathered and sent to our eyes. (More photons, more detail, fainter objects.) I had an eight-inch SCT (Schmidt Cassegrain Telescope) that had very good optics. I then purchased a big 12-inch SCT and thought the heavens would suddenly "open up". Quite frankly, I was disappointed when I looked through the "Big Scope". The difference was there, but it was not like night and day. The bigger scope's display was somewhat brighter and, because of the longer focal length (~ 3000 mm vs. 2000 mm), objects were larger. </p>
Many amateur astronomers get "aperture fever" i.e., an uncontrollable desire for the largest diameter telescope available. One should avoid this pitfall. I know, I have been a victim! My 12-inch SCT is an example. In my opinion, a good starting point is the 6 to 8 inch reflecting telescope or a 5 to 6 inch achromatic refracting telescope. Many of these are available from different venders. Browse the advertisements in any reputable amateur astronomy magazine or publication and compare their products and prices. Avoid buying what we in amateur astronomy refer to as "Department Store Telescopes". These are the telescopes, usually very low in price, displayed with very pretty color images of planets, galaxies and nebulae on the boxes and boasting about how much they can magnify objects. In most cases these are cheaply made with inferior optics and will be of little or no use to anyone interested in exploring the hobby of amateur astronomy.
Observational Skills
Observational skills are important. You must develop good observational skills to fully appreciate the benefits of any scope you are using. Learning to use such skills as "averted vision" and techniques involving moving the telescope slightly to take advantage of the human eye's ability to detect motion are very important for visual observation. An astronomy professor teaching a beginning astronomy course reported that at the start of the course he takes his students to the observatory. He then has them look at a faint object, such as a dim nebula, and asks them what they see. They usually say they see just some stars and nothing else. At the end of the course, after teaching observational skills, he asks them to view the same object and report what they see. They then, if they have been good students, report much more detail, faint areas of nebulosity and subtle differences in brightness of the stars in the field of view. Good observational skills must be learned and are essential to the appreciation of the wonders available to the observer. This is probably the most important aspect of successfully pursuing amateur astronomy.
Enhancement Filters
Eyepiece filters can help bring out details of some nebulae and other deep sky objects by increasing the background contrast and suppressing light pollution wavelengths. They do help, but there is a price to pay. Any filter blocks light in order to perform its job. Blocked light, fewer photons, dimmer objects. A larger aperture scope with a light pollution filter will have a higher contrasting background (darker sky) but now delivers fewer photons to the eye. Roughly speaking, a 12 inch scope with a good light pollution suppression filter in the suburbs would perform like a smaller, say 6 to 8 inch, scope in a rural, moderately dark sky, location. There are many different types of filters. They include different colored filters to enhance planetary views, light pollution suppression filters to cut sky glow, neutral density lunar filters to cut down the glare of the bright Moon, hydrogen beta filters for certain types of nebula viewing and on and on. My advice to those new to amateur astronomy is to avoid using these filters until after basic skills are mastered. The only exception would be the neutral density lunar filter. The Moon can be uncomfortably bright when viewed through a telescope.
Viewing Expectations
In the discussion above I touched on what can be expected when viewing the Moon and planets, even in light polluted urban skies with very moderate amateur telescopes. These alone are more than enough to spend many an enjoyable evening with your telescope. I never get enough of viewing the craters, mountains and plains of the moon. Subtle features such as lunar domes and rilles are exciting to tease out of the eyepiece. Saturn with its rings is one of the beauties of our solar system. Jupiter with its Galilean moons and distinct cloud bands is a wonder to observe. Mars with its icecaps and its ruddy hue is a spectacular sight. It is one of the few objects that will display color in amateur telescopes.
Many wish to go farther than the solar system objects mentioned above. What can one expect to see while observing "Deep Sky Objects"? The answer to this is difficult because it depends on the factors discussed in the beginning of the article. I will try to generalize somewhat and relate my experiences observing deep sky objects.
Star Clusters
Star clusters come in two forms. Open clusters consist of loosely bound stars in a wide and usually irregular gathering. Globular star clusters consist of hundreds of thousands of stars, tightly bound, as in a ball. They are almost like little spherical galaxies but are really part of our own Milky Way Galaxy. Both types of clusters are easily viewed with amateur telescopes. These clusters can be very beautiful to observe. Open clusters remind me of diamonds spread out on jewel salesman's black velvet cloth. M13, the great globular in Hercules, looks like a fuzzy ball with a speckling of ever thinning stars extending out from its bright center.
Nebulae and Galaxies
What one can expect to see when viewing nebulae from a moderately dark sky depends on the brightness of the nebula. The Orion nebula surrounding the trapezium stars stands out very well even in a small telescope, or even large binoculars. It is a very nice object to observe. It is a hit when showing off your telescope to non-astronomical friends. It's almost as good as the Moon! What you will not see is the dim outer portions of the nebula. With moderate sized telescopes (6 to 10 inch reflectors) you will be able to discern the brighter portions of some nebulae. The Ring Nebula, M57, is a favorite. It will look like a small "smoke ring". I have never been able to see the two stars in the center of it even with my 12-inch telescope located in my light polluted suburban location. Even from that location the nebula itself stands out remarkably well and is fascinating to observe. Other brighter nebulae are easily visible from all but the worst light polluted skies using moderate aperture scopes. M27, M16, M17, and others are good visual objects. You will be able to discern the bright parts of the nebula and even some shape detail, but not the faint portions you see in photographs. What you do see is thrilling nonetheless.
Viewing galaxies is much the same as nebulae. The same optical and viewing considerations apply. Galaxies, especially face-on spirals, are spread out and their surface brightness is very low. The Triangulum Galaxy, M33, is a good example. I cannot see it visually from my suburban location even in my 12-inch telescope. It simply is swamped by the sky glow. M81 and M82 do stand out even in relatively light polluted skies. M81 looks like a small elliptical fuzzy object and M82 appears as a small cigar-shaped object. I am able to see these galaxies because they are relatively bright, especially their cores. It was very exciting to see both of them at the same time in a wide-angle, low power, eyepiece! What you will not see is the faint outer portions of the galaxies. In my telescopes, even from darker skies, The Andromeda Galaxy, M31, appears as a fairly bright oval, somewhat fuzzy, object. Depending on the field of view, and if a wide field eyepiece is used, you may also see the small companion galaxies M32 and M110. What you will not see are the faint details such as the dust lanes and outer disk structure.
Color in the Eyepiece
With anything except bright stars such as the red giant Betelgeuse or some of the "carbon" stars and possibly the planets, one should not expect to see color. The color is there and long exposure photographs or CCD images do discern the color, but the color receptors in the eye are simply not sensitive enough to perceive them while observing nebulae or other deep sky objects using moderate or even larger aperture amateur telescopes. I understand color can be discerned in some brighter nebulae using apertures of approximately 25 inches.
In conclusion, amateur astronomy can be a relaxing and rewarding hobby. It can provide a lifetime of enjoyment. One can enter the hobby with limited funds and still expect wonderful vistas in the eyepiece. Less than optimum sky conditions can be tolerated and should not deter one from exploring amateur astronomy. One should also realize that the pretty color pictures on the boxes of department store telescopes are not what to expect in the telescope’s eyepiece. Start with a reasonably good telescope in the aperture range suggested above, don't expect Hubble-like vistas, expend the effort to learn good observational skills, and enjoy this spectacular and rewarding hobby of amateur astronomy.
Source: http://www.waid-observatory.com
Article published on Sky Insight with the author's permission.
