BEGINNING OBSERVERS: WHY USE A TELESCOPE?

Everybody who owns a telescope has heard the familiar question: "How far can you see with that gadget?" The question should be this: "How far back in time can you see with that telescope?"

Our UNAIDED human eye can see very far away and back many years in time. The Andromeda galaxy (Messier No. 31, or "M31"), which observers can just perceive as a faint smudge of light in a very dark sky, is about 12,900,000,000,000,000,000 miles away (its light arrived here 2.2 million years after leaving the stars of the galaxy!)

Some of us can see much farther into space: with an 8" aperture scope you can see a "quasar" which is a mysterious body deep in space in the constellation of Virgo. The light of this "quasi-stellar object" called 3C 273 began a journey to our solar system 3 BILLION years ago!

Even city-dwellers whose night skies suffer from the glow of "light pollution" will be able to use a small 60-80 millimeter aperture scope to see such objects as --

• Our Moon, and at least 6 of the known planets not counting
Earth (except faint 'dwarf planet' Pluto, which requires a
larger scope), plus some of the moons of Saturn and Jupiter.



• Occasional comets, and bright asteroids.




• Interesting stars, many of them richly colored with a variety
of hues, and many bright multiple star systems.

In a dark sky, you can see--

• The rich starclouds of the Milky Way.




• "Galaxies," unimaginably vast collections of billions of stars,
like our own Milky Way, drifting in a common motion in our
expanding universe.




• "Open" Clusters of stars.




• "Globular" Clusters of stars.




• So-called "bright" emission nebulae (though they may not
appear bright in a telescopic view).




• Reflection nebulae.




• Planetary nebulae.




• "Dark nebulae" (clouds of interstellar matter.)




• And we may even see man-made satellites and orbiting rocket engines
which glimmer in reflected sunlight as they tumble!

The skill of finding these objects amongst the astonishing variety of the 6,000 naked-eye stars will grow as long as you observe the heavens. Unfortunately, only the Moon, some of the planets, and the brightest star clusters will appear really vivid in your telescope if you use it in a city environment where there are lots of streetlights. To see galaxies and nebulae and other dim celestial objects, take your scope away from city lights. Turn off all lights around you, and wait a few minutes until your eyes adjust to the dark. Then, you'll see much more in your telescopic view of the sky; but don't be disappointed: the colorful nebulae that you see in photographs will all look pale gray to the eye. The brightest stars, and some of the planets, may show traces of color, especially in larger scopes.

THE BEGINNER'S OBSERVING SESSION

Always set up a new scope first during the day to become familiarized with its adjustments, but DO NOT POINT IT AT THE SUN, or you might cause damage to the instrument, set a fire, or burn or blind yourself!

It is important to know HOW to look into a telescope. The eyepiece concentrates an image of the light entering the telescope's front aperture, where the scope is pointed and where light enters. Just outside of the eyepiece -- above the 'looking end' -- an exit pupil is formed: a small circle of light that is the image seen by the telescope aperture. You should place your head so that your eye is just at this spot in order to see the entire field of view.

Point the telescope at something in your neighborhood that is at least four or five houses away, not close to you. Position yourself so that your eye is about a quarter- to a half-inch away from the top of the eyepiece. You should be able then to focus the image and see the whole field of view: adjust the focuser until the image of the object or light you are viewing is sharp. The distance from the end of your eyepiece to your eye will vary a bit, with different eyepieces.

Start experimenting with the one you own that has the longest focal length (largest number: such as "25", for "25 millimeter focal length") which will give you the lowest magnification and make it easiest to see something clearly.

At left, Regina is shown pointing her own telescope. When she has found the right spot, she will let go of it for viewing: don't hold on to the telescope while you observe. The image will bounce around if you touch or shake the telescope or tripod. You might like to lean on a chair, ladder, or a tree while you observe.

Preserving your "Night Vision"

Your eyes have two modes of operating: "day vision" adjusts to bright scenes and gives the sharpest images and best color rendition. "Night vision" is for seeing in the dark, and shows very little color, but allows you to see dim objects. It takes the eyes about a half hour to adjust from day to night vision, and the process is called "dark adaptation". You will get your best views of deep sky objects through your telescope when you have dark adapted your eyes: by waiting, avoiding bright light, until they are the most sensitive.

You may not have to do this if you want to take your telescope outside and look at the bright Moon and planets: with "day" vision, you might see the finest details. But to see faint stars, galaxies, and nebulae, you MUST dark adapt your eyes, or what you see in the eyepiece of your scope or binoculars might be disappointingly dim.

There are ways to achieve and preserve your night vision that are simple and inexpensive, or even free. You can put a dark cloth over your head: don't feel silly! Some of the greatest astronomers learned to do this, like the famous William Herschel. You may get a small black eye-patch at the drug store for a few dollars, and wear it over the eye that you prefer to use for looking through your scope: take it off only when you wish to observe. Or, you may purchase an inexpensive gadget from an astronomy products dealer that is remarkably effective: it is called "Astrogoggles", and is a deep red filter that will block all other color wavelengths. By restricting your vision to red light you may speed up the dark adaptation process.

We began to use this marvelous product when it was first introduced in the 1980s (you may find it at this retail dealer, for instance) and were privileged to be provided with an article about how it was developed, and how the eye functions when viewing dim objects: written by the product's developer Kevin Fly Hill, it is an advanced discussion for scientifically-minded readers that we are pleased to present in "Eyepiece" and on our website.

During your deep-sky observing session, if you need to illuminate something -- your charts, books, or equipment -- be SURE to use only a red light, not a white one! Or, put on your Astrogoggles.

Telescope Numbers

The "Eyepiece" program will calculate things you need to know about your telescope, but to do this, you must know TWO important values:

APERTURE SIZE: This is the diameter of the main telescope objective lens or mirror; our program will use either inches or millimeters;

Either the:

FOCAL RATIO (the focal length divided by the aperture); or

FOCAL LENGTH: the distance from the main objective lens or mirror to the "focal plane" where the eyepiece is installed;

This information will usually be found on a small metal plate on your telescope, or in the owner's manual. The diagram below shows the interior of a Newtonian reflector telescope, illustrating the light path and where the aperture and focal length are measured.

"Eyepiece" will use these numbers to be able to tell you what magnification and field of view are provided by your specific eyepiece's image. It will tell you what eyepiece focal length is required for a specific magnification. Or, it will calculate magnification if you tell it what eyepiece focal length you are using.

Telescope Types

There are numerous kinds of telescope designs, but the most common ones that are owned by most amateur astronomers (shown in a picture below the following explanations) are these:

• Refractor Types: the first telescope design of them all, based on the use of an objective lens to focus the light. You must make sure that the objective lens is an achromat design at the very least, for then it will have the minimum amount of "false color" (chromatic aberration.) Some of the cheapest "department store scopes" use ordinary single lenses, and produce image quality that is sub-standard and blurry, not useful for astronomy. The latest types of high quality refractors use a special apochromatic lens with even fewer aberrations than the achromat type (but, they are relatively costly.)

Small refractors are ideal types for beginners, as long as they are made well, have a lens aperture size at least 60mm in diameter (the larger 80mm size is more efficient), and come with good eyepieces. The cheapest and poorest ones are often sold on the basis of "high power" and claim "600x magnification": avoid those! Buy a good astronomical refractor from an amateur astronomy products specialty dealer. You should be able to get a usable one for $200 or even slightly less.

Refractor telescopes usually come with an adaptor (called a "diagonal") that makes the image you see "right side up" (though it might sometimes be reversed, left-to-right.) Such types of scope are, therefore, useful for daytime viewing.

• Newtonian Reflector Types: A very simple design that is very old, using a "parabolic primary mirror" coated with aluminum to gather, reflect, and focus light. There is no "false color" or chromatic aberration, and because mirrors are cheaper to make than lenses, you can get a larger aperture, and thus look 'deeper' into space, with brighter images, than with a comparably-priced refractor telescope. There is one important optical aberration to watch for: "coma", which is an inherent quality of the design of a "fast" (short focal ratio: i. e., about f/4 or f/5) mirror. The "faster" the mirror, the more coma distortion it will have: then, stars away from the center of the field of view become elongated (and look like little 'comets'.) Some eyepieces can correct this defect. "Slower" focal ratio mirrors (about f/8 to f/10) have less coma, with cleaner stars away from the center of the field. But those types of scopes have intrinsically narrower fields of view, and yield higher magnification with a given set of eyepieces than scopes with "fast" mirrors. ("Slow" and "fast" are terms that date from early photography, and are not related to the eye's perception of image brightness, as the eye does not work like photographic film.)

Newtonian reflectors require attention to their optical alignment from time to time (called "collimation"), which will be explained in the manual for any good one (and online in many website articles, such as this explanation by Philip Hoyle.) Reflectors should be put outside in ambient air to cool down for a while, before use, in order to get the sharpest, clearest images.

Newtonian reflector telescopes produce an image that is upside down and reversed left-to-right: this is useful for astronomy but can be very confusing if you intend to look at the Earth during daytime.

• Compound Reflector Types: Many amateur astronomers have either a "Schmidt-Cassegrain" reflector telescope, or a "Maksutov" reflector, two designs that have advantages, particularly for photography and planetary viewing. These designs 'fold' the light path into a smaller package than regular Newtonian reflectors, but require more optics to achieve this, consequently costing much more. While not the ideal type for beginners, the compound reflector is often constructed to very high optical standards, and is sought by advanced users.

These types of telescopes may be equipped with a "diagonal" to provide right-side-up images for daytime viewing, though the magnification is sometimes rather high for such purposes.

Here is an excellent, in-depth webpage about telescope types, produced by Randy Smith. Below is our simplified chart of the basic designs discussed.

Telescope Mounts

Most beginning telescope types will come on a mount that is one of a few basic types:

• Alt-Azimuth: This simple design allows the telescope to revolve horizontally (in azimuth) and up/down in altitude, abbreviated "alt-az." Dobsonian reflector telescopes use such a simple, inexpensive, trouble-free mount, and are perhaps the easiest type for beginners to understand and use. The drawback is that they do not "track" with the apparent motion of the sky, and so cannot be used for photography. Regina Roper is shown above, in the section discussing "The Beginner's Observing Session", looking through her little 4" aperture Orion "Starblast" reflector telescope: it uses an alt-az mounting.




• Equatorial: The beginner refractor telescope shown at the top of this article -- and the little table-top mount shown here -- features a "German Equatorial Mount", based on a design dating from the early 1800s. This type of mount permits the telescope to rotate in correspondence with the apparent motion of the sky, which is accomplished by rotating the right ascension axis. With optional motor added on that axis, it will hold the celestial image steady. Adding also a motor on the declination axis will permit guided astrophotography. Motorized equatorial mounts are easiest to use at high magnification for looking at details on the planets. The drawback is the increased complexity, cost, and learning curve.




• Fork Mounts & "GOTO" mounts: Short telescope tubes of the refractor or compound design may often be used on a "fork mount", which can be built either as an alt-az, or an equatorial, type. These mounts have recently been adapted by manufacturers for computerized pointing and tracking, using motors that are driven by electronic processors running software programs that know how to point them at celestial objects. Such a system is called a "GOTO" scope, for it is capable of 'going to' an object after receiving the computerized instructions. A related type is the "PUSHTO" scope, which does not have tracking motors: the user looks at a digital readout device, which after calibration "knows" where the scope is pointed, and will show the observer how to direct it to a desired celestial object.




A very nice, illustrated website about telescope mounts, produced by Jim Harris, will take you to the next level of information.

Eyepieces

Modern eyepieces are made with a remarkable variety of designs, some costing more than a good intermediate quality 10" aperture Newtonian reflector scope! You are lucky to be starting with amateur astronomical observing these days: now, beginner telescopes are likely to be equipped with one of the very best design types: the Plössl (pronounced PLOSS-el), which gives sharp images over a fairly wide field of view. The illustration below shows how the internal elements in standard designs are often arranged. If possible, try to avoid the cheap, simple eyepieces that used to come with beginner telescopes: "Huygenian" or "Ramsden" or "HMA" types may have an intrinsically narrow field, and often do not work well on "fast" reflector scopes. Some typical astronomical eyepiece types are these:

• Kellner Types: This design is now virtually obsolete but occasionally beginner scopes have Kellner eyepieces in long focal lengths. Some makers call them "modified achromats." These are usable but are not considered desirable by experts: the field of view is somewhat narrower than optimal. (35 to 40 degree apparent field of view)

• Orthoscopic Types: This old design is often considered by advanced planetary observers to give the very sharpest focus at high magnification. (40 to 45 degree apparent field of view)

• Plössl Types: A high quality Plössl offers superbly crisp, high contrast images over a reasonably wide field of view, working well in any type of scope. (43 to 52 degree apparent field of view, typically)

• Erfle Types: Yielding a much wider field of view than the above designs, the Erfle is prone to "edge distortion" when used in telescopes with low focal ratios, but may give good performance in "slower" (say, f/8) refractors, or in compound reflector telescopes. (60 to 68 degree apparent field of view, typically)

• Wide Field Types: Using many glass lens elements, these designs are more expensive but yield in some models the widest possible fields of view, and may even be designed to correct for the coma of fast reflectors. However, they are costly and one need not start out with them when getting introduced to astronomical observing. (Greater than 68 degree field of view minimally, to about 82-85 degrees apparent field of view maximally.)

The phrase "apparent field of view" describes the intrinsic angle of the cone of light that the eyepiece can deliver to the eye: a nice illustration of this is shown on this webpage by Matt Oltersdorf. The "true" field of view, on the other hand, is the ACTUAL field width as seen when the eyepiece is used in a given telescope. Our program EYEPIECE calculates this, but only as a mathematical approximation: thus we call it the "Approximate Visual Field", which will vary as you change the telescope focal length and focal ratio. For more information, check the EYEPIECE manuals and help files. You may also be interested in this in-depth Wikipedia article about eyepieces.

Eyepieces are addictive! The more you own, the more you will want to get to "fill in" some small difference in focal length, or to upgrade to better types. We suggest that you need to start with focal lengths that will yield four basic ranges: low, moderately-low, moderately high, and high magnification. Four eyepieces will cover the essential range; or three eyepieces and a 2x Barlow adaptor.

The reason we did not give numbers in the above paragraph is that values will vary with each telescope's specific focal length and focal ratio, and aperture diameter. Generally, the lowest power you will be able to use efficiently will be 3 power per inch of aperture, to set the "low" end. The highest power will probably be somewhere between 40 and 50 power per inch of aperture for scopes up to about 8 inches of aperture diameter. Use our program EYEPIECE to calculate the focal length values you will need to obtain. Try to space the magnification range fairly uniformly. For instance: you might need to purchase eyepieces in the focal lengths of 35mm, 20mm, 9mm, and 6mm. If you then get a 2x Barlow (which multiplies the magnification two times) you can "fill in" the range without duplication: 35/17.5; 20/10, 9/4.5, 6/3 mm focal lengths.

Does the author have enough eyepieces and filters? Certainly: but he still believes he needs one more...

FINDING CELESTIAL OBJECTS WITH A STAR CHART

At the left, here is part of a star chart for a region in the constellation Orion near the star Alnitak. To use a star chart at night, get a red flashlight, not a white light one. Red light won't keep your eyes from being sensitive to faint star light, but bright white light will reduce your ability to see dim views.

Using a star chart of the appropriate constellation, compare the stars you see with your naked eye to the printed chart, correcting its orientation to agree with the sky. Next, use binoculars (5 X 35 or 7 X 50 models work well) to get a narrower-angle view. Aim your telescope's "finderscope" (usually about 6 or 7 power, with a 30 to 50mm aperture objective lens) at the object desired. Or, utilize a "reflex" non-magnifying sight, like the famous Telrad™, and place the object within the inner red illuminated circle of light.

Only now should you look for the object in the main telescope eyepiece lens. Use the lowest-power eyepiece with longest focal length in millimeters. You may have to re-orient your star chart or observing guide if your scope optics rotate or invert the image; consult the scope manual for information, or check the scope with a daytime view.

Our program EYEPIECE will show you the estimated visual field of view of all your eyepieces, so you can predict what power/field of view to use to fit your desired object into the eyepiece view. If you observe in a light-polluted sky, or desire greater contrast when viewing nebulae, use EYEPIECE's recommendations for employing "LPR" (light pollution rejection) and Nebular filters with the correct exit-pupil range.

When looking at a faint star or nebula, it is important NOT to stare at a fixed point. Let your eye drift back and forth across the area of the object you are trying to see. If the object is faint, you may see it better if you DON'T look directly at it! Use "averted vision" by glancing slightly toward the direction of your nose, to move the image to the area in the retina where there are more "rods" for detecting faint light.

The bright planets might seem easy to observe, but, like all objects in the sky, are clearest when they are high up and away from the horizon. Venus is spectacular, so bright that it may twitch and twinkle with flashes of color caused by the layers of air in our earth's atmosphere. Mars is often too far away to be clearly visible; Jupiter and Saturn are a wonderful treat during the appropriate yearly seasons, and will have a trace of color: Jupiter may show a bit of pale green and blue, and in telescopes able to gather enough light, Saturn will look yellowish.

Jupiter and moon Io; Saturn; Mars: digital images taken by S. Waldee

Galaxies and nebulae can be hard to spot in a small telescope. Often they appear no more detailed than small fuzzy smudges of light. Multiple stars like the "Trapezium" system in the mouth of the beautiful Orion nebula, or collections of stars like the "open cluster" called The Pleiades will fascinate with their apparent geometrical relationships that we create in our minds. Some individual stars have brilliant colors, like red Antares, blue-white Vega, or yellow Capella.

Trapezium of M42, Pleiades by Chuck Vaughan; Rho Ophiuchi Region by Adam Block, KPNO Visitor's Program

Unfortunately, the dim light of nebulous celestial objects is too faint to be seen by the eye in color through an amateur sized telescope. Film and digital cameras can detect color, which takes time to build up in long exposures. The eye, however, does not work that way. Light must be sufficiently bright for colors to be seen. Because of this, some bright stars will indeed have various shades of color, ranging from pinks to light purple and blue.

Globular clusters may seem to resemble small fuzzy patches, while the brightest of Messier globulars may sometimes be "resolved" into many individual star images with very good telescopes of 3 - 4" aperture.

"Dark Nebulae" or the dust-lanes in many deep-sky objects like the "Lagoon Nebula" block some or all of further-distant sources. "Bright" nebulae either emit photons, or reflect light scattered off dusty clouds in space. To be able to see the widest light-to-dark contrast ranges, use an appropriate exit pupil size (see the Definition files for details) as shown by the program EYEPIECE. Carefully dark-adapt your eyes by avoiding any lights except the stars or a faint red flashlight.

Messier 17 nebula: (left) light polluted sky; (2) dark sky view; (3) color photo

And, remember: to get the best views of the faint nebulae or galaxies that can be shown by your telescope, USE A DARK SKY SITE for viewing, not a bright city sky with lots of streetlights. Telescopes will teach you a lot about the lovely objects in the night sky, but as long as you understand that your small amateur telescope won't be able to make celestial objects look as bright and clear as giant telescopes -- or ones orbiting the Earth, above our dense atmosphere -- then you can have a distinct thrill, knowing that the sight you're seeing is REAL... nothing stands between you and the experience of seeing the actual cosmos!

MAGNIFICATION and "SEEING"

An important thing to remember is not to use TOO MUCH magnification! Sometimes beginner telescopes are sold on the basis that they have "600 POWER" or other such high magnifications. But, only a gigantic telescope can use that much magnification and still have a clear, sharp image. A small amateur telescope -- say, 2 to 6 inches of aperture -- will always look best when used at low to moderate magnification. Start with 20x and go up from there. Star clusters, the Milky Way, the Moon, and many objects look fine at low magnification: they'll be sharper, clearer, and have higher contrast than at high magnification. Using too much power will do two things that will not be good for your observing: (1) images will be dim and blurry with power that is too high; and (2) the field of view will be so narrow that it will be hard to point and operate your telescope.

But, planets don't have much detail unless you can go to 100x or higher. And you can use high magnification on the Moon to see detail of the craters and other markings. Always start with the low power eyepiece to find your object; then change eyepieces one step at a time until your image is most satisfying.

A star cluster, (L) blurry & dim:- too much magnification; (R) sharp & clear in wide field, low power view

Astronomers have a term -- the "seeing" -- to describe the quality of sharpness and clarity of what you observe in the night sky with your telescope. Our atmosphere is actually a dense and fluctuating pool of gas molecules though the naked eye can't perceive that. But if you magnify a small region of clear space many dozens of times, and look at a distant object -- a star or planet -- then you'll notice the constant flickering and waviness of the image, caused by the turbulent air. Thus, the "seeing" can be an important aspect of your observing success. In the winter or during stormy weather, the air is likely to be very turbulent, giving shaky and wavy views. During the northern hemisphere's summer or fall, the air may be steadiest, revealing details that are blurred at other times of year; or you can have good or bad seeing almost ANY time, unpredictably! The picture below of the Moon was taken by means of our 11-inch aperture Celestron telescope, and the time of each exposure was 1/20th of one second. The image on the left was captured during a moment of blurred seeing; the one on the right was taken just a few seconds later, when the air was momentarily still. If you had been watching "live" you would have noticed a constant wavering of the image's sharpness. Often when you use about 100x or higher magification you will notice this, and will get only momentary glimpses of clarity: a normal circumstance, and one which "planetary observers" learn to appreciate, waiting patiently for the best moments of distinctness.

If the sky is turbulent and your view is very blurred, reduce the amount of magnification; or in some cases, look at different objects: large, wide ones -- such as big clusters and nebulae -- instead of narrow 'tiny' ones like planets. Not every time you use your scope will the planets look sharp and clear: this is a normal experience. Eventually you will learn to be able to estimate your chances of success based on the weather, and what you can see with your naked eye: if stars are horribly "twinkly" then the planets or the craters of the moon will be very blurry at high magnification.

A useful animated GIF file simulation, on Robert English's website, illustrates the atmospheric turbulence -- variations of 'seeing' -- affecting a highly- magnified view of a star image. When the seeing is as bad as the far-right image, you might as well put away your telescope, or at least use only the very lowest powers of magnification.

Once you have determined how to use your telescope, and are enjoying views of celestial objects, planets, and the Moon, why not try drawing what you see? We have made up a separate web page about it that will help introduce you to this fun and informative activity.

To get the most out of any astronomical telescope, you need good reference works. In addition to utilizing EYEPIECE, you should equip equip your "observer's kit" with at least some of these resources (all of which the author has owned, read, and used, and which continue to offer the best value in their categories, while competing products come and go):

GENERAL PRODUCT ADVICE

STAR WARE, by Philip Harrington - John Wiley & Sons, 242 p., softbound. How to select astronomical equipment: scopes, eyepieces, filters, star charts, all types of accessories. Highly recommended! Be sure also to read Phil's monthly ASTRONOMY Magazine column, "Phil Harrington's Binocular Universe," and look at the articles on his website.

Binoculars are useful tools for every astronomer, and in some cases may be the only way you can enjoy very large-diameter celestial vistas, such as the biggest star clusters. Most of the Messier objects may be spotted in good binoculars in a dark sky. "Astronomical" types have high efficiency due to the size of the "exit pupil" of light that is presented to the eye: 5 to 7mm is desirable. Calculate this by dividing the aperture by the magnification. Therefore, a 7 x 50 binocular (meaning 7 power with 50mm aperture) has an exit pupil of 7.14mm, which is desirable. A small compact bino of 7 x 20 will yield an exit pupil of 2.85mm, which will be very dim when used to view the night sky. Read more about choosing binoculars in this excellent Sky & Telescope article by Ed Ting.

BEGINNER LEVEL RESOURCES

The Web

The Peoria Astronomical Society has put together an excellent beginner tutorial written by John Barra. The topics include learning the sky and constellations; the solar system objects; learning to star hop; planning an observing session; and doing a Messier marathon. The articles are short and concise, and though they are not very 'colorful' in writing or graphics, contain solid information.

The Tutorial Pages on Stephen Tonkin's "Astronomical Unit" website contain succinct articles, and an excellent glossary, that should be used as a reference for high school or adult astronomy beginners. Topics about the science of astronomy include cosmology, the understanding of the heliocentric planetary system, redshift and the scale of the universe, stars and other objects, and celestial coordinates. Amateur telescope topics include polar alignment, star testing, collimation, Barlow lenses, and buying starter telescopes. Good graphics are provided when necessary, but there is a minimum of flashy web-gimmickery, and a maximum of reliable content.

Joe Schlatter, Jr.'s Astronomy Page is a well organized and interesting read, showing how an adult beginner started out: he made some very good decisions along the way, and reports his experiences in a very informative fashion.

It is important for beginning observers to realize that they may not necessarily be able to see the faintest possible things when starting out as a novice telescope user. It is probably necessary to develop the skill to be able to interpret what you see in your eyepiece view as being meaningful, not merely an accidental light reflection or a visual illusion. A good article that may advise you is found here, written by Alan McRobert of Sky & Telescope Magazine. In the section "The Fine Art of Observing", Alan explains many of the issues related to why celestial objects often appear as mere "faint fuzzies": the small bits of light that are rendered by an amateur telescope. Alan's followup article, here, provides more specific details of what you'll do in a typical observing session in order to see, for example, the Messier objects and planets.

Publications

Collins Gem Stars, formerly "Collins Gem Guide to the Night Sky" - Smithsonian. A tiny but surprisingly useful book of star charts, full of facts about the most interesting and generally brightest deep-sky objects. Related: Collins Pocket Guide to Stars and Planets.

The Edmund Sky Guide, by Terence Dickinson and Sam Brown - Edmund Scientific. For high school and older ages: a concise, invaluable guide to celestial coordinates and time-keeping, the constellations, basic telescope optics, and interesting sky objects. Excellent lists of objects.

Celestial Sampler by Sue French, the "Deep Sky Wonders" columnist for Sky & Telescope magazine, is a very elegant compilation of 60 of her "Celestial Sampler" columns, suited to beginners with telescopes of 3" to 4" minimal aperture: each chapter is a celestial tour of an interesting region of the sky, featuring six or more items: including galaxies, double stars, and nebulae that you can easily find and view with inexpensive optics. The writing level is not for the youngest children, but is clear and intelligible, and should be comprehendable to beginning astronomers of about middle school-high school age, on up to adulthood. Sue's introduction to observing is especially valuable. Adults who are new to astronomical observing will love this marvelous book!

FOR ASTRONOMERS OF ALL LEVELS

Everyone needs a planisphere, a handy indicator of the sky's position at any hour throughout the year. There are two that you are likely to find at most dealers: we prefer the Night-Sky model, with dark stars on a light background for easy nighttime readability. The other widely sold brand is the Philips Planisphere, often found in bookstores that carry astronomy publications (and sometimes packaged with a one-sheet star chart and small paperback constellation guide, as the "Stargazer" combination.) Be sure to get one that is rated for your latitude.

Orion DeepMap 600 is a flexible, inexpensive, water resistant single sheet sky chart, with cartography by the famous Wil Tirion, and celestial objects chosen by deep-sky maven Steve Gottlieb, a legendary northern California amateur observer. Even advanced amateurs own this handy resource. Our only disappointment: sometimes there aren't quite enough field stars for hopping to hard-to-find, small diameter objects. But, what else has THIS MUCH great astronomical information in such a compact format?

Sky & Telescope's Pocket Sky Atlas is a new product that, for many people, may be the ideal basic small scale sky atlas: a handy book form with spiral binding, allowing the pages to open flat, sized only 6 by 9 inches but printed with absolute clarity and readability. Unlike the Sky Atlas 2000 (which does show more stars) this new atlas features handy constellation 'stick figures' which even help advanced observers navigate. 1,500 deep sky objects are plotted; the heavy paper pages are treated for water resistance; and colors are chosen to show up in high contrast with a red flashlight. The price is only a few more dollars than the one-sheet Orion DeepMap 600, mentioned above, and (unlike Orion's map) there are the necessary guide stars in profusion, for easy star-hopping. However, the DeepMap600 does show all the stars of a constellation in full, recognizable patterns, while the Pocket Atlas often breaks the constellations between charts: so these two resources might work well together.

The Peterson Field Guide to the Stars and Planets, Jay Pasachoff - Peterson's Guides. In the tradition of the Peterson's nature guides, this volume is a compact reference for naked-eye, binocular, or telescopic sky-watching, though it should be complemented by a full-sized star chart. The DeepMap 600, above, however, is more useful for locating constellations and objects, though the Peterson Field Guide has an amazing amount of data and information for such a small volume.

Web resources for beginners may be found, along with our own favorite celestial reference pages, photographic and digital image sites, and advanced observing web articles, in our own personal list of recommended Internet astronomy links.

INTERMEDIATE TO ADVANCED LEVEL RESOURCES

(a) More Advanced Star Charts

The Sky Atlas 2000, by Tirion - Sky Publishing. The most universally used sky atlas, with 26 large-scale charts of the constellations, containing over 40,000 stars and about 2700 deep-sky objects. Convenient and highly accurate! But, be SURE to complement it by getting the volume "The Sky Atlas Companion" by Strong & Sinnott, which 'unlocks' the data so that you can look up and locate the page for any of the objects plotted in the atlas.

Uranometria 2000.0, by Tirion, Rappaport, and Remaklus (2 Vols., Northern and Southern Hemispheres.) - Willman-Bell. The finest advanced observers' general-purpose star charts in two hardbound volumes; both necessary for viewing all constellations visible from US latitudes. Over 280,000 stars are plotted to 9.75 magnitude, with more than 30,000 deep-sky objects that can be seen with scopes up to 17 - 20" aperture in dark skies.

The Deep Sky Field Guide to Uranometria 2000.0, by Cragin and Bonanno - Willman-Bell. Companion volume to the Uranometria, with every non-stellar object on each chart listed by category, and the latest data of both visual and photographic magnitudes (including surface brightness of many objects) for improved accuracy in discerning objects visually in an eyepiece field.

(b) Guides to Solar System & Deep-Sky Objects

Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System by Robert Burnham, Jr. (3 Vols., hard/paperback) - Dover. Robert Burnham's three indispensable volumes provide a wealth of detailed information covering most of the interesing objects visible in an amateur telescope. A unique, literate, and exhaustive work of extraordinary merit (but with the one shortcoming that all the celestial coordinates are referenced to 1950, not 2000 as in virtually every other modern resource.)
Observer' Handbook 200x, Edited by Roy L. Bishop - Royal Astronomical Society of Canada, University of Toronto Press. The authors of this program find each volume of the best amateur astronomer's ephemeris -- newly issued every year -- to be superior to monthly listings in telescope magazines. A handy, inexpensive, and voluminous source of information!

Observing the Constellations, by John Sanford - Fireside/Simon & Schuster. The observing guide that is one of the favorites of this program's author since 1989 is the delightful work of California professor and astrophotographer John Sanford, featuring constellation lists of galaxies, nebulae, and multiple stars; attractive and readable layout; and superb photos. Deep experience and enthusiasm are evident in each chapter. There are two shortcomings, however: first, the book is out of print (but we've easily found copies online at very low prices); and second, the Tirion charts for each constellation are not detailed enough to be useful on their own: you will still need to augment them with a separate star chart.

Touring the Universe Through Binoculars, by Harrington - Wiley. Of the numerous books about observing with binoculars, we find Harrington's detailed but entertaining volume to be highly comprehensive. However, no charts are given for finding the objects, which are grouped by constellation. Use at the very least the Sky Atlas 2000 in conjunction with a good pair of 7 x 50 (or larger) binos.

The Stephen O'Meara "Deep Sky Companions" series is highly commendable for all but the most experienced observers (but even some old-time experts will enjoy refreshing their knowledge and spending time in the company of this delightful enthusiast.) Three volumes are published by Cambridge University Press: The Messier Objects, The Caldwell Objects (a compilation of deep sky objects chosen by famous writer Patrick Caldwell Moore), and The Herschel 400 Observing Guide.

Also from the admirable series of amateur astronomy books published by Cambridge: David Levy's Guide to the Night Sky, and David Levy's Guide to Observing and Discovering Comets by the American amateur who has discovered more comets in recent times than anybody working as a non-professional astronomer. Levy combines the intellectual authority of a long-practiced expert with the passionate wonder of a child first discovering the night sky's beauties.

The Moon Observer's Handbook, by F. W. Price - Cambridge. An excellent choice for serious study of the moon with a typical amateur scope, featuring a tour of nightly views available from new to full moon. In 1994, Cambridge published Price's equally-fine work "The Planet Observer's Handbook".

Deep-Sky Wonders by Walter Scott Houston (309 pp., paperback, Sky Publishing, 1999) gathers together many of the most interesting segments of many years of "Scotty's" great monthly Sky & Telescope columns about observing. A true poetic lover of the skies, Houston crafted eloquent prose that was unique. He was also an eagle-eyed and perceptive explorer who always brought a new, interesting, and often surprising insight to the discussion of every object that struck his fancy. Indispensible!

(c) Telescope Optics

All About Telescopes, by Sam Brown - Edmund Scientific. Even more useful to advanced than beginning observers is the somewhat out-dated but generally fascinating and exhaustive collection of data, descriptions, tables, and charts of observing and optical info. Amusing and entertaining by reason of the incredible line drawings of the author, half-way between precision blue-prints, and cartoons!

Telescope Optics - A Comprehensive Manual for Amateur Astronomers by Rutten and van Venrooij; 374 pages, hardbound, Willman-Bell. This is the classic modern work, respected by all amateur telescope makers and experts. It is useful for intermediate to advanced astronomers, and for adult beginning telescope makers who have technical skills and acumen but need in-depth information and guidance.

(d) Observing Techniques

Unfortunately, the book we used to recommend -- Visual Astronomy of the Deep Sky, by Roger N. Clark (Cambridge University Press and Sky Publishing, 355 pages, Cambridge, 1990) -- is now out of print. We have found that used copies are being priced by Internet dealers from $150 to $600! Unlike many other books on observing, this scholarly effort was produced by a professional astronomer -- Dr. Roger N. Clark -- who is also a highly-sophisticated amateur visual observer. The informative specifics about human optics and perception were here given for the first time in a popular work. Dr. Clark has a web page about the book, containing some updates and further information. We hope it is republished: and soon!

(e) Astrophotography

The website of Sky & Telescope magazine has two invaluable articles (here, and here) that will provide suggestions for a starting-off point to begin taking pictures of the planets and deep-sky objects with your telescope, referencing today's digital imaging techniques. Then, these books below will continue your education:

"Astrophotography for the Amateur" by Michael Covington. (2nd Edition, 2004) The best of the basic beginner books, with enough information to start the astrophotographer on the path to evolving his or her own successful techniques. Michael's website also features his other admirable books, "How To Use A Computerized Telescope" and books about using digital SLR cameras for astrophotography.

"Introduction to Digital Astrophotography - Imaging the Universe with a Digital Camera" by Robert Reeves (448 pp, hardbound, Willman-Bell) is as thoroughly authoritative as works by this renowned author -- an astrophotography "old timer" -- for using the old chemical photo process effectively. Complements to this book are Reeves' "Wide-Field Astrophotography", and "Introduction to Webcam Astrophotography — Imaging the Universe with the amazing, affordable webcam", quite affordable, and may be indispensible if your interest runs to preserving what you can detect with your telescope.

"A Manual of Advanced Celestial Photography" by Brad Wallis & Robert Provin. (388 pp., hardbound, Cambridge.) How can you not love a couple of astrophotographers with the sense of humor of this pair? Yet, they have written the most readable and engaging book on the subject that also includes advanced techniques as well as formulae for the mathematically-inclined. Wallis & Provin have proven their mettle with photos (published in leading magazines) that confirm fully their opinions! The techniques discussed are only contemporary up to the publication date of 1988, and thus do not cover modern digital astro-imaging by means of DSLR's and CCD's.

"Introduction to Observing and Photographing The Solar System" by Dobbins, Parker, and Capen (215 pp. hardbound.) This older volume, dating back to the 1980s, does not deal with digital imaging, which has revolutionized planetary picture quality, but has an enormous wealth of valuable information that enables the amateur to understand the particular requirements of sky, scope, and instruments to photograph the planets. Any reader of the two leading popular astronomy magazines -- or visitor to national amateur astronomy conferences -- has likely been introduced to the artistry (not to mention the warm personality) of Dr. Donald C. Parker, the amateur member of the team that authored this outstanding volume of helpful information. Parker, a dentist by profession, is America's leading amateur film and CCD planetary photographer. He was guided by the book's other authors, Dobbins and the late Charles Capen (formerly on the staff of Lowell Observatory, long renowned for its planetary photography and research.) The ultimate guide to that most exacting of astrophotographic tasks: taking sharp, clear photos of the planets!

(f) Software Programs

We have been familiar, in recent years, only with Windows™ programs. While we do not necessarily use all of these currently, we have experience with, and respect for, the following, not necessarily in order of merit:


Beginner's Software


Starry Night EDU 2.0 for Grades K-8 is designed for schools, but is also useful as an introduction to families for home use. (And, if you buy a telescope from some dealers, such as Orion Telescope Center, you may receive free software with your new scope, such as the "Starry Night Orion Special Edition" or other comparable offerings.)

Discontinued and long forgotten, "Where the Stars Are" is a Windows 3.1/95 era star chart program that had the same user interface and elegant simplicity as the old Version 3 of "TheSky": years ago it was provided free with new scopes by Orion. We think that this is an exquisitely simple, understandable, and effective program (and so does this critic): it's no longer available but maybe you can be lucky enough to find a copy.

"Eyepiece" 2.0 is an old program -- written for DOS -- that the authors of this website wrote and started to market in 1992. Now we give it away absolutely free at no cost or obligation. It will run as a DOS application in Windows™ and may be of use as you learn to deal with the numbers of amateur astronomy, telescopes, and eyepieces. It will also help you determine a prediction of visibility of many deep sky objects: define the type of scope you own, and your sky darkness, and use the object database to see how the program predicts visibility (on a scale of five categories, from bad to good) and what eyepiece or filter it might suggest. There are other resources and functions in the program for more advanced observers.


Intermediate & Advanced Software


Starry Night: an extremely graphically-elegant work, which is highly demanding of very good, modern computer hardware (including Open-GL video.) Benefits: exceptionally fluid and intuitive interface and operability, and exquisitely realistic reproduction of the night sky, with good resources for planning observing sessions. Comes equipped with the excellent ASCOM telescope control system. Shortcomings: requires excellent, state of the art graphics card and lots of memory and somewhat fast CPU speed, plus CD-DVD rom drive; installation is a somewhat intensive process; the actual data sets may not be directly examined (as some other similar programs allow); search function looks only for the object name (or partial text), not other characteristics like type or constellation. We have purchased, tried carefully, and decided that we prefer other software for more advanced observers. But many other satisfied users love it!

TheSky: one of the most comprehensive series of products for controlling a telescope and even an observatory! This is a classic star chart program, dating back many years: an enormous commercial success. Benefits: very elaborate customizing options; adaptability to almost any conceivable computerized telescope or mount; versions including extremely advanced functions; large databases; efficient functionality. It may be adapted, with some effort, to use the excellent ASCOM telescope control drivers. Shortcomings: some versions of the program have database limitations (non-standard syntax; some discrepancies between catalogues; a certain learning curve required to understand and adapt to peculiarities of cataloging.) We use this program.

MegaStar: For many years this software has been considered "state of the art" for the advanced observers who own large telescopes that can see just about everything plotted in the Uranometria atlas! It is an extremely intellectually satisfying product, with many customizing options and capabilities for displaying tens of thousands of sky object photographs, with integration of star chart plots with actual images of galaxies, nebulae, and so forth. It is unique in employing a gargantuan database of galaxies, painstakingly corrected by amateur astronomer Larry Mitchell. Benefits: reasonable price considering depth of data and functionality; unsurpassed object accuracy and plotting precision; comprehension. Shortcomings: telescope control options are not as advanced and functional as other programs (ASCOM is not supported, for example), and development is limited since -- like Project Pluto (below) -- MegaStar is largely a "one man" operation.

Project Pluto: Guide: the "data wonk's program", with just about every conceivable sky object catalogue. Benefits: low cost; very easy installation and no large demands on hardware; deep references and catalogues. Shortcomings: odd and quirky, unique interface that is somewhat non-intuitive; not very extensive telescope control options; rather unrealistic, slightly crude looking sky displays (an inheritance, one imagines, from its DOS origination.)

Planning Programs

We have tried a number of these alternatives to star charts, which enable the user to put together a spreadsheet for planning an observing session. The ones we purchased were, frankly, significantly flawed and unsatisfactory, and we've ceased to use them altogether, preferring the planner in our copy of Starry Night. Others seem attractive (most notably SkyTools by Greg Crinklaw, which has received excellent reviews, and is backed with fine web resources), but we might suggest that you try free ones first -- or demos -- and see if they are useful; we prefer star charts (printed or software) rather than laboriously creating lists of objects for observing, since we often change our mind about what we want to see, at night with our scope, due to sky conditions (such as light pollution in certain directions.)

An elegant list of almost every conceivable type of astronomy software may be found here: ASTRONOMY SOFTWARE by Dan Bruton.

Freeware for Windows™

Telescope Control: First and foremost, here is one of the finest programs available for controlling a computerized telescope, even measured against expensive commercial products: RTGUI, a FREE program with a rather strange title (meaning "real time graphical user interface") but with superb and intuitive functionality, backed by an enormous effort in development and debubbing by its author, Robert Schaeffer. The home page will explain the many optional catalogues that may be added, and the documentation is extremely thorough (though it does demand a certain level of computer expertise.) A Yahoo user group exists, and the author of the software is very responsive to suggestions or requests for assistance. RECOMMENDED!

Star Chart Software:

•  Of the various freeware planetarium/star chart programs available for Windows users, the one that I find to be the least flawed, most efficient, and easiest to use is Hallo Northern Sky (HNSKY) by Han Kleijn. Unlike others of its type, the program is usable immediately with a minimum of fussing, and relatively simple to download in practical form: just get the small or large "basic package" programs on his download page (either 4 or 40 MBytes) and after the simple installation process you're ready to go after entering your geographical coordinates directly, or by clicking on the world map. The menus are readily comprehendible, and intuitive, and numerous customization options are available for experienced users with distinct preferences; but the default installation is quite satisfactory. The program was developed on an old, slow 100 MHz Pentium computer that is at present a very obsolete system, so anything you might have will run it quite efficiently (it's even relatively fast with the large Tycho star database turned on.) Telescope control is available by downloading the "ASCOM" package of drivers. Program documentation is thorough, and many files of information about deep sky objects in the large database of the Saguaro Astronomy Club will suffice for all but the most advanced "data wonk" users.

The current version 2.3.0L has fixed a small bug related to the case allowed for the search function string; Han is very responsive to user suggestions and corrected this problem after I brought it to his attention: thanks, Han! If you have an earlier version you should replace it with his newest build, posted in October 2007.

This program was a pleasant surprise, and while not as fancy as the best commercial products, is at nearly as good as anything of its type that was sold a decade ago. Even advanced observers with the fanciest starchart software may find occasional use for this program: the "lite" version makes an excellent, simple onscreen planisphere display if you merely want to check out constellations and what's up in the sky at a given hour; we use it in conjunction with our very fancy, expensive programs. RECOMMENDED!


HNSKY's basic constellation display

•  I am not very enthusiastic about this next program, but it is true that it does have many adherents and users: Cartes du Ciel, a free but very elaborate planetarium program, developed in numerous language versions, including English. There are many catalogues available though the documentation is spotty, inexplicit and even sometimes confusing, and demands user expertise. Some versions I've tried have bugs and odd behavior but one does not like to be too critical, considering the enormous work of producing this creation. The latest Version 3 beta (0.1.2) begins to achieve stability, functionality, and effectiveness (though it runs very slowly if you leave the 9000+ deep sky pictures on.) Still, the full-priced commercial star chart programs -- or "HNSKY" described above -- offer more real usability and reliability.

•  A free open source program with exquisite graphical beauty called Stellarium promises to offer exceptional realism, with the sky depicted as it is seen by naked eye, binoculars, or with small telescopes. The only catch: I don't even OWN a computer that will satisfactorily run it! Even on our 1.4 and 1.8 GHz machines, the operation was so slow that I could not tolerate it. On my slower machines, running at 1 GHz and under -- which all operate commercial star chart software like "TheSky" with crispness and rapid response -- Stellarium was so sluggish that I could not even finish the setup procedure: the screen cursor and dialogue boxes seem to be many seconds behind the user-input, being incredibly frustrating. So, our advice is not to bother unless you have a very fast, modern PC (and a state of the art Open-GL video card.)

Mini-Planner & Scope Controller: Celestron expert Mike Swanson's NexStar Observer List is an absolutely free planning program that may also be used to control a Celestron GOTO telescope. You may also use the program without a computerized scope, if you merely want to try an object list-generator and see if it will fit your needs. It can automatically link to "Cartes du Ciel" (as also can RTGUI) to plot charts of the sky region you wish to observe (though this function is buggy, due to the star chart program's interface limitations and anomalies.)

Moon Phase Calculator: The website of programmer Henrik Tingstrom has some useful software, including the freeware program Moonphase for northern or southern hemispheres. This would appear to be one of only three free Windows programs on the Net for moon rise/set calculations; almost everything else we've found is commercial or a shareware demo. The installation and setup of Henrik's program -- recently in fall 2007 updated to version 3.0 -- is incredibly simple and straightforward, and the screen display is cute! Unfortunately his calculations are a little bit off -- by a minute or two -- from the Naval Observatory sun/moon page, or the expensive commercial program Lunar Phase Pro (which will print charts; Moonphase won't.) But, Henrik has done a nice job -- if you are not demanding of absolutely perfect rise/set prediction accuracy, or MUST have printed charts. It's worth the 'free' price of a few moments to download it.

Alternative Moon calculator freeware programs that aren't quite as fancy are: the Texas A&M Astronomical Software Freeware Download Page's "Moon Rise & Set Calculator" (a small numerical panel which is very accurate but is not as easy to set up as it requires entering one's latitude and longitude in decimal format, or it crashes!); and NightCal Observing Calendar, which produces a printable chart of an entire month of data on Moon and Sun rise/times and phase display.

Whichever software you decide to use, after installing it be sure to refer to the US Naval Observatory sun/moon page in order to check the calibration of your program.

INTERMEDIATE/ADVANCED OBSERVERS: FILTERS & CLEANING OPTICS

In general, you will find that visual observers use two different kinds of filters: colored filters for improving the visibility of the planets; and nebular filters for diminishing light pollution from man-made street and city lights, and to enhance contrast of faint nebulae.

As explained above, human vision is different in bright daylight (when you can see colors) and dark night time (when you don't see much color but increase your sensitivity to very faint light.)

Day versus Night Color Vision Sensitivity:

In dim light, almost every 'extended' celestial object -- except bright stars, planets, and perhaps traces of color of the Moon's surface -- will look only gray to the eye. Though faint light color wavelengths are striking the eye's retina, it is sensitive at faint light levels only to differences of light and dark, not colors. So, nebular filters do not generally change the apparent color of very faint nebulae to the eye, when used in your telescope at night, though they will cut out the interfering streetlight colors scattered in the sky around you.

Below you will see the effect of the "light pollution rejection" (LPR) type of filter, which cuts out the yellowish light of streetlights, and also two of the narrower nebular filter types, which pass only certain colors of light from faint nebulae that one can see at night with an amateur telescope. By cutting out other "competing" light, the nebulae will show up better.

By using a nebular filter, you may sometimes be able to improve the contrast of faint nebulae. These devices are not always useful to the novice, or with the smallest types of telescopes that produce very dim images. But as you develop your skills and use improved equipment, they can be helpful tools.

(1) TYPES OF FILTERS & WHERE TO READ ABOUT THEM:

You may locate specific information in our 'Eyepiece' program help files about the various types of filters (light-pollution-reduction, nebular-line, and colored eyepiece filters,) Our web page version of a valuable article by Dr. Jack Marling on the development of his nebular filters, which is also found in the "Eyepiece" program documentation files, explains (on the level of intermediate- to- advanced users) how the filters work, and how Dr. Marling designed them. We have also prepared a general-audience level article as an overview of four types of nebular filters, with photographic test examples, which you may read here.

Our 'Eyepiece' program function that displays views of objects in light polluted and darker skies will show our "before and after" eyepiece simulations, demonstrating the effective the effective increase in viewing contrast with specific LPR/nebular filters.

Newcomers to the use of nebular filters who have not made any attempt to determine the proper magnification range for their use may sometimes select the wrong combination of object, filter, and magnification. Nothing bad will happen: it is simply that with too much magnification, the filter may reduce the visibility by over-enhancing the contrast: the view will be too dark to be useful. But, at too low a magnification, the filter may be hampered, and not work effectively. Some filters are inappropriate for the light radiated by a specific object. How do you know the optimal method of use for each filter?

• First, read Dr. Jack Marling's article on the development of his Lumicon light-pollution-reduction and nebular filters. .

• After reading Jack's article, you will understand what you SHOULD know about light pollution and natural skyglow, and how a properly- designed filter will reduce their damaging effects. You will also comprehend the difference between: (1) a broadband, general-purpose LPR filter to reduce light pollution, and (2) a narrowband 'line' filter, which transmits only the desired nebular lines of light frequencies that create the images of deep-sky objects you want to observe.

• Next, read our overview of four different eyepiece light pollution reduction and nebular filters for improving the contrast of deep-sky objects, including some interesting test photos and discussions of the latest opinions about using filters.

(2) THE GENERAL USE OF EYEPIECE FILTERS

Eyepiece filters for visual observing are manufactured in 3 sizes to fit the filter threads of standard telescope oculars:

0.965": Colored glass (planetary) filters; LPR Filter. This small eyepiece barrel size is now obsolete, so you will probably have difficulty obtaining filters for the 0.965" ocular threads: sorry!

1.25": ALL MODELS - Colored glass filters; the four standard nebular filters: the LPR type, the general hydrogen-line nebula design, the oxygen-line filter, and the hydrogen-beta line filter; plus specialized comet filters, and the eyepiece-adaptor version of the hydrogen-alpha solar prominence filter.

2.0": Colored filters; four standard nebular filters (as above), plus comet filters.

In addition, an extensive variety of photographic filters, ranging from 46 mm to 77 mm sizes, colored eyepiece and camera filters, plus many different types of adaptors to solve virtually any compatibility need, is available from a large number of reputable telescope dealers.

To see all the available colors, and how they improve specific details of the planets, visit The Use of Filters by Pulcherrima Productions. An extremely informative, advanced web page on using colored filters for planetary observing is this comprehensive article by Jeff Beish, a planetary observing expert.

To utilize your LPR or Nebular Filter:

(A) Check the nature of the object you wish to observe. Is it a nebula? If so, is it an EMISSION nebula, or a REFLECTION nebula?

Ron Wood's beautiful photograph of M20, the Trifid nebula: it consists of both
emission nebulosity (red, fainter green) and reflection nebulosity (blue) components.

Emission nebulae are helped by the LPR, general hydrogen-line, and oxygen-line filters; reflection nebulae are seen by the scattered bluish short wavelength light of bright stars, and are gemerally enhanced most by the broadband LPR filter: the resources specified in the paragraphs above will explain all the details that you will need to know in order to get started with your experimentation.

(B) Determine the size of your nebula or sky object in arcminutes. Consult EYEPIECE to see what the maximum field of view of your scope will be. Do you have an appropriate eyepiece that will show the object properly in the the field of view? Do not overmagnify nebular objects, or attempt to boost magnification until they fit the entire field of view, unless they are by nature very large in angular diameter. It is best to try to see faint nebulae or galaxies with some "space" around them in the eyepiece field in order to provide contrast. EYEPIECE's calculations will help answer these questions about proper field and magnification.

(C) Use EYEPIECE to set the proper eyepiece exit pupil within the range for the LPR or Nebular Filter you intend to use. EYEPIECE will calculate the magnification; it will even get an eyepiece from its database of 145 commercial oculars (though, admittedly, the last time the database was updated was 1996, and new ocular focal lengths are now available in some interspersed sizes.)

(D) An alternative way to accomplish the above steps is to use the "OBJECT" Function in EYEPIECE, which contains the complete Messier catalog, and many NGC & IC diffuse and planetary nebulae. Select an object from the database lists, and EYEPIECE will calculate its approximate surface brightness, take into consideration the darkness of the sky that you have defined, plus the light-gathering power of your telescope (as described in part of this online article about how the program functions.)

EYEPIECE will then automatically assign the object a VISIBILITY PREDICTION in your scope, select an eyepiece in a reasonable range of effectiveness for viewing the object, and add a nebular or LPR filter, if appropriate. Try the filter selected with an available eyepiece of the the closest focal-length chosen by the program; then work up and down in magnification until you have decided what looks best to your eyes! Remember that many amateur astronomers have different opinions about observing, specific objects, and techniques: so it is best to learn by your own experimentation to find what you like best. Consider our software, and articles, to be suggestions about where to start, if you aren't sure, but not "directions that you must follow". Amateur astronomy is an activity that should be enjoyed as a pursuit of learning and pleasure, and is usually not "hard science" practiced the way professionals do it.

CARE AND CLEANING OF OPTICS & EYEPIECES

Amateur astronomers might sometimes be surprised that professional observatory optics are often dusty, smeared, and soiled: the rule of thumb is often "clean only when ABSOLUTELY necessary!" That shiny, spanking new telescope mirror or ocular you have brought home from the dealer will begin to collect fine specks of dust immediately: upon the first use in the open air, all exposed optical surfaces will be coated by microscopic-to-visible grains of smoke and dust.

Yet, it is wise to remember that usually the particles are found on surfaces that are not precisely in the focal plane: thus, each tiny speck only serves to block a very small area, and to cause practically no real observable loss of light. Only when the surfaces are really dusty and dirty will the user notice a slight lack of contrast in the images, or a haze around bright stars, planets, or other objects. The best advice is to keep your optics properly covered while not observing. It is not necessary to make a fetish of cleaning them!

(A) CLEANING FIRST-SURFACE MIRRORS

If a first-surface mirror becomes excessively dirty or coated with dust particles -- sometimes requiring years of use before a sufficient buildup that justifies cleaning -- it may be carefully washed, presuming that the coating will not be damaged by any kind of solvent or soap to be applied (do NOT wash silvered optics without following the exact recommendations of the manufacturer!)

Please follow these basic steps ONLY with great caution! The authors of this program and website have used these procedures successfully, but we accept NO responsibility for their use by anyone else! You are on your own. If in doubt, do a search on the Internet for other advice, or talk to your telescope or optical dealer.

(1) Thoroughly wash out a sink with sufficient capacity to hold the mirror completely under water. Use a soft cloth, and be sure to wipe out any dirty particles, soap, cleanser, or any rough material that may scratch the mirror.

(3) Procure at least a gallon of DISTILLED water. Obtain a supply of liquid dishwashing detergent that is FREE of ANY perfume, oils, supplements, or additives. Have at the ready some 100% medical-grade cotton balls (dust free type if possible), some lint-free towels, a bottle of 99% to 100% isopropyl alcohol, and a source of moderately-hot air (such as a typical electric hair-dryer.)

(3) Carefully remove the mirror from the mounting assembly, retaining all mounting hardware, clips, spacers, or pads.

(4) Mix the hot and cold water taps until the water is JUST slightly warm to the touch. Adjust the water pressure for a GENTLE flow. Place a towel in the bottom of the sink under the faucet, and over the drain outlet. Put the mirror on top of the towel, under the water supply. Leave it there for several minutes, taking care NOT to let the water level run over the edge of the sink!

(5) Apply a small amount (perhaps a teaspoon or two) of detergent soap to the water in the sink. Make sure the water level is COMPLETELY covering the mirror surface. Turn off the water and let the mirror soak for a few minutes.

(6) Turn slightly warm, very gentle water flow again. Take one of the clean cotton balls, hold it by thumb and forefinger, and DRAG it with NO PRESSURE across the surface of the mirror, beginning at the edge. THROW IT AWAY; take another cotton ball, and repeat in parallel lines until the entire surface has been gently cleaned. BE SURE NOT TO PUT ANY PRESSURE on the mirror with the cotton balls: let gravity supply ALL the pressure you apply to the surface. Depending on the size of the mirror, you may use up a whole package of cotton! Furthermore, AT ALL TIMES keep the surface of the mirror COMPLETELY under water.

(7) Let out some of the water in the sink, while pouring distilled water on the surface of the mirror: keep it WET as much as possible! Then drizzle some of the 99-100% isopropyl alcohol onto the mirror surface, and rinse with more distilled water.

(8) Lift the mirror out of the water, and let the liquid drain. If the surface is clean, virtually all the water will run off without beading or leaving droplets. If a few little drops form, then hold the source of clean, WARM air flow (hair-dryer on LOW) a few inches from the mirror, and 'push' the droplets to the edge of the mirror with the air pressure; absorb them at the edge with a dry cotton ball.

(9) Place your mirror (surface-up!) on a clean, dry towel in a clean, non-drafty room, and let it dry for 15 - 20 minutes before attempting to reassemble your equipment. Your mirror surface now should be very clean and free from water spots if the original surface was smooth and unscratched, and if you followed the above directions with care.

(B) CLEANING GLASS TELESCOPE SURFACES

Objective lenses, or catadioptric scope corrector plates, may be cleaned with some of the same techniques, though their surfaces are more robust than those of delicate first-surface mirrors.

(1) Prepare a very clean, lint-free, soft cloth for use.

(2) Moisten the cloth with a few droplets of:

(a) a recommended commercial optical-cleaning solution;

(b) or a mixture of 50% distilled water and 50% high- grade acetone solvent.

(4) Take care NOT to use a sopping-wet cloth, or to apply so much liquid that it seeps around the glass surfaces (possibly contaminating interior surfaces, such as the insides of achromatic lens systems.)

(5) Carefully wipe the optics in smooth arcs from the center to the outside edges, applying VERY LITTLE PRESSURE. If the cloth picks up any grease or dirt, moisten and use a new, clean area before repeating.

(6) DO NOT disassemble any complex lens systems! Clean ONLY the outer surfaces exposed to the outside air (the outer lens of a telescope objective, or the outer surface of a corrector plate.)

(7) If you are attempting to clean specialized optical materials (fluorite lenses or modern ED-glass surfaces) be sure to follow the manufacturers' directions if they differ from the above suggestions.

Our further thoughts, based on a recent experiment cleaning our own Celestron SCT telescope's corrector plate, are found here.

(C) CLEANING EYEPIECES

During normal use, only the outer eye-lens of most oculars will be exposed to dusty air. The interior field lens may not need cleaning even after many years of use, if proper storage is practiced when not observing.

Follow the above procedures for cleaning the eye lens of your oculars, with these added suggestions:

(1) You may find it handy to use high-grade 100% cotton swabs in addition to the lint-free cloth described in Section (B) above. The outside edge of the eye lens often accumulates grease and dust particles that may be CAREFULLY removed with a moistened cotton swab: follow this procedure by cleaning with the cloth as described. Gently repeat with CLEAN moistened swabs and cloth surfaces until all the residue is removed.

(2) DO NOT apply cleaning fluids DIRECTLY to the glass surface of an eyepiece lens. Droplets of the liquid could -- because of capillary action -- flow around the edges and behind the lens, contaminating inside surfaces, and causing stains that will damage the optics. Apply your cleaning solvent ONLY with a moistened swab or cloth!

(3) In some types of oculars -- such as Kellners or certain brands of imported long-eye-relief types -- the outer surface of certain lenses may be in the focal plane. Thus, dust specks may appear sharply in focus, and will be particularly noticed during high-contrast lunar or planetary viewing. You may have to be more scrupulous with your cleaning of these types of oculars than with more 'forgiving' types, such as Plössls or orthos, where dust specks don't show up in sharp focus but merely -- if numerous -- reduce the brightness and clarity somewhat.

(D) CARE OF YOUR EYEPIECE FILTERS

Like any other piece of precision optical componentry, your eyepiece filters should be treated with care and kept as clean as possible. Because they screw onto the ends of eyepieces or camera lenses, such filters will be out of the precise focal plane of the optics. Any slight dust particles on the glass surface of these filters will not be seen in focus in your eyepiece view or photograph.

However, dust particles (as in the case of your telescope's objective lens or mirror) will slightly reduce light transmission. But it is VERY slight! For example, if you have a reflector scope with a secondary mirror, you are aware that the secondary is directly in front of the path of incoming light. A 1 or 2" secondary mirror does not block enough light to make your telescope useless; so, you can imagine how LITTLE light is blocked by a 1-2 micron dust speck!

If, however, you drop a filter into the dust, or have accidentally put a greasy fingerprint on its surface (we know YOU wouldn't do this: it was that clumsy guy at the star party who was responsible!) then the surface of your filter may be cleaned carefully.

Broadband LPR filters usually have a hard coating on one side, and an anti-reflective coating on the opposite side; premium narrow- band hydrogen and oxygen filters have an internal coating completely protected to the outside by glass, with anti-reflective coatings on both outer sides of the glass substrate. You may clean these filters with a clean, lint-free soft cloth and 99% isopropyl alcohol: be sure not to use 60% rubbing alcohol, which often contains lanolin and leaves a messy deposit. Put a drop or two on the cloth, and touch it very lightly to the surface of the filter, wiping in a circular motion from the center to the outside edge. Try to keep the glass free from smudges. Repeat the process gently until the surface is clean. Don't rub hard. However, remember that your eyepiece filter is MUCH more rugged than the first-surface mirror in your telescope!

Again, very tiny specks or surface deposits will have minimal effects. The author has been using his eyepiece filters for many years, and has not yet had to clean them!

Return filters to their plastic cases when not in use. Of course, do not directly touch the surfaces, or allow others who may not be familiar with proper care of optics to handle them without supervision.

Author Waldee views solar prominences with his Lumicon prominence filter system.

The special hydrogen-α solar prominence filter system (such as the one the author has owned -- shown above -- made by Lumicon) should be used ONLY in conformance with the instructions of the manufacturer, or the filter element could be overheated or bleached by too much sunlight and infrared radiation. Such a filter system should not be used in telescopes with a shorter focal ratio than about f/20 to f/30 (or as recommended) to prevent overheating the chemical components. Be sure always to use the 77-mm prefilter (which is absolutely necessary for safe visual use!) and to employ a Barlow lens ahead of the eyepiece filter assembly if needed to get the focal ratio high enough to achieve f/20 or above as specified by the manufacturer of the filter employed.

At f/30 or higher, the H-α filter assembly should be perfectly reliable. Since the filter is usually protected inside its assembly, except while attaching it to the scope, eyepiece, or camera adaptor, it is subject to less direct handling than an eyepiece filter. The author has similarly found it unnecessary to have to clean his H-α filter, since it is provided with routine care during use, and is always directly returned to its container before and after use.

Other makes, such as the Coronado system, use a different type of filter, called an "etalon", which should be stored carefully and not subjected to temperature extremes or dirt. Neutral-density solar filters are more hardy, but should be treated with just as much care: keep them clean and store them safely; but if they become dirty, follow each maker's cleaning instructions explicitly. For instance: the instructions for cleaning the Questar solar filter is found on this webpage, and is probably consistent with other makers: but check to be certain.

* * * * A FINAL REMINDER: * * * *
TAKE CARE to properly employ these special high-quality filters in the correct range of exit pupil for best results! If magnification (and exit pupil) are well outside the optimal range, you may see either no effect, or far too much filtering. Consult our EYEPIECE program for the exit pupil values for the filter to be employed. Then, do your own experimenting to see if you have other preferences.

THE VALUE AND APPLICATIONS OF "EYEPIECE 2.0"

Often an amateur telescope user gets in the habit of just "plunking in" an eyepiece. After a while, one may acquire a 'feeling' for the appropriate magnification range, but yet might not fully be exploiting the optics' and eyes' potentials.

The authors recommend that for best efficiency as a telescopic observer, the user of this program should be sure to print a set of eyepiece charts and to use them at the telescope. Then, the approximate visual field of view, exit pupil, magnification, star resolution, and viewing suggestions will be known for all of your eyepieces.

By referring to the eyepiece charts, it will be easier for the observer to estimate the apparent size of a galaxy or nebula in a given eyepiece's field of view than merely by "guess." Similarly, planetary and double- star observers will be aided by knowing what the optics are THEORETICALLY capable of providing. Deep-sky "nebula-chasers" will be able to see far fainter objects, and much more detail in them, when light-pollution or nebular filters are used at recommended exit pupils.

If you don't have it yet, you may download our free "Eyepiece" program here