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The question of which telescope is best for the beginner is asked a lot. Here are our thoughts on the best beginner telescope — it really depends on what is important to you! There are many factors, most of which can only be answered by you, to pick the best beginner telescope. Here are some general guidelines to help steer you in the right direction.

Price, portability, what you can see with your new telescope and features such as computerized and GoTo functionality are the common attributes for the beginner to consider.

Price is a very important factor, especially if you are a beginning enthusiast. You may not be sure that you or your family will stick with the hobby for the long run and want an entry-level price just to get you started. Of course, you may find that in no time at all you're ready to step-up to a larger, more feature-rich telescope. Or, your high level of interest in astronomy and desire to have a high-quality, more capable telescope right from the beginning may make the investment in a higher-priced telescope your best choice. No matter your budget - Orion will have the right telescope for you!

The design and size of the telescope has a lot to do with portability and what you can see.

Refractors are the telescope design that most beginning astronomers consider first. A refractor uses a lens that provides a clear, quality view and tends to be smaller and more portable. Refractors can be used for both astronomy and scenic viewing (with a correct-image diagonal). A small 60mm-70mm refractor is one of the most inexpensive investments you can make to get into the hobby. You will be able to see the Moon in great detail, the rings of Saturn, and a cloud belt or two around Jupiter. Smaller telescopes are very portable and inexpensive, but lack the aperture (size of optics/light-gathering capability) needed to see much outside of the solar system like faint nebulae and galaxies.

Some great refractor choices from Orion can be found in the Refractor Telescopes For Beginners category.

If you're looking for the next step up to a more capable, feature-rich refractor, you can explore these Intermediate Refractors.

Reflectors use a primary and secondary mirror to gather light from the universe to your eyes. Mirrors are more economical to manufacture and are available in larger sizes to gather more light and see beyond our solar system. Reflectors are used exclusively for astronomy and tend to be a larger, less portable telescope.

There are relatively inexpensive models that will allow you to enter the realm of deep-sky objects, as well as give excellent views of the planets. A 4.5" to 8" Dobsonian is perhaps the best "bang-for the buck" beginner choice.

With a scope like this, you can see things like the Orion nebula in nice detail, the oval structure in the Andromeda Galaxy, the Ring Nebula in Lyra, and many more deep sky objects. Best of all, these telescopes are big enough in aperture that they will probably last many years before being out-grown.

Of course you can spend more to include computerized capability found in the GoTo and IntelliScope Dobsonians.

Cassegrains make a great portable telescope using a combination of mirrors and lenses. They are very portable, can be used for scenic viewing during the daytime with a correct image diagonal, and are available in larger aperture with less weight to manage.

Here are some great, entry-level Cassegrains for Beginners.

If price isn't quite as much of issue and you want to invest more but still don't want something overwhelmingly large, consider these Intermediate Orion Cassegrains.

As you can see, there are many different types of scopes that can be a great first telescope - consider a few of the factors we've described here before you make your decision and you can't go wrong.

Or just send us an email at sales@telescope.com, contact us via live chat, or give us a call Toll-Free at 800-447-1001 and we'll help you find the right telescope!

Many people getting into nature study for the first time wonder whether they should start by purchasing a spotting scope or a binocular. Of course the answer to this depends on many things. Two of the most important factors concern the nature of the subjects to be observed and the distance between them and the observer.

In almost every instance in which the subject is near, or in situations in which only wide field views are desired, the binocular should be the first choice. They are convenient to use, offer a wider field of view, and, because of the ability to use both eyes, may yield as much as a 40% improvement in contrast.

Handheld binoculars, however, rarely come in magnifications higher than about 15 power. Thus for subjects which must be viewed at great distances, or on which greater magnifications are required, the spotting scope is the only logical choice.

What is a Spotting Scope?
Passenger planes, jet fighters, cargo planes and crop dusters all have one thing in common; they are all types of aircraft, each with a specific role to fill, and a specific name that aptly describes that role. Similarly, "spotting scopes" are in fact telescopes that have been specifically designed for daytime terrestrial viewing.

Considerably shorter and lighter than their astronomically dedicated cousins, spotting scopes with apertures between 50mm and 127mm (2 to 5 inches) are excellent for increasing our pleasure in any number of hobbies and research projects. They can also allow us to safely view (or photograph) targets that might otherwise place us in harms way. Suppose, for example, you wanted to observe hornets circling about their nest. A spotting scope set at 20-power would allow you to stand 50 feet from the nest and yet enjoy a view as if you were only 2 1/2 feet away-virtually close enough to touch it!

Kinds of Spotting Scopes
Spotting scopes come in a variety of configurations, typically: Schmidt-Cassegrains and Maksutov-Cassegrains, in which mirrors are used to fold the light back on itself making the instrument more portable and convenient to use, and the more common refracting type. In these instruments, light is gathered and brought to a focus by an "objective" lens.

When subjects are at great distances, or when high resolution-the ability to see fine detail-is required, spotting scopes with relatively large apertures are often employed. In order to make these instruments as portable as possible a "compound" system-such as the Schmidt or Maksutov described above-become the only practical option.

The majority of naturalists, however, find their needs met by using refracting spotting scopes of moderate aperture-typically 50mm to 102mm (2 to 4 inches)-and they are by far the most popular.

The Basic (Fixed Eyepiece) Spotting Scope
These spotting scopes represent the best value when thinking in terms of aperture vs. cost. This is because of the simplicity of their design and construction. They consist of an objective lens, a prism to offset the line of sight to a more convenient 45-degree angle and an eyepiece. Magnification is increased or decreased by using interchangeable eyepieces of various "powers." It is this changing of eyepieces that leads many naturalists to choose the more popular and sophisticated zooming spotting scope.

The Advanced (Zoom) Spotting Scope
For individuals whose requirements are restricted to a limited number of targets at similar distances, or who will be making observations from their house or backyard, the spotting scope described above will perform admirably.

Bird watchers and other naturalists, however, are incessantly on the go and lean toward telescopes that can provide a variety of magnifications without having to locate and fumble about with a collection of eyepieces. For most of them, the "zoom" spotting scope is the instrument of choice. In general, they cost more than fixed-eyepiece scopes of equal aperture and quality, but make up for it in the convenience they offer.

Performance
Once you have decided which type of telescope will best suit your needs, and considerations concerning styling, weight and cost have been addressed, it is time to turn your attention to performance. The most important things to think about when considering a telescope's performance involve: Aperture, Magnification and Anti-Reflective Coatings.

Aperture
Aperture is the measurement-usually stated in millimeters-of an instrument's main lens or mirror. Every square inch of an objective lenses surface gathers as much light as 9 eyes wide open. This means that even a 60mm spotting scope is capable to gathering more light at any instant in time than 41 eyes! This explains why many people new to using optical instruments show great surprise with the ability to see things very well in low-light situations, or in shadows, that would otherwise be invisible. This is not a magical power of some high-tech marvel, just a simple optical system exploiting the laws of physics.

But how much aperture do you need? Everything we see either gives off or reflects a finite amount of light. Thus, to observe faint objects, or objects in poorly lighted areas, the greater the aperture, the brighter the image will be at a given magnification. But then we must look at the practical limits of size, weight, and cost. Those wanting to watch a group of goats a mile up the side of a mountain should consider spotting scopes with an aperture of 80mm or more, while those who demand little more than the ability to provide a good view of birds at a backyard feeder, a 40mm to 50mm instrument would perform quite well. For the needs expressed by most bird watchers and naturalists, telescopes with apertures between 60mm and 80mm will be a good compromise between portability and light grasp.

Magnification
Few things in optics are understood less than magnification. Owing to the endless stream of articles and sales brochures extolling "high powered telescopes," the unwary consumer is often left to believe that magnification is the single most important feature to consider when planning the purchase of a spotting scope. This is simply not true; one should not use more magnification than is necessary to do the particular job for which it was selected. Why? Because when you increase magnification you:

1) decrease image brightness by spreading available light over a greater area

2) decrease the field of view; making objects harder to find and keep centered

3) introduce more image degrading vibrations

4) accentuate atmospheric disturbances

For years, the most popular spotting scopes have had magnifications ranging from 15 to 60 power, topping out at about 25% of the "theoretical" magnification for a good 60mm telescope of any type. However, pushing mathematical modeling aside and sticking to the practical limitations of the instrument, an observer will be assured of having nothing but good viewing experiences. Unfortunately, many observers fall into the "bigger is better" trap, and push the limits of their spotting scopes to the point that they are left with fuzzy, jittery images.

Optical Coatings
Good anti-reflection coatings are crucial to the optimal performance of any optical instrument-especially binoculars and spotting scopes. At the beginning of the Second World War, only about 50% of the light that was captured by a 7x50 binocular's objective lens managed to get to the observer's eyes. The rest was absorbed into the glass or scattered about in the system. With the development of anti-reflection coatings light transmission was increased to 85 percent. Today, magnesium fluoride coatings can increase light transmission to about 89 percent with multi-coated lenses transmitting up to an incredible 98% per surface!

A Word About Tripods
Most naturalists mount binoculars with magnifications above about 10 power on a tripod, and since spotting scopes have magnification ranges that usually start at 15 or more, it stands to reason that all spotting scopes will perform better if mounted on a good tripod.

Tripods come with a variety of features, and prices vary accordingly. Unlike spotting scopes, however, most good models remain the same for several years. Thus, wise shoppers should select a model with the quality and features necessary to make their purchase a lasting value.

Some Points to Consider

Rigidity:
Select a tripod specific to its application and the size and weight of the load it will be expected to carry, keeping in mind that rigidity is more a product of design than weight. Birders tend to be on the go and usually want a tripod that is lightweight-just large enough to carry a light duty binocular or spotting scope. Amateur astronomers, on the other hand, tend to use their tripods in only one or two locations in the course of an evening's viewing session and tend to use heavier equipment. Placing a rickety or poorly designed tripod under a $1,000 spotting scope is tantamount to hitching an expensive sports car to a team of goats-you could save on gasoline, but, overall, you would probably notice a few frustrating shortcomings in the decision to do so.

The Legs:
Photo tripods have legs with three sections that "telescope" in two places, allowing a tripod that might stand more than 5-feet tall while in use to be collapsed to just over 2-feet for storage or travel. Locking mechanisms may be of the clamp- or screw-type. If properly made, these styles will perform equally well. However, the clamp-type provides for much faster set-up and adjustment times.

The Head:
A tripod's "head" is the part onto which the spotting scope is attached. Older, or less expensive, tripods often have heads that are adjustable through the loosening and tightening of two bolts-for up and down and side to side motion. A refinement to this is seen on heads on which these bolts are operated by long handles that can be used not only for tensioning, but aiming the instrument as well.

The best tripods have "fluid" heads-"fluid" referring to the smoothness of motion and not a liquid component-which operate on a user-adjusted clutch system that can be easily adjusted to match the tension needed to support the weight of a given instrument.

The Shoe:
Some spotting scopes attach to tripods through the use of a 1/4-20 screw which passes through a metal plate on top of the tripod head and into a mounting bracket on the bottom of the scope. While this is a very efficient way to attach the tripod, it leaves much to be desired when speed is of the essence-as it usually is.

In many of the best tripods, the metal plate (or "Shoe") mentioned above is removable and may be left attached to the scope at all times. The scope may then be placed onto the head by snapping the shoe into the top of the tripod head, and removed with a "quick-release" latch or finger lever. This not only makes it possible to have several instruments ready for use at a moment's notice (additional shoes may be purchased separately), but lessens the chances of the scope being dropped while trying to attach it to the tripod.

Final Pre-Flight Instructions
1) Consider how you intend to use your new spotting scope. If it is just to be used around the house in daylight, a 50mm or 60mm instrument might be just the ticket. If you are an avid birder in search of getting a better look at those high-nesting raptors, you will want to consider an 80mm to 127mm telescope.

2) Decide which style will best suit your needs. A fixed-eyepiece will give you the largest aperture for the dollar; a zooming telescope will be the most convenient to use.

3) If you do not already own a good tripod, you will want to purchase one with your telescopes. The higher magnifications of a spotting scope will make holding it in your hands impractical.

4) Always use your spotting scope at realistic magnifications-15 to 60 power; slightly higher in instruments with aperture greater than 80 millimeters.

5) Spotting scopes may range in price from $100 to more than $2,000. Don't be fooled into thinking that your enjoyment must be directly proportional to its cost. It is true that in most cases quality comes with price. However, optical experts agree that-once a certain level of quality has been reached-It often takes a 100% increase in cost to acquire a 10% increase in performance.

6) Have fun!

The Moon
Even the smallest telescope will reveal breathtaking close-ups of the Moon’s rugged, battered surface. New features are highlighted every night along the terminator, where the light and dark portions of the lunar disk meet. Craters, smooth lava plains, and jagged mountains abound, providing endless fascination.

Planets
Venus, Mars, Saturn, and Jupiter make great subjects for study with a telescope. They’re very small, even at high magnification, but are bright enough to see even from light-drenched city skies. Any size telescope can show Mars’ pale red disk (and often a polar ice cap), Saturn’s pale yellow orb and picturesque rings, and Jupiter and its bright moons. In good seeing conditions you’ll see Jupiter’s colorful cloud bands and its Great Red Spot.

Star Clusters
No telescope shows stars as more than tiny but colorful pinpoints. Double stars, like the famous blue-gold pair Albireo, are a popular target. There are also numerous star clusters of different sizes and brightness ... the jewels of the sky. It’s fun to hunt them down using a star map and see how many stars you can resolve.

Nebulas
Like snowflakes, no two of these ghostly clouds of gas and dust look alike. All are faint and in a telescope will appear mostly gray or greenish in color. But their shapes and structure are revealed with patient observing. Dark-sky observing sites will let you see much more.

Galaxies
Incredibly distant and challenging faint subjects, dozens of galaxies are visible in backyard telescopes of modest size, hundreds or thousands in bigger models. In dark skies with a 6" scope, you can discern hints of structure in the brightest galaxies. The more time you spend observing them, the better trained your eye will become at seeing faint details.

Pictures vs. Viewing
Human eyes are not sensitive enough to detect colors in faint light. Long-exposure photos of nebulas and galaxies show their true colors. It’s impossible for a photo to depict the real-time, low-light image you will see. Fortunately, the eye is often better at revealing glimpses of detail on the planets than the typical photo can catch.

Every beginning astronomer has to grapple with the topsy-turvy topic of image orientation in the telescope. Depending on the type of telescope and whether or not it is used in combination with a star diagonal, the image you see may be either upside-down, backwards, rotated, or normally oriented.

For most astronomical observing, it makes little difference if an object is seen upside-down or at an otherwise odd angle (after all, there’s no "right side up" in space!). However, for terrestrial viewing you certainly don’t want to see everthing upside-down. And when stargazing, it’s hard to compare what you’re seeing to your star chart if the image is inverted or flopped. Let’s sort out the different image orientations seen through different types of telescopes, and see how diagonals figure in the equation.

Refractor and Cassegrain telescopes, when used without a diagonal (which isn’t usually the case), produce an inverted (upside-down) image. The view in Newtonian reflectors is also inverted, or rotated at an angle depending on the eyepiece angle with respect to vertical. Straight-through finder scopes also invert the field of view. If you’re using a star chart, all you have to do is turn it upside down to match the view through the eyepiece.

Refractor or Cassegrain telescopes used in combination with a standard 90 degree "star diagonal" will provide a right-side-up, but backwards (mirror-reversed), image. Using a star chart is difficult; you have to read it from the back, or do the mental gymnastics to flip the image in the eyepiece left to right to match the chart.

Fortunately, there are special "erect-image" or "correct-image" prism diagonals available that solve the problem, providing a correctly oriented view. Porro prisms (classical erecting prisms) provide correct images while allowing viewing straight through the scope. They do not work with Newtonian reflectors, however.

The Dobsonian is a simple, low-cost telescope design popularized by San Francisco amateur astronomer John Dobson in the 1970s. It consists of a Newtonian tube assembly riding on a simple, wooden altazimuth base. A large primary mirror at the bottom of the tube collects light and concentrates it onto a small secondary mirror, which diverts the light cone out the side of the tube and into the eyepiece.

Their affordability and simplicity of operation make Dobsonians a great first telescope for entry into the hobby of amateur astronomy, especially those in the 6" to 8" aperture range. Larger Dobs, though bulkier to transport, are highly popular among experienced observers, thanks to their tremendous light-gathering prowess and, again, their affordability compared to refractors or catadioptric telescopes. Even relative to similar-aperture Newtonians on equatorial mounts, Dobsonians are delightfully economical.

A Hands-On Telescope
A Dobsonian is a telescope you can push around-literally. You point it by simply nudging the tube up or down, and left or right, with your hand. Side trunnions on the tube rotate on low-friction plastic bearings, allowing it to move up and down (altitude). The boxy base rotates horizontally (azimuth) around a center pivot. The motion on both axes is "buttery smooth," letting you guide the scope with just the lightest touch from one part of the sky to another. You don’t need to loosen and retighten clamps when targeting objects, as you must with other mounts.

Working with Gravity
The Dobsonian mount has one big advantage over other mount designs-it doesn’t try to fight gravity. The center of gravity lies directly over the center of rotation in both directions, so no matter where the telescope is pointed, weight is evenly distributed through the mount to the ground. This unique characteristic results in a dramatic reduction in vibration and oscillation, the inevitable downfall of many telescope mounts. Whereas in many telescopes the image seems to bounce around forever after the scope has been touched, this is not the case with well made Dobsonians.

Telescopes come in many different shapes and sizes. In recent years, "short tube," or "rich-field," reflectors and refractors have become popular. Their short-focal-length optics fit in stubbier tubes, making them lighter and more portable than "long-tube" scopes. (Rich-field telescopes have low f-ratios — focal length divided by aperture — typically f/5 or lower.) The physical differences are obvious, but how do short-and long-focal-length scopes differ in performance?

Field of View
The main distinguishing characteristic is the field of view. The shorter a scope’s focal length, the wider its field of view (for a given eyepiece). For many of the deep-sky treasures we so enjoy looking at — diffuse nebulas, open clusters, and big galaxies — a wide field is desirable to frame the whole object in surrounding starfield. Long focal lengths show a narrower patch of sky, which is ideal for viewing small objects like planets and lunar surface details.

Example: the Orion AstroView 120 (f.l. 1000mm, f/8.3) used with a 25mm eyepiece shows a 1.25° field of view (2.5 full Moon widths), while the AstroView 120ST (f.l. 600mm, f/5) boasts a 2.1° field (more than 4 Moon widths) with the same eyepiece. A wide viewing area also makes it easier to find objects, since you’re seeing more of the sky at once.

Image Quality Short-focal-length optics introduce certain optical aberrations. Short refractors have more visible chromatic aberration than long refractors. You’re likely to see purple or orange halos around bright planets and the lunar limb. With short reflectors, "coma" comes into play: stars appear like "commas" or "seagulls" near the edge of the eyepiece field. For most people, a little color fringing or coma is no big deal; for purists, they’re undesirable. These aberrations are less noticeable at low magnifications, which is why you shouldn’t push the power higher than about 100x in typical short-tube telescopes. Of course, high-end versions made with exotic glasses or with corrector lenses can handle higher power.

While a short-tube scope is likely to be more easily portable, choosing between a short-and long-tube telescope really boils down to this: If your main interest is in viewing or photographing the planets and Moon, go with long focal length. If deep-sky objects are what you’re after, the wide field of a short, rich-field telescope will do the job wonderfully — and more portably, to boot.

An eyepiece's apparent field of view is the angular diameter, expressed in degrees (°), of the circle of light that the eye sees. It is analogous to the screen of a television (not the picture seen through it). Eyepiece apparent fields range from narrow (25° - 30°) to extra-wide angle (80° or more). The true field (or real field) of view is the angle of sky seen through the eyepiece when it's attached to the telescope. The true field can be approximated using the formula:

True Field = Apparent Field ÷ Magnification

For example, suppose you have an 8" Schmidt-Cassegrain telescope with a 2000mm focal length, and a 20mm eyepiece with a 50° apparent field. The magnification would be 2000mm ÷ 20mm = 100x. The true field would be 50 ÷ 100, or 0.5° - about the same apparent diameter as the full Moon.

You might never guess it from looking at the sky, but estimates indicate that between one-third and one-half of all stars belong to star systems called double stars or binary stars. Double stars come in many different combinations. Some consist of a faint star teamed with a bright star, while others comprise two equal-magnitude suns. Still others have three or more members, and are called multiple stars. Then, there are optical double stars, two stars that only appear closely set from our vantage point. In reality, these celestial imposters are not physically linked, and in fact are nowhere near each other in space.

For amateur astronomers, binary stars offer both charm and challenge. Many pairs display beautiful color and/or magnitude contrasts, while others are so close together that "splitting" them becomes a good visual test of one’s optics and of the night’s seeing conditions.

In a double star system, the brighter star is labeled the primary or "A" star, while the fainter member is called the companion or "B" star. If the system has other members, they are labeled alphabetically C, D, and so on. Their apparent separations are usually expressed in arc-seconds, abbreviated ". (An arc-second is a small fraction of an angular degree. There are 60 arc-minutes in one degree and 60 arc-seconds in one arc-minute.) Seven-power binoculars will resolve, or separate, double stars separated by approximately 30". A 60mm refractor can split equal-magnitude doubles separated by 2" at high power. A high-quality 6-inch telescope can resolve binaries less than 1" apart, given nearly perfect seeing conditions (i.e., a very steady atmosphere at the time of observation).

Check Out These Pretty Pairs
Some of the prettiest doubles in the sky are made up of two color-contrasting suns, where both shine like glittering jewels against a velvety backdrop. One of the most dazzling binary systems is Albireo in the summer constellation Cygnus. Here, a golden primary star radiates in sharp contrast to its fainter companion, which is blue. Another gorgeous double is Eta Cassiopeiae in the constellation Cassiopeia. It features yellow and red members separated by about 13 arc-seconds.

The table below lists some of the sky’s most interesting stellar couples. You’ll need to refer to a star atlas to find them.

Notes:
"Mag" is the visual magnitudes of the A and B stars, respectively.
"Sep" is the separation of the component stars, usually expressed in arc-seconds (").

Resolution and the Dawes Limit
While all of the doubles in the listing here should be resolvable through nearly all amateur telescopes, others challenge both our eyes and our telescopes to be seen. Just how close will your telescope be able to resolve a double star? In the 19th century, a British astronomer named William Dawes experimented to find how close he could resolve a pair of 6th-magnitude stars with different apertures. This value, called Dawes’ Limit, can be estimated by dividing 4.54 by the aperture of a telescope in inches. In other words, a 6-inch telescope should be able to resolve a pair of 6th-magnitude stars separated by 0.8 arc-seconds, while an 8-inch telescope can resolve stars to 0.6 arc-seconds.

But this is not set in stone. While Dawes’ Limit is a good guide for testing a telescope’s optical quality, resolving power can be greatly affected by a number of things. Above all, seeing conditions play a tremendous role. "Seeing" is a measure of how steady the Earth’s atmosphere appears. A good way to judge seeing conditions is to check the stars. If they appear to be twinkling, which is caused by a turbulent atmosphere, then Dawes’ Limit will never be reached. Frequently, the steadiest nights appear slightly hazy, when our atmosphere is more tranquil and seeing is enhanced.

Easy on the Power
Equally important is the optical quality of a telescope’s optics as well as those of the eyepiece and the observer’s eye. Refractors are often favored for splitting tight binaries, but reflectors and catadioptric telescopes can be equally adept provided their optics are precisely collimated. The secret to success is not to overpower the telescope. Use moderate powers for the best results, as high magnification will also amplify atmospheric turbulence and optical faults.

To test Dawes’ Limit for yourself, choose a binary star that has two equally bright components, both as close to 6th magnitude as possible. A large disparity in star brightness will render the test null and void. Beside steady seeing, be sure to use a moderate-power eyepiece, wait for the telescope’s optics to cool to the ambient outdoor temperature, and move away from any buildings and other objects that may be radiating the heat of the day. Dawes’ Limit will never be reached if test conditions aren’t just so, but under the right circumstances, some observers can actually exceed it.

Observing double stars is a great project for anyone who is looking for an enjoyable and varied observing program as well as an enjoyable way of testing the acuity of both your telescope and yourself. Dozens, even hundreds of targets are waiting for you in tonight’s sky. Perhaps best of all, double stars can be studied from anywhere any clear night of the year. Unlike other, diffuse deep-sky objects that are badly hampered by light pollution, double stars look striking even from urban or suburban skies, even at Full Moon.

Before the invention of the telescope, our ancestors marveled at the permanent nature of the stars at night. Planets, the Sun, and Moon moved, and comets occasionally appeared in the sky, then faded, but the stars remained constant and fixed to the celestial sphere. They were considered a source of great stability in an otherwise unstable world. At least, most were. There were exceptions.

Even in ancient times, some rogue stars were known to misbehave and were regarded with awe and fear. One such star was located in the constellation Cetus, the Whale. At times, it could be seen easily with the unaided eye, while at others, it was only dimly visible, if at all. Early skywatchers named this star Mira, which means "wonderful." Then, there was the case of the Demon star, Algol, marking the evil eye of Medusa's decapitated head in the constellation Perseus (hey, nobody said constellation mythology was pretty!). Algol winked at stargazers, varying from dim to bright over the course of about three days. What could be causing these amazing sights?

Once the telescope was turned to the heavens, astronomers began to discover more stars that changed in brightness like Algol and Mira. Today, thousands of these so-called variable stars are known and cataloged. Some fluctuate in brightness by only a few tenths of a magnitude, while others may vary by five or ten full magnitudes, or even more!

For amateur astronomers, observing variable stars can be an interesting and challenging pursuit, a different twist on typical stargazing. Before we get into the how-to of observing them, let's review the different kinds of variable stars.

Pulsating, Erupting, Eclipsing — They Vary
Variable stars like Mira are classified as pulsating variables. Known to be old, red giant stars, they actually expand and contract in diameter like a beating heart. Their rhythmic pulsations usually take weeks or months to complete a cycle.

A second class of variable stars suddenly and unpredictably change in brightness in just a few days, hours, even minutes, and so, are called eruptive variables. One example of an eruptive variable star is a nova. Here, a white dwarf star lying close to a normal star abruptly increases in brightness by five or more magnitudes, only to fade slowly back to its original, pre-eruption brightness over the course of several weeks. Another example of an eruptive variable are called R Coronae Borealis stars. These peculiar suns actually drop in brightness due to the formation of clouds of "soot" in their atmospheres.

Algol represents a third class of variable stars called eclipsing binaries. In these cases, the stars themselves do not fluctuate in brightness, but instead, are alternately covered and uncovered by unseen, orbiting companions. When a companion passes in front of or behind the system's primary star, their combined brightness fades, only to return after the eclipse ends. By measuring the period and amplitude of the fluctuations, astronomers can tell how far the two stars are apart and how long the companion takes to orbit. In the case of Algol, the orbital period is 2 days 20 hours 49 minutes, with the two stars separated in space by about 10 million kilometers (about 6 million miles).

How Bright is That Variable?
It?s fun to estimate the apparent magnitude of variable stars. This is usually done by comparing their brightness with that of neighboring stars of known (and fixed) brightness. The American Association of Variable Star Observers (AAVSO) has a collection of special finder charts for variable stars, which give the magnitudes of surrounding stars. The variable may appear to be the same brightness as one of the reference stars, which makes estimating its magnitude easy. Or, if the variable is brighter than comparison star A, but dimmer than comparison star B, then the variable?s magnitude lies somewhere in between. If star A is magnitude 8.0 and star B is 8.8, then the variable star may be about magnitude 8.4. This is called interpolation.

See the "Z": Check Out this Big Dipper Variable
Here?s a variable star that has long been a favorite among variable star observers. Z Ursae Majoris is categorized as a red, pulsating star, fluctuating between magnitudes 6.5 and 9.4 over a period of 195 days. What makes Z such a favorite is its location inside the bowl of the Big Dipper, about 2.5 degrees to the west-northwest of Megrez, the star that joins the bowl to its handle. This northerly location also means that the star stays above the horizon year-round for many observers in the Northern Hemisphere.

You don?t need fancy equipment to make accurate estimates of the brightness of variable stars — just your eye! It's really not as hard as it might sound at first. Begin by locating the star right in the center of the chart below, labeled with a "Z."

Some of the stars on the chart are numbered, while others are not. Those numbers represent the magnitudes of those stars. The decimal point has been omitted, since it would be easy to confuse it for another star. The star labeled "72" is really magnitude 7.2, while the star marked "86" shines at magnitude 8.6, and so on. These fixed-brightness "comparison stars" can be used to estimate the brightness of the variable.

If it's clear tonight, bring a print of the chart outside and find Z through your telescope or binoculars (you won?t be able to see it with your naked eyes). Begin at Megrez, then shift slowly north and west, following the trail of stars to its position (see "Star-Hopping: How and Why" for more details about locating sky objects). Be sure to use a low-power eyepiece to show the widest field of view. Unless it happens to be near its minimum brightness, Z should be bright enough to be seen through most finder scopes and binoculars.

With Z in view, take a look around at the stars in the eyepiece and compare them with the stars on the chart. Rotate the chart around so that the stars' orientation matches the eyepiece view. Remember, if you are using a star diagonal in your telescope, the view will be flipped left-to-right, like a mirror.

Begin by locating the variable star through your binoculars or telescope. Any type of telescope can be used, but be sure to select just enough magnification to see the star. Low power is usually preferred, since higher powers have very restrictive fields of view. Take a look around and find some of the comparison stars. Look for one or two that appear a little brighter than the variable, and one or two that are a little dimmer, then estimate how much brighter or dimmer the variable is from the others. For instance, you may find that Z appears a little dimmer than the "80" and "83" stars, but brighter than the "86" and "87" stars. If so, the variable must be either magnitude 8.4 or 8.5. Narrow your view now and scan back and forth between Z and the "83" and "86" stars. Try to decide if the variable is a little closer to one of the other, and mark down your estimate.

By keeping track of your estimates over the course of weeks or months, you will be able to plot a "light curve," a plot of the stars changing brightness over time. Mark the passage of time in days along the "X" axis (horizontal) and brightness along the "Y" axis (vertical). Plot the points matching the intervals of days and your magnitude estimates, then connect the dots. You?ve created a light curve just as professional astronomers do when studying variable stars!

Interested in viewing more variable stars? Here is a short sampling of the sky's most interesting ones.

Notes:
Mag is the variable's range in brightness.
Per. is short for Period, the number of days it takes the variable to complete a full period, or cycle, in brightness

Amateur observations of variable stars are especially sought by professional astronomers worldwide. If you are interested in learning more about observing variable stars, or in obtaining a set of variable star charts, contact the American Association of Variable Star Observers at 25 Birch Street, Cambridge, Massachusetts 02178, or visit their Web site at http://www.aavso.org.

Despite the advent of photography and CCD imaging, many amateur astronomers today prefer to chronicle their observations by making eyepiece renderings. Sketching at the telescope, however, does more than create a personal observing record. It hones the observer’s perception skills.

Say you look at a star cluster for a few minutes. In that time you may note whether it is rich or sparse, contains predominately bright stars or dim or a mixture of both. Afterward, you would come away feeling as if you "saw" this cluster.

But let’s say you sketch it. Now you may notice that some of its brighter stars appear reddish; that the chains form a kind of pattern; that what you thought was a sparse cluster actually contains myriad faint members. Instead if five minutes, you may spend half an hour scrutinizing this object, after which you would come away feeling that you "observed" this cluster.

All you need to get started is a red astronomer’s flashlight, an inexpensive sketchpad, and a sharp pencil or two. Before making your sketch, circumscribe a circle—not too small—representing the field of view and note where the cardinal directions fall in the eyepiece. Don’t forget to write down the date and time of the sketch, the telescope and magnification used, and a brief description of seeing conditions.

The eye may not be able to accumulate light like a photograph, but it often can see finer detail. That faint, fuzzy thing you saw last night might not appear as faint or fuzzy once you try sketching it!

Dew forms on any surface that is sufficiently colder than the air temperature. The dew point varies with both temperature and humidity. Odd as it may seem, the temperature of an object exposed to the night sky rapidly becomes colder than the ambient air. This radiant cooling takes place when an object gives off more heat than it absorbs from the surrounding environment. If the temperature drops enough to reach the dew point, dew forms.

Dew is particularly troublesome on Schmidt-Cassegrain telescopes, with their exposed front corrector plate. Once dew forms, wiping it away does no good; it just keeps forming. To prevent dew, you must either slow down the radiant cooling (with a dew cap) or replace lost heat (with a heater), or both.

Dew Caps
A dew cap is a hollow tube that extends out in front of the objective lens (refractors) or corrector lens (Schmidt-Cassegrains). It shields the exposed optics from wide exposure to the cool ambient air, slowing heat loss. Reflector telescopes don’t need dew caps because the main mirror rests at the bottom of the tube, which acts as a dew shield. A dew cap works best if made from an insulating material. It will prolong viewing time and can prevent dew formation entirely.

Dew Heaters
A dew heater warms the telescope’s corrector plate to a temperature higher than the dew point. There are several different types:

Warm air blowers, such as home hair dryers, can rapidly warm up optics and evaporate dew. They work well for casual observing, but must be used repeatedly and can cause temporary image distortion.

Heated dew caps warm the air around the corrector, heating it by convection. This eliminates dew, but can cause "heat wave" optical effects, which distort the image.

Contact heaters are electric heating elements that directly warm the telescope tube or optical mounting cell, which conducts heat directly to the optics. They avoid heating the air or the dew cap, thereby minimizing heat waves and other undesirable thermal effects.

You've probably noticed that when you first go outside from indoors on a starry night, you can see relatively few stars. But then, as your eyes adjust to the darkness, many more stars come into view. This phenomenon is called dark adaptation, and it is crucial for visual astronomy, especially for observation of faint objects, such as galaxies and nebulas.

There are many ways you can improve and maximize your night vision. But first we must understand how night vision works.

Dark Adaptation: A Complex Process
Dark adaptation begins as soon as you enter a dark environment, and it happens in several steps:

1. The iris of your eye opens the pupil, the "black hole" in the center, to its maximum width, usually 5 to 7 millimeters. Though this is the most visible aspect of dark adaptation, it is only the first step.
2. Next, a pair of chemicals in the eye, rhodopsin and iodopsin, begin to take effect. These two chemicals are always present in the eye, but they break down in the presence of light, so when the eye is exposed to bright light these chemicals have no effect. But when in the dark the concentration of these chemicals begins to grow and the rod cells and cone cells in the retina become more and more light sensitive.
3. At first, most of the increase in night vision comes from the cones, which are densely concentrated in the center of the retina. They are highly sensitive to color and are important for distinguishing fine detail. After 7 minutes or so the cones have reached their maximum sensitivity, while the rods, which are insensitive to color but are more sensitive than cones to low levels of light, keep gaining in sensitivity for another 20-30 minutes.

At the end of a half-hour or so the eye has achieved almost all of its dark sensitivity, with a small increase continuing until about 1 hour or so.

The Rods Have It
When your eye is fully dark adapted, most of your night vision comes from the rod cells in the retina. But the rods are not color sensitive, which is why in the dark you can see only shades of gray. The bright colors you see in pictures of nebulas and galaxies are typically only visible in photographs (film being much more sensitive to colors than a dark-adapted eye).

Most people are aware that night vision is not in color, but few realize that you see less fine detail at night as well. This is because the rods are not as tightly packed as the cones, so they cannot distinguish detail nearly as well. To prove this to yourself you need only look at a tree about 50 feet away: In the daytime you can clearly make out the leaves in the tree; at night you can make out the outline of the tree, but not the individual leaves.

Ten Tips For Improving Your Night Vision
So now that you know how night vision works, here's how to maximize your ability to see in the dark.

1) Observe from a dark site. Any amount of light will reduce your dark adaptation, so get away from street lamps, porch lights, car headlights, and urban skyglow.

2) Avoid bright sunlight as much as possible during the day prior to an evening's observing session, especially later in the afternoon. Exposure to intense light can hamper your dark-adaptation for a long time! Wear sunglasses when you have to go outside.

3) If you are in a light-polluted location consider wearing dark glasses or special red night-vision goggles at all times except when looking through the eyepiece. It may seem odd to wear dark glasses at night (and certainly don't do that when you're driving), but it can be a real help.

4) When you need some light to see what you're doing, use a dim red flashlight, the dimmer the better. A red light with adjustable brightness is very handy because it allows you to dial down the brightness to the bare minimum required. (Red light works best because it is less efficient than white light at breaking down the iodopsin and rhodopsin that allow your eye to see in the dark.)

5) Your eyes adapt to darkness independent of one another, so if you have to look at something bright do so with one eye, saving the dark adaptation of your other eye.

6) In light-polluted areas, do whatever you can to block ambient light from your eyes. For instance, consider using a dark shroud over your head to block out distracting light when at the eyepiece. Cupping your hand around your eye and the eyepiece helps, too.

7) When you take a break during a night of observing, say to go inside to warm up or grab a bite to eat, put on a pair of red goggles. If you don't need to see what you're doing, cover your eyes with a dark cloth and relax. Even though your eyes may seem fully dark adapted, after a half hour with your eyes completely sealed from light you may find that you gain a bit more acuity.

8) Use averted vision. The rod receptors, which are most sensitive to dim light, are more highly concentrated around the periphery of the retina than in the center. This means that you can see faint objects better by looking slightly off to the side of them rather than straight at them. Try it.

9) Breathe deeply. Avoid the tendency to slow your breathing rate or hold your breath when concentrating intently on a dim object. Reduced oxygen diminishes your night vision. Many experienced astronomers use the trick of "oxygen loading" before observing a particularly faint object, to enhance their visual acuity. Breathe deeply for 15 to 30 seconds just before looking into the eyepiece, and continue doing so as you observe. Don't go overboard, though. If you start feeling dizzy, breathe normally!

10) Avoid drinking alcoholic beverages before or during an observing session. Alcohol is a depressant and will decrease your visual acuity. Wait until after you're finished to crack open that cold one!

In astronomy the name of the game is seeing as much as you can possibly see. For that reason it pays to take a few extra steps to achieve and maintain your maximum dark-adapted night vision, particularly because it is so easy to do.