Learning to use your first telescope

The internet is bursting at the seams with telescope reviews, which is why I try not to add to that. However, it is harder to find some comprehensive advice regarding what to do when you get that package in the mail, put it together, wait two weeks for the sky to clear (the "curse" of buying a new telescope), and are ready to start observing.

Learning the telescope

Of course you will be eager to start observing, but before you put your new telescope outside under the stars, make sure you read the instructions, whether included with the telescope or found online. Put it together properly and understand what each part does. If you don't, you might end up frustrated that you can't find anything or wondering why everything just looks like a blob.

DO NOT start tweaking collimation, if your telescope allows it, until you know what you are doing. I can't count how many times beginners go online saying they can't see things well in their telescope and because they've heard about collimation they immediately think that's the problem and hopelessly screw up the telescope's alignment. Most telescopes are reasonably well collimated out of the factory and won't be out of alignment so bad that it will even be noticeable to a beginner. They also tend to hold collimation extremely well, so while it's something you will need to learn to do eventually, it's not something I recommend a beginner start messing with. That's a rabbit hole you don't need to go down when you are starting out.

Tripod and/or mount

Steady views are good. Most inexpensive telescopes that beginners buy, except for Dobsonians, tend to be undermounted, giving shaky and frustrating views. That's why advanced amateurs, especially imagers, spend gobs of money on big heavy mounts and tripods. The tripod is the three legged stand that holds the mount, which holds the telescope optical tube assembly (OTA). The mount provides movement in two axes, either in altitude and azimuth or right ascension and declination. Either system allows you to point the telescope tube anywhere in the sky.

Hopefully your telescope's mount is reasonably sturdy. If not, it's not the end of the world. You simply wait a few seconds after touching it (moving the tube to an object, focusing, etc.) for the vibrations to die down. If it's windy and you have a shaky mount, try to get behind a car or the side of a building to minimize the effect. Or just wait until it's not so windy. 

Left: The Explore Scientific FirstLight 102mm refractor, with main parts labeled.

A far greater impediment to observing is if the mount is difficult to move smoothly. This is where Dobsonians shine. You simply push the tube where you want it to go. I recommend putting one hand up on the lip of the aperture and the other near the back of the tube. This gives you more precise control and leverage.

Right: A Dobsonian reflector, such as the Apertura AD8, is a simple design that maximizes aperture and stability per dollar spent.

For tripod-mounted scopes, a lower quality mount will really become an issue when you try to move the scope to center an object and track it manually. Some just aren't designed well or are cheaply manufactured, making these operations incredibly frustrating. This is why I like slow motion controls. These are semi-flexible cables with a knob on the end that you turn to allow you to move the scope in finer increments than by just pushing the tube around. 

Main optics

Telescopes work by collecting as much light as possible using a larger aperture than the pupil of your eye. Refractors do this using a set of lenses. Reflectors use a large parabolic-shaped mirror. Catadioptrics (Schmidt-Cassegrains, Maksutov-Cassegrains, for example) use a combination of lenses and mirrors to create a light path that folds back upon itself. The larger the aperture, the more light the telescope collects. 

By concentrating and focusing this larger amount of collected light into a spot roughly the size of your pupil, a telescope allows you to see dimmer objects and more detail in even bright objects like the Moon or Jupiter. You look through an eyepiece inserted into the telescope where the light comes to focus. The eyepiece contains multiple lenses to magnify the image. In short, the telescope collects and concentrates the light, the eyepiece magnifies it.

Redirecting the light path for comfortable viewing

If you have a refractor or catadioptric ("cat") telescope (like a Schmidt-Cassegrain or a Maksutov-Cassegrain), you will first insert a diagonal, usually containing a mirror tilted at 90 degrees, and insert the eyepiece into that. The diagonal ensures that you have a comfortable position for viewing high up in the sky. If your scope comes with a 90 and and 45 degree diagonal, use the 90 for astronomy and the 45 for terrestrial viewing.

Because the diagonal is usually held in by a couple of thumb screws, you can rotate it to position it more comfortably for viewing. This will change the orientation of the view in the eyepiece, like tilting your head, but you learn to know which way is which after a while. There's no law saying you have to have it set vertically and look straight down into the eyepiece.

A reflector has a diagonal of sorts, too, but it's built into the upper part of the telescope tube. It's called the secondary mirror, and like the mirror diagonal, it's a flat mirror that redirects the focused light path 90 degrees so you can view in a comfortable position, either on the left or right side of the front of the tube.

Generally, a refractor or catadioptric will mirror-reverse the view. A Newtonian reflector will simply rotate it 180 degrees. Understanding directions in your eyepiece will help you make sense out of what you are seeing compared to a chart or image.

Changing magnification

Eyepieces, what some people call "lenses" (or "oculars" for the more esoteric term), are how you change magnification, or power. Except for specific eyepieces with a rotating barrel that actually are zoom lenses, each eyepiece will give you a fixed power depending on its focal length and that of the telescope. You change magnification by changing eyepieces. 

The standard eyepiece barrel diameter is 1.25". However, many telescopes have 2" focusers, allowing for larger eyepieces with 2" barrel diameters. Most of these come with a 1.25" adapter so you can use both, or you can buy one.

Magnification (or power) = telescope focal length / eyepiece focal length. So a 750mm focal length telescope with a commonly included 25mm eyepiece will give you 30 power (30x)—magnifying 30 times what your unaided eye sees. Place the eyepiece in the focuser or diagonal, making sure it's seated all the way in, and use the thumbscrews to clamp it tightly so it won't fall out. It doesn't matter how it's rotated. 

It's best to remove an eyepiece before you move the telescope to prevent it from falling out if the thumbscrews aren't tight. Get in the habit of frequently checking the tightness of all thumbscrews for eyepieces, diagonals, and finderscopes. After 30+ years with no incident, I recently had an 8x50 finderscope fall from the upright tube of my 10-inch Dobsonian onto the cement floor of the garage. Surprisingly, no damage, but it does happen. (Most finderscopes have a tab on one side of the base of the bracket, however the ones I've seen are always toward the back, where they don't help to prevent the finderscope from sliding out on a reflector, as mine did. Makes more sense to me to have the tab in the front, but it's a refractor thing.)

Taking a seat

Although I stood the first dozen or so years when observing with a telescope, I highly recommend finding a good seat and sitting while you observe. You will be more comfortable, you will get a steadier view, and you won't tire so quickly.

The longer the tube of your telescope, the more variation there will be in the height of the eyepiece as you view objects around the sky. You can get by with a stool or chair for a shorter tube, and for telescopes that use a diagonal you can rotate it to make up some of the difference, but longer tubes such as larger Dobsonians will require an adjustable chair. 

You can decide later if you want to spend the money on a commercially available observing chair, such as the Starbound, Vestil, Catsperch, or build your own. Some people also buy and use drum thrones with varying degrees of success. 

I built my own Denver Observing Chair, a popular option, for my 10-inch Dobsonian but I often use a collapsible stool for my 6-inch tabletop Dobsonian and 102mm Maksutov-Cassegrain.

Right: My homemade Denver Observing Chair that has served me well for over 20 years.

Finding objects

Your telescope should have some sort of finderscope, either what amounts to a tiny refractor mounted on the main scope that magnifies the view or a red dot or red circle finder that projects a dot or circle on a tilted glass or plastic surface and makes it look like the dot is projected onto the sky with no magnification. In either case, it is absolutely critical that you align the finder with the telescope. The finder has a low power (in the case of a red dot, 1x) and wide field so it's easier to find objects than looking directly in the main telescope.

Before searching for anything, focus your finderscope if you have one. This is usually done by loosening a ring near the objective lens and screwing the lens housing in or out, then retightening the ring. Also put your lowest power/widest field eyepiece in the telescope's main focuser and focus on any random stars. Focusing tips are covered later in this article.

Above: Simulated view of the field for the Owl Nebula, M97, in an 8x50 straight-through finderscope on a Dobsonian telescope in a light polluted sky. The view will be rotated 180 degrees from the naked eye view, which matches the view in the eyepiece.

Left: Screenshot from Sky Safari Pro showing the 8x50 field of view, rotated to roughly match the finderscope view above. You can customize the field of view to match your own equipment, which helps to match what the chart is showing to what you are seeing in the finderscope and eyepiece. The small circle around the planetary nebula symbol is the eyepiece filed of view. You can see how much more difficult it is to find something in the eyepiece without first centering it in the finderscope.

Sometimes the labels and other clutter can obscure some of the stars, so be careful. Zoom the screen in and out to see what might be hidden.

Below: Simulated view of the same field for the Owl Nebula, M97, in a red dot finder, also in a light polluted sky. The brightest star in both views is Merak, or Beta Ursae Majoris, magnitude 2.3. The view is the same as your naked eye view, with fewer stars visible than in a magnifying finderscope. 

In neither finder will M97 be visible, so you need to aim based on the location in relation to the star patterns from a star chart and what you can see in the sky. Without the magnification of a finderscope, the red dot loses a lot of precision, so it's critical that you use the lowest power/widest field eyepiece that you have once you are pointed in the right general direction. 

Sometimes, especially if the object is very dim and you may not recognize it right away, it's better to start by pointing the red dot at the nearest bright star, Merak in this case, then switching to the eyepiece and starhopping your way to the object by comparing the star patterns in your eyepiece to those on the chart. This sounds simple, but it's often difficult to be sure exactly where you are pointing, and it's easy to get lost along the way. It still happens to me all the time. It takes practice and, even with experience, patience.

It's easiest to do the finder rough alignment in the daytime. Find a distant fixed object, like the top of a telephone pole. Put your lowest power eyepiece in (the one with the highest mm number) and center the object in the telescope. Then, without moving where the scope is pointing, look in the finder and use the little thumbscrews on the side of it to put the same object in the center or crosshairs. Do this a couple of times, even using a higher power eyepiece for more accuracy, until you are sure they match.

Each time you go out observing, check the finder alignment on a bright object like the Moon, Jupiter, or a bright star, something you'll be certain you are pointed at. First in the main telescope, then in the finder and adjust the finder as needed.  Then when you use the finder to locate an object, it will show up in the main telescope eyepiece. Depending on how accurate the alignment is and how well you positioned the object in the finder, you may need to look around in the main telescope eyepiece a little to find it. Use low power when searching. You can always switch to higher power later.

Some telescopes have a go-to computerized mount, which requires battery power and must be leveled and aligned prior to observing. These aren't as foolproof and simple as they sound, and they often don't work right. They will have tracking, though, which keeps an object more or less centered in the eyepiece. These usually come with a hand controller or are controlled via an app. 

Another computerized navigation system is a variation of a push-to configuration, where an app guides you with arrows to manually push the telescope to the location of an object. Again, this must be aligned or calibrated. The Celestron StarSense app is a good example. It takes pictures of the sky and matches them to an internal database. A freeware push-to app is AstroHopper, which requires frequent recalibration but otherwise is a good alternative to pure starhopping or expensive commercial push-to systems.

Focusing

The basic rule for focusing is to slowly turn the focusing knob, or the focuser itself in the case of the helical focuser found on many tabletop telescopes, until the object gets as small and sharp as it can be. If it does so, but then gets larger and fuzzier as you keep turning the knob, then you know where the point of focus was and that you have passed it. Just go back slowly and find it. You may have to tweak the focus in very small increments back and forth until you get the best focus possible for the seeing conditions. Usually you will have to let the scope vibrations settle after each tweak. This is normal unless you have an exceptionally sturdy mount. If your telescope has a dual-speed focuser, you can use the smaller knob for fine focus adjustment, much the same for focusing as slow motion controls on a mount are for centering and tracking objects with more precision.

Stars should look like points in low power. However, in high power, you may begin to see the "Airy disk," which is the tiny disk of light that the star is spread out into due to the optics in your telescope, its size dependent upon the aperture of your telescope. Dimmer stars will still look like points in high power, but the brighter ones should look like tiny disks surrounded by a thin circle or two, called diffraction rings. This is what you want in a well focused and collimated telescope.

Above: If you look closely, the Airy disks and diffraction rings of the two brightest stars are visible in this simulated high power telescope view. Too often Airy disk images are blown way up in scale so you don't know what you should be seeing.

What if things don't look sharp?

Assuming thin clouds aren't obstructing your view and your focus is the best it can be, then by far and away the likeliest culprit is atmospheric turbulence, or what astronomers call "poor seeing." This is what causes bright stars to "twinkle." The seeing changes based on your location, night to night, and even minute to minute. Some places in the world frequently have very good to excellent seeing, or steadiness. Examples in the United States include much of the western U.S., as well as Florida. The northern, eastern, and midwestern U.S. are often under the jet stream, meaning nights of very good or excellent seeing are rare. 

Below: Jupiter and its Galilean moons in good seeing (L) and bad seeing (R). (Jupiter images by TheWitscher via Flickr, CC By 2.0, modified to simulate seeing conditions in eyepiece.)

You'll get used to knowing what's good and bad seeing through experience. When Jupiter, Saturn, or the Moon look like they are sitting in the bottom of a clear flowing stream, you have very poor seeing. Stars will look like undulating blobs. The view will shimmer and boil as waves of thermals pass in the atmosphere. You may not be able to make out a bright star's sharp Airy disk or diffraction ring in high power. Every object will just be a moving mess. 

Don't give up just because the seeing isn't great. It's not uncommon to have very brief moments when the air steadies out despite bad seeing. It might only be a split second every few seconds, but you can see a lot in those short bursts of good seeing.

Extended objects like galaxies and nebulae are less obviously affected by seeing, so if you have a very clear night but poor seeing (a common combination), go for those types of objects. 

At the other extreme, excellent seeing means you see stars as steady points or Airy disks, bright planets seem to be much larger than you remember and show a lot more detail to an experienced eye. You can see tiny craterlets on the Moon, the shadows are sharply defined with no double-edges, and you see little or no shimmering.

Seeing is also affected by thermal currents within the tubes of some telescopes, mainly reflectors and catadioptrics. Refractors not so much, if at all. This is why you will see some Dobsonian owners with fans installed to blow air through the tube, or "cat" owners who wrap their tubes in Reflectix or other insulating material. It's all to make sure the scope design is not contributing to poor seeing. In the former case, they are trying to cool the mirror down to ambient temperature or remove thermal layers inside the tube. In the latter, they are trying to slow down and distribute the cooling so there are no big temperature differentials or plumes inside the tube to cause poor seeing. 

In most cases. setting a reflector or "cat" outside for an hour or so before observing will help, but it's not always possible, given your situation. Just be aware that it may take time for the scope to "settle."

What about collimation?

Rarely is it the case where collimation, the alignment of the telescope's main optics, is so bad that it spoils the view as much as bad seeing. There are tools you can use to check and adjust collimation, but you're better off leaving those alone until you can recognize what is bad seeing versus bad collimation. With bad collimation, you'll often see one side of an object always fuzzier than the other. Stars may look asymmetric, like little bumblebees. On nights of excellent seeing you will still have a "soft" view that you can't quite focus. But don't assume it's bad collimation until you've ruled out bad seeing, poorly made optics, or even the nature of the type of optics. 

For example, a "fast" reflector with a small focal ratio, for example f/5, will normally show "coma" at the outer edges of the field, an abberation that makes stars near the edge look like comets. Same with achromat refractors and "chromatic abberation," where you may see blue or yellow color fringing along the edges of bright objects at higher powers, an indication that the focus is going to be a bit soft. These abberations are inherent in the design. Because most everything in life is a compromise.

Learning the sky

Using a telescope is like driving a car. You can learn to drive it, but if you don't know where to go or how to get there it won't do you much good. Even if you have a go-to telescope, the equivalent of an autonomous-driving car, knowing what you want to see, when is a good time to see it, and knowing what to look for are important for enjoying your observing.

Many experienced amateurs recommend buying a book to start learning. That's fine if you are a book-learner, but with so much information available on the internet, with options to ask questions and interact with other people, I wonder if starter books aren't a little obsolete. With younger people especially, I don't think learning from a book is a very appealing process. I think it just depends on the individual.

I did start with some books, but most of my actual learning came from simply getting out and observing, and then reading about the objects I saw. Back then, the charts in the book were most important for me, but with charting apps that's changed. Unlike paper charts, apps are flexible, can be zoomed in and out and filtered and manipulated however you want. So many nights I wished my paper charts went deeper than what they showed. And don't get me started on trying to find the right chart late at night for the area I wanted to observe!

Start with things that are easy to find: the Moon, the bright planets, M42, the Orion Nebula (winter), or M8, the Lagoon Nebula (summer), and brighter star clusters. 

We measure the brightness of celestial objects primarily by "magnitude," with higher numbers meaning dimmer, and lower numbers, including negative numbers, meaning brighter. The magnitude scale is reverse logarithmic, therefore a difference of five magnitudes is 100 times brighter or dimmer and each difference of 1 magnitude is about 2.5 times brigher or dimmer. 

Venus varies from magnitude -3 to almost -5. The bright star Vega is a reference at magnitude 0.0. The limiting magnitude of the unaided eye (dimmest you can see) in a transparent, dark sky is around magnitude 6 or 7. A typical 3-inch (80mm) telescope can reveal stars to about magnitude 12. A 6-inch (150mm) to about 13.5 magnitude. An 8-inch (200mm) to about magnitude 14. This doesn't sound like much of a difference, but it makes a big difference in what you can see when so many stars and deep sky objects are at these threshold levels for seeing details, or just seeing them at all.

Extended objects like larger nebulas and some more diffuse galaxies will appear dimmer than their listed magnitudes might indicate, in which case we say they have "low surface brightness." This is one of the reasons a larger aperture that collects more light can show many deep sky objects better than smaller ones. 

Once you are familiar with using the telescope and have seen some of the brightest objects, observing the rest of the Messier Objects is a good next step. Some of them are more challenging than those in the much larger NGC catalog, but the rest are some of the biggest and brightest. Be realistic in what you try to observe, but once you gain experience, don't be afraid to try for something normally just out of reach if you have a great sky. That's part of the fun of observing!

Navigating the sky

Learn how to navigate with your telescope, depending on what assistive equipment it has. Regardless, learn how to starhop. This means comparing the patterns of the stars you see in your finder or eyepiece with those on a chart and moving the scope to the object you want to see. Unless your go-to or push-to system is really precise and functions flawlessly every time (ha!), you will still need to recognize star patterns and be able to hop to the object from where your navigation system takes you. Knowing how to starhop will also ensure you can continue observing even if your electronic system fails or runs out of power—not an uncommon occurrence.

Observing

Don't expect deep sky objects to look anything like the images you see online or in books. Your eyes, even with the help of a telescope, can't gather as much light or see most of the wavelengths represented in images. So most objects will be white or gray and look rather like dim fuzzy blobs or patches, if you can glimpse them at all. Star clusters on the other hand, at least the ones your telescope can resolve into individual stars, will look like sprinklings of beautiful points. 

Once you learn how to observe and spend 10 minutes or more viewing an object, very subtle detail will eventually start to reveal itself on clear and steady nights. Learn to appreciate what you are looking as much as how it looks.

Except when viewing the Moon or bright planets, let your eyes get accustomed to the dark, which takes about 20-30 minutes for full dark adaptation. Use a dim red light when you need light.

As you observe more, you will learn what different objects look like, what to expect, what to look for, and how to improve your observing skills. Astronomerica has articles on using averted vision, understanding distances and directions in the sky, observing the Moon, observing the brighter planets, and observing galaxies, to name a few. The internet has a huge amount of resources.

Modifying and tweaking

Even a high end telescope may require some modification and tweaking by the user, if only to customize it to your own satisfaction. Inexpensive telescopes will almost always require some modifications to get the most out of the equipment, so expect that and don't be afraid to experiment. 

Right: I added the right angle bracket and 6x30 finder to my 6-inch tabletop telescope. I also added the light-blocking craft foam, a hose clamp and extra long focuser thumbscrews to improve the helical focuser. These are all reversible mods.

However, don't start making changes until 1) you're sure you are going to keep the telescope, to avoid return or warranty issues, and 2) you've tried it as is and determined there is a modification that you can do yourself that will likely make it better. Mods for specific telescopes are abundantly available online, often offering multiple options to solve common problems. The safest mods are those that can be undone to return the scope to its original condition.

Don't rush to upgrade

Once you're comfortable with all of the above, then you can think about upgrading. Or not. You really don't need a lot of gear to see a lot. You mostly need clear dark skies, good seeing, time, patience, enthusiasm, and experience. You can't buy that. 

Unless you are missing a critical piece of gear or it just doesn't work, upgrading equipment should be the last thing on your list. You might find yourself buying a lot of stuff you don't need, won't use, or will have to rebuy once you determine what items you really want or need after observing for a while.

The important thing is to get out under the stars.

Observing with bad vision

I've worn glasses for about forty years, and my vision has been getting progressively worse, as it usually will. It has stabilized in recent years, but now without my glasses, everything is a blur. I started out with hyperopia (farsightedness) which was joined later in life by astigmatism (irregular curvature of the cornea or lens) so, close or far, it's now all blurry. About 15 or 20 years ago I decided to try contact lenses, and now my typical observing session requires I put them in before going out. I don't wear them regularly, only while observing.

(Image by JSB Co. via Unsplash.)

Vision correction

There are nearly as many degrees and kinds of bad vision as there are observers. Most bad vision can be corrected at least to the point where observing is possible, and the telescope focuser takes care of any basic refractive errors in your vision. That's my case. While I have +6.5 and +7.0 corrective lenses that also help correct for astigmatism, the correction is not perfect. Nevertheless, for me progressive lenses correct enough for me to get through life. I don't recommend trying to use progressive lenses at the eyepiece.

Contacts don't do quite as well for me but they work better at the eyepiece. Although I have toric lenses, the astigmatism is still pretty strong, and I've gotten used to the idea that my views of astronomical objects are not going to be ideal—one of the reasons I don't spend a fortune on eyepieces! I have what's called monovision contacts. My left side focuses at about three feet to infinity and my right side focuses around reading distance. It takes some getting used to after wearing glasses, but within half an hour or even less I'm fully functional. 

(Star images rendered from AladinLite.)

Glasses on

Some people just observe with their glasses on. This requires you to have eyepieces with long eye relief, such that you can have your glasses in between your face and the eyepiece lens and still see the whole field of view, or at least most of it. 

Eye relief is the distance in millimeters from the closest your eye can get to the lens to the furthest point you can pull it back and still see the entire apparent field of view (you can see out to the circular edge of the eyepiece field). For eyepieces with very short eye relief, usually in the smaller focal lengths, this may be the same distance, and your eye has to be almost touching the lens. This can force you to strain and your eyelashes will deposit oil on the lens. 

When using glasses, this point may be closer to the eyepiece than you can actually place your eye, and in that case you will never be able to see the full field of view. Eye relief that is too long may require you to move your head around to catch the sweet spot and can be equally frustrating as the view blacks out when you move your head slightly out of position. Eye relief is also dependent upon the shape of your eye socket and your glasses.

I have yet to find an eyepiece with enough eye relief that works with my prescription, and I have progressive lenses anyway, so I don't wear my glasses when looking through the telescope. I can, however, use various binoculars with long eye relief.

Observing without glasses. Notice how close the eye can get to the lens, making longer eye relief unnecessary to be able to see the full apparent field of view of the eyepiece, which in this case is 82 degrees, nice and wide. Contact lenses require no additional eye relief.

Observing with glasses on. Compare to previous image, noting the much greater distance from the top surface of the eyepiece to the observer's eye. Long eye relief when wearing glasses is critical to being able to see most or all of the eyepiece field of view. This Astro-Tech UWA 10mm eyepiece has only 10mm of eye relief. Not long enough for eyeglass wearers, who need a minimum of about 17-20 mm.

(Images by Astronomerica.)

According to Don Pensack's 2025 Eyepiece Buyer's Guide, eyepieces currently available range in eye relief from a mere 1 to 3 mm for the Harry Siebert Optics Planesphere series to a whopping 46 mm for the Masuyama 60mm 2-inch eyepiece. The caveat on any eye relief figure is that the numbers often only count the measurement from the glass surface not including additional inset or eyecup. So if anything, the effective eye relief may be shorter than the advertised eye relief. This thread from Cloudy Nights discusses some of the better eyepieces for eyeglass wearers. Scroll to post 14 to bypass some rather less useful posts.

Glasses on and off

Another way to cope is to use your glasses when reading a chart or looking up at the sky and then taking them off each time you put your eye up to the eyepiece. This may work especially if you have a relatively mild prescription and maybe only use glasses for reading. For us hardcore Magoos (link provided for younger folks who have no idea), this is fraught with danger. 

(Superman image by DC Comics)

Let me relate my experience in that regard. Before I switched to contacts, I thought I would just swap my glasses on and off when observing. While annoying, this did work to some extent. Until one night, when I placed my glasses atop the roof of my car. They slid off with the heavy dew, and here I was with no way to search for them. Oh, I had a red light, but everything was blurry. I was afraid to move, but I took one step in the direction I thought would be away from the glasses and, you guessed it, heard and felt a sickening crunch underfoot. I managed to drive home that night using an older pair of glasses I had kept as a backup, but that was it for me, and I got contacts shortly thereafter. 

If it works for you, go for it, but be careful. Sometimes I still do use this technique (with my backup glasses!) when I'm just out for a quick look in the backyard or I'm taking a quick look in my solar scope. I recommend velcroing a soft case to your scope or table so you can slip the glasses in there, rather than trusting to a pocket that could contain who knows what that could scratch your lenses or just laying them on a table. I've tried keeping them on eyeglass retainers around my neck but the constant bumping and scraping as I leaned over the telescope was annoying and made me worry about scratches.

No glasses

You might be lucky enough to still be able to read or look at the sky without your glasses and still see reasonably well. In that case, just put your glasses away and use your uncorrected eyes. I did this until the stars just started looking like fuzzy blobs and I was straining to read charts with a magnifier in the dim red light of my flashlight. A man's got to know his limitations, and I had reached mine.

Contact lenses

For me, contacts are really the best solution. With my monovision lenses I can read reasonably well up close, I can drive, I can see the stars reasonably well when I look up, I can see pretty well with any eyepiece, and I've gotten used to using one eye for each. Another benefit is at public star parties, where I can focus an object in the telescope and know that people with reasonably good vision will get a decent look. But a tweak of the focuser will work for most people with uncorrected vision issues, other than astigmatism. I usually encourage people to take off their glasses to observe and just refocus, as long as they don't have bad astigmatism.

There are a few downsides, though. Especially if you don't wear them often, contacts can be itchy, scratchy, and blur out sometimes, especially as your eyes get tired. I sometimes struggle to get them to stay in at first, although other times they just slide right onto my eyeballs and stick. I've had them get stuck under my eyelid when I rubbed my tired eye, and I've even put two in at once, thinking the first one didn't stick and had dropped on the floor. 

Or maybe you just don't like touching your eyeball? Ewwww! (Image by Moist.acuvuehk via Wikimedia, public domain)

I always take a second pair of contacts with me in case I get a tear in one, it just feels crappy, or I somehow lose one out of my eye. Also bring eyedrops to rewet them if they get too annoying. The lens solution bottle won't help unless you want half the bottle all over your neck and down your shirt. Trust me on that one.

Televue DIOPTRX

Televue makes a device they call DIOPTRX that can help with mild astigatism. It looks like a filter with a fold-down eyecup attached that you can thread onto a variety of Televue eyepieces. I've read some accounts that all say it works well. If your astigmatism is relatively mild, but bad enough that correction would make it worth the cost, and you have Televue eyepieces, you might want to check it out.

Eyepiece cheat codes: Angular distances in the sky

In a previous post, we looked at cosmic distances and how they are measured. In this post, we'll look at angular distances as objects appear in the sky, and how to apply this to your observing. For this we use a system of degrees, minutes, and seconds of arc.

There are many resources on the internet that describe this system, so I'll only cover the basics. What we're interested in as visual observers is being able to translate numbers given to us in an app, article, or data source to what we see in the sky, especially in the telescope.

Because there are 360 degrees in a circle, the sky as we see it is always half of that, or 180 degrees. We are standing on the other half, as if we are standing in the middle of a globe. The zenith is 90 degrees overhead, so if the altitude of Jupiter is 45 degrees for our location at a given time, it will be halfway up the sky and good for observing if it's clear with steady air (seeing). At 20 degrees, things are a bit low and murky, subject to poor seeing and probably horizon light glow. 

Left: If we are using an altitude-azimuth mount like a Dobsonian, a degree in altitude is the same no matter how high we point our scope because all the circles of altitude are the same size. Think of these as lines of longitude.

But only if the scope is horizontal and pointed at the horizon is a degree of azimuth the same distance as a degree of altitude, because it's the only full diameter horizontal circle. As we point the scope higher up in the sky, the circles of azimuth, similar to lines of latitude, get smaller as we approach the zenith, so the apparent distance in the sky for the same number of degrees of azimuth is shorter. The higher we point the tube of the telescope, the smaller the arc it describes as it swings in the same number of degrees of azimuth.

As a result, we use a standard angular measurement of apparent distance essentially equal to degrees, minutes, and seconds of arc equivalent to any altitude circle (like a meridian of longitude, or our azimuth circle at the horizon only—essentially both great circles), regardless of what direction we are moving in, and we call them degrees, arcminutes ('), and arcseconds ("). 

Practical application

Left: At the scale of the unaided eye and binoculars, we usually use degrees. 

An easy rough estimate can be done with your outstretched hand.  

1 degree is about the width of your pinky 

5 degrees is about the width of your three middle fingers 

10 degrees is about the width of your fist 

20 degrees is about the width of your outstretched hand. 

This can vary considerably depending on the size of your hands and length of your fingers, but it's close enough for rough estimates. You can check how your own hand measures up by looking up the distances between bright stars that fit these measurements using an app such as Sky Safari Pro, Stellarium, or Cartes du Ciel.

When looking in binoculars or a telescope, your best bet is to know the field of view (FOV), or diameter of the portion of sky that you can see in your particular instrument, measured in degrees for binoculars and widefield eyepieces, and in arcminutes in higher power eyepieces. This will be fixed in non-zoom binoculars and will change depending on what eyepiece you use in the telescope. This is called the "true field of view" (TFOV) (or "actual field of view" in Stellarium), as opposed to the "apparent field of view" (AFOV), which is the angle of  "wideness" of your view based on the optics you are using. 

Left: The circle represents the true field of view (TFOV) in typical wide angle 10x50 binoculars. This diameter represents about 6.5 degrees of angular distance in the sky. (Chart adapted from Cartes du Ciel).

Left: The circle represents a true field of view (TFOV) of 35 arc minutes, or a little over half a degree in the sky, that is viewable in the combination of my 10-inch GSO Dobsonian with a particular 13mm focal length eyepiece. The apparent field of view (AFOV) for this particular eyepiece is 57 degrees. (View of globular cluster M13 adapted from Stellarium)

Left: A simplified diagram showing the apparent field of view (AFOV), which is determined by the lens configuration of the eyepiece and the eyepiece field stop or opening usually at or near the bottom. This does not change if you put the eyepiece in a different telescope. Manufacturers and vendors will state the AFOV in the specifications for the eyepiece.

Some eyepieces have a narrow AFOV because of their design, and it's like looking down a tube, whereas others have a wide, sometimes very wide, field of view, described as like looking through a "porthole" or on a "spacewalk," where you can't see the interior edge of the eyepiece, the field stop, at all without peering into the eyepiece almost sideways.

To recap, the AFOV is the apparent angle of wideness that you experience, but the TFOV is the actual angular measurement of distance in the sky that you are able to see, and that is what we're more concerned with here. Knowing this makes it easier to compare what you are seeing in your binoculars or telescope to your chart or unaided eye view.

Calculating TFOV in the telescope

TFOV must be calculated for each combination of telescope and eyepiece. You can use a variety of methods to calculate TFOV, with varying degrees of accuracy:

The easy calculated method

This method gives you a rough estimate because it is dependent upon the manufacturer specs being exactly correct, which is not always the case.

AFOV (provided by manufacturer or vendor) / MAGNIFICATION = TFOV (in degrees; multiply this by 60 for arc minutes)

Example: 60 / 30 (*see below for this calculation) = 2 degrees or 120 arc minutes

The published AFOV is often not completely accurate but usually fairly close.

*Magnification is calculated as follows:

FOCAL LENGTH OF TELESCOPE (in mm) / FOCAL LENGTH OF EYEPIECE (in mm)

Example: 750 / 25 = 30x

Both of the focal lengths above are provided by the manufacturers or vendors and are usually marked in millimeters somewhere on the telescope near the focuser and on the barrel of the eyepiece. 

The more precise calculated method

This method relies upon the manufacturer or vendor to provide the field stop diameter. Unfortunately, aside from Televue eyepieces, these are not easy to find (check out Don Pensack's 2025 Eyepiece Buyer's Guide, which lists many, or it can be calculated or measured with calipers). If you have it, here is the formula:

EYEPIECE FIELD STOP DIAMETER / TELESCOPE FOCAL LENGTH x 57.3 = TFOV (in degrees;  multiply this by 60 for arc minutes)

Example (for the Celestron Xcel-LX 24mm eyepiece pictured above and a 750mm focal length telescope):

25 (provided by manufacturer) / 750 = .033 x 57.3 = 1.89 degrees or 113 arc minutes

The drift method

This one must be done in the field with the telescope - eyepiece combination for which you wish to find the TFOV. Rather than go into the details, David Knisely provided an excellent description in this post from the Cloudy Nights forum. He also provides descriptions of some of the other methods.

The app or chart method

This one is also accomplished in the field and is another rough estimate. Again, With the telescope - eyepiece combination for which you wish to find the TFOV, locate any two easily identifiable stars that just fit on the edges of a full diameter of the eyepiece field of view, and measure the distance between those stars in the app. This is inherently inaccurate because you have to eyeball it, but it will give you a number close enough for casual observing.

Using TFOV in starhopping

Fortunately, apps like Sky Safari Pro, Stellarium, and Cartes du Ciel let you specify the custom TFOVs for various combinations of telescopes and eyepieces. Once you've set those up, it's easy to starhop around by moving the background behind the TFOV indicator in the app and seeing how far you need to move from one object to another in the telescope. 

For example, "I need to move two-and-a-half fields of view in my 750mm 6-inch telescope using the Celestron Xcel-LX 24mm eyepiece (1.89 degree TFOV as calculated above) to get to M13 from Zeta Herculis." (Chart adapted from Cartes du Ciel)

Once you're comfortable with this, your navigation skills will improve immensely.

How to get the most out of an astronomy outreach event

One of the coolest things about amateur astronomy is that we have "star parties." These can be local or informal outreach events open to the public or big events held annually at dark sky sites requiring registration and fees, and attended by people from around the world.

Outreach events

(Above: The Northern Virginia Astronomy Club teams up with Sky Meadows State Park to hold a monthly "Astronomy for Everyone" event for the public where club members provide views of the night sky through their telescopes. That's my white 10-inch in the foreground!)

Many astronony clubs, mine included, have monthly outreach events where volunteers from the club bring our telescopes and show members of the public some of the best celestial objects in the sky. These can have a variety of names, and while not quite the same as the classic star party, they have many elements of one, and the line can be blurred. Generally these are free and open to the public without any prior registration, and having your own telescope or even a knowledge of the night sky is not required—just an interest in seeing interesting objects in the sky and hobnobbing with astro nerds. 

Outreach events are a great chance to dip your toes into astronomy without having to invest in anything other than the gas to drive there and an evening of your time.

Great for beginners

These events are also great for beginners to check out various types of telescopes before buying, and to see what kind of a views can be had with each type and size of telescope. Owners are usually glad to let you look through their telescopes (ask, if there isn't a waiting line) and answer questions about their telescope, being an amateur astronomer, and the objects you are viewing.

If you are the proud owner of a new telescope and need some help, you'll find lots of it at an outreach event. In most cases, members of the public are encouraged to bring their own telescopes. It's always a good idea to get there while there is still plenty of daylight to set up your telescope and see what others have set up. You can get to know some of the other participants and ask them if they can help with your telescope. Just don't expect to show up never having set up your telescope before, aligned it, looked through it, etc. and think someone has the time or inclination to spend their evening getting you started. You need to do as much as you can prior to the event, and if you're still having some issues, explain what they are and ask if someone can give you some pointers. 

Telescopes of many shapes and sizes

There are four basic types of telescope that you may see at an outreach event: 

Refractors: the "typical" telescope that sits on a tripod with the large lens pointed at the sky and a little 90 degree diagonal attachment at the other end containing the eyepiece through which you look. (Pictured: Explore Scientific FirstLight 102mm refractor)

Reflectors: usually consist of a solid metal tube on a tripod or boxlike "Dobsonian" mount with the eyepiece sticking perpendicularly out of the open skyward pointing end of the tube (hidden by the finderscope in this image), or in larger telescopes, a mirror box connected to an upper cage with truss tubes, often requiring a ladder to reach the eyepiece. (Pictured: Apertura AD8 8" Dobsonian)

Catadioptrics ("Cats"): These feature a light path that folds back on itself to create a longer focal length in a short tube. These look like shorter versions of refractors, with a short, squat tube mounted on a big tripod, and are usually motorized to "go to" objects in a database and track them as the Earth turns. (Pictured: Celestron NexStar 6SE computerized Schmidt-Cassegrain Telescope)

You will also increasingly see "smart" telescopes that you don't look through, but are imaging telescopes that build up the image of an object as you watch, usually either on a cell phone or a tablet. (Pictured: ZWO Seestar S30 smart telescope)

The "Big Dobs," (example at right) the second type of reflector described above, will often require a ladder to reach the eyepiece,  and will often have long lines for viewing. Why? Because the larger mirrors used (sometimes 20" or more in diameter and housed in the box at the base of the scope) gather more light and can resolve smaller details. They make it easier to see deep sky objects—star clusters, nebulae, and galaxies—and to discern details that small scopes can't resolve.

But don't neglect the smaller telescopes. Often a high end refractor will show beautiful views of the Moon, brighter planets like Jupiter and Saturn, and double stars and star clusters. "Cats" have narrower fields of view but can also do very well on these objects as well as other deep sky wonders. Smaller reflectors are good general purpose scopes that can give great views of a wide variety of objects. 

Often the owner of the scope will be the biggest factor in determining how much you see and how enjoyable the experience is. Some people just really like to share this stuff, and I count myself among them. We try to give you interesting information about what you are looking at and tips on viewing it to enhance your experience and stimulate your curiosity.

Don't be afraid to bring your own telescope, even if it's very modest compared to others. Many people say that the best scope is the one you use most often. The beauty of small scopes is their portability.

Manage your visual expectations

Each night there are certain objects that will draw many of the telescopes. If Jupiter or Saturn are up, some scopes will certainly be trained on them. Showpiece objects for each season are also popular targets, as we like to show off the "flashy" stuff. The Moon is a great target, unfortunately it washes out the sky for all but the brightest objects, so events are usually planned when the Moon will be out of the way.

However, for deep sky objects, what you see visually in a telescope is nothing at all like the colorful Webb and Hubble space telescope images, or the many other professional or amateur images on the internet. Most people are just floored by seeing Saturn for the first time, but even a bright galaxy might seem like just a colorless faint fuzzy blob to someone seeing it for the first time. It can take years of experience to learn how to see fine detail in these objects.

Left: Messier 17, the Swan Nebula, imaged by the European Southern Observatory (ESO, CC by 2.0, via Flickr)

Left: Messier 17, the Swan Nebula, in the same orientation as it would appear in a typical backyard visual telescope. (Zager Family, CC by 2.0, via Flickr, modified to simulate visual view)

Getting the most from the visual experience

Ask the owner what it is you are looking at, how far away it is, how many stars it contains, does it have a black hole in the center, and appreciate it for what it is. That's the wonder of visual astronomy. Don't expect the view to knock your socks off every time, but appreciate that you're able to see something so huge and far away. Ask what you should be looking for and how to see it. Averted vision, looking away from a faint object slightly to see it better, is one of the big tricks of the trade in visual observing.

Don't touch any equipment unless the owner has told you it's all right. In most cases, the telescope will be aimed properly and you only need to put your eye up to the eyepiece (lens). Ask if you don't know where to put your eye.

For your own part, if you see what looks like bunch of round blobs, it's probably pretty far out of focus and you can ask the owner to help and show you how to focus. Pretty much any view should include many background stars. You want these to look like pinpoints, not blurry dots. When the blobs get smaller, you know you're headed in the right direction. Ask if you're not sure it's in focus.

Sometimes the "seeing," or the steadiness of the atmosphere is not very good, and nothing is completely sharp, but focusing will still get you the best view possible. 

Also, an object may drift out of view in an unmotorized telescope as the Earth turns, or someone may inadvertently bump the scope in the dark, so it may not even be in the field of view anymore. If in doubt, ask if you're looking at the right thing.

If you wear mascara, please don't on this particular night. The grease from mascara can rub off on the eyepiece lens and is very difficult to remove. Some eyepieces in use at outreach events cost many hundreds, and possibly over a thousand dollars. 

For those who wear glasses, some eyepieces have what is called long eye relief, which means you don't have to hold your eye as close to the lens as with some eyepieces to be able to see the entire field of view. In that case, you can leave your glasses on. But if you find much of the view is cut off, taking off your glasses and asking if you can refocus is a better plan, unless you have really bad astigmatism.

Red lights are standard when moving around at an astronomy event. The eye is not very sensitive to red wavelengths, so a red light will preserve night vision. That's why the bridge on a ship at night will use red lights, so the navigators can see out across the waves better. You can buy red flashlights, or put red film or tape across the front of a white light. We hand out rectangles of red film and rubber bands for people to put on their phones, because even a dim screen can still put out a lot of light. 

But a light is a light, so don't shine it in anyone's face or at a telescope when someone is observing or imaging. (Above: Sky Meadows outreach event at night. Image by Drew Prout)

Even in warmer months and climates, it can get much colder at night. Dress warmer than you think you'll need to, and you'll be comfortable. You can always take coats or jackets off. Bring bug spray if needed, but DO NOT spray it anywhere remotely near anyone's optics. Best to get a pump spray, spray on your hand when you're at your car, and then smear it on you.

Because we are at the mercy of nature, it's always possible that an event will be clouded or rained out. Keep an eye on the weather forecast, paying special attention to whether it is predicted to be clear or cloudy. Even in a partly cloudy sky, you may still be able to observe many objects. And we all know forecasts are not always right. Some events will happen rain or shine, with presentations and activities in the event of bad weather. Check the announcements to know what to expect so you don't make a trip out and find you're disappointed.

Astronomy events are great for kids

Kids love events where they can be out at night and see cool stuff. But they are notorious for wanting to just give a telescope a great big bear hug when they step up to look in one, so if you're bringing the little ones, explain in advance that they shouldn't touch the equipment. In most cases, it won't hurt the telescope, but it may knock it off the target, requiring the operator to recenter it. Putting fingers on the lens is a big no-no. (Credit: Aurore Simonnet, CC by 4.0, via WikiMedia)

Kids love to run around in the dark, but running around telescopes can be dangerous and can damage expensive equipment. Usually there is room for kids to run on the periphery of the star party, as long as they are away from the parking and driving lanes.

Many owners will have small step stools for younger kids to be able to reach the eyepiece comfortably. Ask if you don't see one. Don't try to hold your child up to the eyepiece. It's unlikely you will be able to hold them steady enough to get a decent view. Give them time to adjust to looking in the eyepiece. They might say they see the object, but kids often don't want to admit when they don't, so the owner might ask a few questions to make sure they are seeing it and it's in focus. 

What not to ask

Some questions or comments can be a bit troublesome for some astronomers, so here are a few to avoid:

• How much does this cost? Telescopes and equipment can cost for several hundred to many thousands of dollars. How expensive one is really doesn't matter and might be embarrassing to some owners unless you are into a conversation about buying a similar scope. They also don't want to advertise that they have expensive equipment that someone might be tempted to walk away with once they turn their backs. You can look up prices on the internet.
• Can you see the [flag, landers, footprints] on the Moon? These are way too small for any Earth-based or even Earth-orbiting telescope to see. It's not really a stupid question, but a little thought can probably get you the answer on your own. Check out the related links in my Becoming a Lunatic post if you're interested. Better question: Can you show me where Apollo 11 (or other lunar craft) landed?
• How did you get into Astrology? Astronomy is science. Astrology is mysticism. Two different disciplines entirely. (And it's "Scorpius," not "Scorpio"!) Substitute "Astronomy" for "Astrology," and you've got a great question there.
• Can I take a picture through the telescope with my cell phone? Holding up a cell phone to the eyepiece is not an easy thing to do, and often yields a pretty mediocre image. It will also take time away from others who want to view. There might be astronomers in attendance who have "smart" scopes where they can share digital images that you see on the screen- just ask.

The Classic Star Party

The strict definition usually used for a star party is a regularly occurring gathering of amateur astronomers who travel to a dark sky location to observe together over the course of several nights. These usually require registration, often well in advance, and include a fee for camping and participating. They will usually have guest speakers, workshops, vendors, and other organized activities during the day, with observing at night.

A few examples of the biggest star parties in the United States include Cherry Springs/Black Forest Star Party (Pennsylvania), Oregon Star Party, Texas Star Party, Okie-Tex Star Party, and in Canada (Ontario), Starfest. Go Astronomy has a good list of major star parties in the U.S., Canada, UK, Ireland, and Australia. 

Above: Starfest, held in Ayton, Ontario, is the largest star party in Canada.

Astronomy Magazine's article on star parties is a good start to get an idea of the attraction of these star parties.