Eyepiece Cheat Codes: Binocular astronomy

One of the common pieces of advice for amateur astronomers who are just starting out is to get binoculars. The reasons are that you can get a decent pair for less than a mediocre telescope, they are intuitive, compact, and easy to use, they help you learn the sky, and they will be useful no matter how experienced an observer you become. In addition, you can also use them for nature viewing, sports, and many other situations.

The main drawback to binoculars is that they don't magnify as much as telescopes and you can't change that magnification, at least for handheld binoculars. There are larger binoculars and  binocular telescopes that do both, but these tend to be very heavy and very expensive.

A second complaint is that it's difficult to take advantage of them fully for astronomy because holding them introduces shakiness and fatigue. Try keeping your hand on a telescope while you observe with it and you see how much it degrades the image.

But the beauty of binoculars are manifold. They allow you to use both of your eyes. They are eminently portable. They are uncomplicated: just point and focus. They have a wide field of view. They are inexpensive for the quality you get. They are widely available in many different size and magnification combinations. They are versatile. They are the ultimate "grab-n-go" astronomy gear.

Astroboy cartoon by Astronomerica.

Mounting binoculars

Besides learning how to hold it steady, you are going to get better views by mounting your binoculars in some way. For lower powered binoculars like 7x35 or 7x50 you can keep them pretty steady handheld, but once you get to around 10x50, even with a steady hold, you will still not get the good views that you would get if you mounted them. Also, any binoculars get tiring after holding them up with your arms for a few minutes.

For those reasons, many astronomers mount their binoculars. Most use a photo tripod or a monopod, but this limits the freedom of movement somewhat and certainly makes it uncomfortable to observe high in the sky, where the sky is usually darkest and most transparent. You can observe sitting down, but not in a reclining chair without difficulty. The best uses of a tripod are for objects lower in the sky, which is often the southern summer Milky Way for North American observers, and comets, which are often close to the Sun and visibly at their best shortly after sunset or before sunrise. I find a tripod very limiting overall.

Another option is the parallelogram mount. These are commercially available or you can build your own. I built one from plans in Astronomy magazine years ago, and while it worked okay, it was bulky and heavy. You have to adjust it if you move your chair to look at a different part of the sky. Commercial options are somewhat limited lately, and they are relatively expensive. Because I have to travel to observe in a darker sky, I don't have much room left after the Dobsonian telescope and other gear is loaded, so I don't want another big piece of gear and a tripod to mess with.

Some people don't bother with mounting and buy image stabilized binoculars instead. I've tried them and they're okay, but I get a bit dizzy using them. They are also quite expensive. You still have the fatigue of holding them up, and they are generally heavier than the same size non-stabilized binoculars.

My own preference is to build and use the compact, simple, and inexpensive Bino Body Mount (left), which you can use to observe anywhere in the sky (best up high) in a zero gravity chair for maximum flexibility and comfort. This lets you keep your elbows down by your side and transfers most of the weight to your shoulders directly, rather than through your eye sockets and arms. It preserves the freedom of motion of handheld binoculars and you can get views so steady that only your heartbeat is discernible.

What other equipment do I need?

Binoculars are the only essential equipment. There are many articles and videos about choosing binoculars. Generally, the higher the power the narrower the field of view. The larger the objective lens, the fainter and finer detail you will be able to see.

My recommendation is 7x50s if you are in the first half of your life and just beginning. They are easier to hold steady, have a wider field, lower power, big exit pupil (second number divided by the first, i.e., 50/7=7.1mm exit pupil) that young eyes can fully take advantage of. I recommend 10x50s, 15x70s, or 20x80s especially if you are older or interested in viewing more than starry vistas and want to locate individual objects like smaller star clusters, globular clusters, some nebulas, galaxies, and the like. These are the binoculars I recommend for my binocular audio guides "Space Walk Among the Stars."

But you'll really improve your observing and comfort with a reclining chair. A zero gravity chair is best because, unlike most other recliners, you don't need to manipulate the arms with both hands to change the reclining angle. Instead, you just transfer your weight between your feet and shoulders to change the angle, or altitude. The only drawback is the same as any chair: you have to get up and move it to view a different part of the sky. This leads some DIYers to build rotating platforms for their chairs. I recently built one, although I haven't got it quite right yet.

Left: Reader Mike (Telescope Guy) using his homemade rotating chair mount with his Bino Body Mount. Can't get much better than that!

For cold or cooler nights, besides dressing appropriately, a blanket laid on the chair will help insulate you from the cold air between the underside of your chair and the ground. I like to use a cheap moving blanket, but any blanket will do.

Unless you are just casually scanning the sky only, you will need some type of star chart, planisphere, or app. I use an app (Sky Safari Pro) with night vision turned on. Some will argue that this little bit of red light still disturbs your night vision, but I haven't found that to be the case unless I am observing in a super dark location, which doesn't happen very often. You'll have the same issue if you use a dim red flashlight and a paper chart, which to me is way too fussy for observing with binoculars. Even if  you don't have a specific observing list in mind, it's nice to be able to look up something you spotted to see what it is. I just attach my phone to the arm of my chair so I know where it is and it doesn't end up on the ground.

If you observe where dew is prevalent, you can add a pair of USB dew heaters made for camera lenses and power them with a phone power bank, which I recommend you carry in a pouch around your neck. If it's really dewy, and I've experienced this, or you are sweating from setting up, you can use a small battery operated pocket fan to clear the eyepiece lenses periodically.

What to look at

Well really, the sky's the limit. You can look at anything you want. But some things are too small and dim and are best left to telescopes.

The "Space Walk Among the Stars: Binocular Edition" audio guides are a great way to learn different areas of the sky and what objects are there. I suggest that you start with them.

Besides the Space Walks, here is a list of the types of objects you can view well in binoculars, with some examples for Northern Hemisphere observers. It's difficult to simulate the binocular view for each, other than adjusting the scale and dimming it down some from images, which I have done just to try to give you an idea of scale and brightness. But images just can't capture the sparkling beauty, color, and contrast with the sky that stars show visually. You'll find that these objects will appear much more entrancing in your binoculars, and you may end up staring at them longer than you expect. 

I've compiled an observing list of all the named objects below plus a few more, except comets and asteroids, in .skylist format for Sky Safari Plus and Pro. Download to your phone or tablet and import into Sky Safari Pro or Plus. Do this by emailing the .skylist file to yourself, open the email on your device, download it, then select the file, select "open with" and choose Sky Safari. You'll get an acknowledgment that it was imported. The list will show up as "Imported List" followed by the date and time. You can rename it in Sky Safari. 

1. Comets. I think brighter comets are best viewed in binoculars. The really good ones require a large field of view, larger than most telescopes, the tail shows best, and they're easiest to find quickly in binoculars. These tend to be brightest, with the longest tails, when they are closest to the  Sun. Therefore, low in the west in the evening and in the east in the morning is where you'll often be looking. The window for best viewing in these situations is often fairly short, so you want to be able to hop out before or after work or school and catch them.

Above: Comet C/2023 A3 (Tsuchinshan-ATLAS) by Kevin Gill, via Flickr, CC by 2.0.

2. Star fields. One of the truly amazing sights in amateur astronomy is getting out to a dark sky and just scanning the Milky Way with binoculars. Sometimes that's all I do, and I may not even set up my telescope. Binoculars (and the unaided eye in a dark sky) are the best instrument for these wide field vistas. A wide field refractor can be great, too, but being able to lie back, using two eyes, and the freedom to move around the sky easily with an orientation matching your unaided eye are huge advantages for binoculars. Check out M24, the Small Sagittarius Star Cloud, the area around Sadr in Cygnus, and the Belt of Orion for some standouts.

Above: Simulated binocular view of a star field in Sagittarius (adapted from Aladin Lite)

3. Open star clusters. There are many larger and brighter open clusters that are easily visible in even small binoculars. Some of the best are the Hyades and the Pleiades in Taurus, the Double Cluster (NGC 869 and 884) and M34 in Perseus, M35 in Gemini, IC 4756 in Serpens (Cauda), M44 (the Beehive) in Cancer, M23 in Sagittarius, M7 in Scorpius, NGC 752 in Andromeda, NGC 7209 in Lacerta, NGC 6940 in Vulpecula, M46 in Puppis, and NGC 2360 in Canis Major. Many globular clusters can also be spotted in binoculars, but they invariably look like little fuzzballs unless you have very large binoculars.

Above: M35 in Gemini. (Astrophoto Andy, via Flickr, CC by 2.0, brightess/contrast adjusted, cropped and rotated)

4. Asterisms. These are groups of stars that form patterns even if they may not be actual gravitationally bound clusters. You can probably find your own by scanning the sky, and many of them are best seen with the naked eye (Big Dipper or the Plough in Ursa Major, the Backwards Question Mark in Leo, the Keystone in Hercules, the Teapot in Sagittarius), but a couple of the most famous ones for binoculars are the Coathanger (Collinder 399) in Vulpecula, and Kemble's Cascade in Camelopardalis.

Above: The Coathanger asterism. Simulated binocular view.

5. Nebulas. You need a darker sky to view most nebulas in binoculars. Some of the brightest are the Orion Nebula (M42), which will show up even in bad light pollution, the North American Nebula (NGC 7000) and the Veil Nebula (NGC 6992 and NGC 6960, etc.) in Cygnus, the Helix Nebula (NGC 7293) in Aquarius, the Lagoon Nebula (M8) in Sagittarius, and the Dumbbell Nebula (M27) in Vulpecula. If you're in a really dark sky, you might also be able to pick out dark nebulas, which are clouds of obscuring dust that make it seem like there is a ragged black hole in the star field.

Above: The Helix Nebula, NGC 7293. Simulated binocular view adapted from Aladin Lite.

6. Galaxies. Most galaxies are relatively small objects, and some of the smaller but brighter ones can be seen in binoculars. The bigger, brighter ones are the Andromeda Galaxy (M31) in Andromeda, M33 in Triangulum (need a pretty dark sky), and NGC 5128 in Centaurus (if you're far enough south).

Left: Galaxy M33. Simulated binocular view adapted from Aladin Lite.

7. Interesting stars. Many double stars, variables, and colorful stars are good for binoculars. A very steady hold with 10x or higher binoculars will split the colorful double Albireo. Any stars with reasonably close magnitudes with a separation of about 30 arc seconds or more are fair game for binocular observation. You might do better or worse, but that's about the practical limit for most people with 10x binoculars.

Above: Double star Nu Draconis (Kuma). Although this simulated binocular view adapted from Aladin Lite makes it look very difficult to split, at 62.3 arcseconds separation, mounted or steadily held 10x50s can do half that.

8. Asteroids. Asteroids look like stars except they appear to change position over a matter of hours or days, depending on the magnification you are using. Binoculars can be used to view stars and asteroids to approximately 11th magnitude, depending on your sky, your binoculars, your observing experience, and the density of the star field. Here's a list of 25 asteroids that are often viewable in binoculars. Magnitudes of asteroids do vary as they orbit the Sun, so sometimes you can catch dimmer ones during a favorable apparition. Sketch their position from one night to the next to verify you have the right "star." Apps like Sky Safari Pro let you do a canned search on the night's brightest asteroids. I looked at tonight's list, and there are 14 asteroids brighter than 11th magnitude, however not all of them are well placed in the sky to view at any given time.

Above: Asteroids vary tremendously in shape and size. This diminutive walnut-shaped asteroid, Dinkinesh, shows a typically irregular shape. Only the largest asteroids become somewhat spherical, and they are some of the brightest, consistently visible in binoculars, unlike this dinky guy. (NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab/Brian May (yes, the Queen guitarist)/Claudia Manzoni). This is a parallel view stereogram. How to view.

9. The Moon and planets. All eight planets can be spotted in binoculars at different times of the year. You won't see any details (except for Earth!), but Saturn looks oblong when the rings are tilted and you can see up to four of the moons of Jupiter, depending on where they are in their orbits. The Moon supposedly shows 100 craters in binoculars, but I haven't counted, and I think it would drive me crazy trying to sort out the ones in the southern hemisphere. Larger objectives may blow out your vision on the Moon. I can't take the full Moon in my 15x70s without some kind of filter.

Above: Jupiter will show up as a tiny disk with no detail. Up to four moons can be seen, depending on their positions in orbit around the planet. Simulated binocular view.

While some people may observe the Sun with proper filters on their binoculars, I don't recommend it because you are looking in its direction and you can be blinded if you pull the binoculars away from your eyes even momentarily.

Technique

Advanced binocular observers often say you can get steady views and reduce fatigue with proper handheld technique (the way you cup your hands around the binoculars and rest them on your eye socket bone structure, etc.), but most people intuitively gravitate to a technique that works for them. That's the beauty of binoculars. But you still won't get the steadiest views without some kind of mounting (see above). 

Some people also say that they rest their arms on the chair arms to steady the view. Well, I don't know what kind of chair they are using, but for every chair I've ever used, the arms are way too low for that and I end up scrunching way down so my head is where my butt should be. Not comfortable or healthy!

Most multipurpose binoculars have a center-focus wheel that you turn with one or two fingers to focus both eyepieces at the same time. This allows you to quickly refocus for terrestrial viewing and is best if your binoculars are not strictly for astronomy. They will have a diopter adjustment on the right eyepiece that allows you to turn a ring to adjust for the inevitable difference between how your two eyes focus. 

Right: The diopter adjuster ring is usually on the right eyepiece. In the case of these 8x42s, adjustment marks are molded into the rubber armor just below the ring. This binocular also has eyecups that adjust by twisting them in or out for the desired eye relief, great for glasses wearers or to get just the right eye placement.

To use the diopter, first find a bright star field, close your right eye, and use the main focus wheel to focus for your left eye only. Stars should be pinpoints, or at least as small as you can make them. Then, close your left eye and using only the diopter ring, focus for your right eye only. Then look with both eyes and tweak the adjustment as needed.

Left: My 15x70s have individually focused eyepieces.That's true with many larger binoculars made for astronomy or long distance viewing only.

For astronomy, many binoculars focus each eyepiece individually, because once you are focused at infinity, you shouldn't need to refocus. You just turn the ring on the outside of each eyepiece and you shouldn't need to mess with it again. In my experience, individual focusing eyepieces hold their focus better and prevent my obsessive-compulsive tendencies from causing me to be continuously tweaking focus, so I like them better for astronomy.

When viewing a specific object, first look at it or the area with the unaided eye, facing it straight on, then without moving your face or gaze, bring the binoculars up between your eyes and the object. If you consistently have your binoculars too high or too low, make the adjustment until you typically have them right on the object each time. With practice you'll find objects more reliably this way, although it can still be frustrating even with practice. Don't get bent out of shape if you can't find something the first time. You can always scan around and compare the view to a chart to see where you are. Especially in a dark sky, it's easy to get lost among the stars. But that's kind of the point, isn't it!

Reducing glare

Unfortunately, we often have to observe with lights around us, not just skyglow. You can set up some screens or other objects to block out the lights (I'm working on an article for a DIY light screen), but you can't always block all of them. Even in a dark sky there's usually some light somewhere and the general glow from parts of the sky or the Moon.

Above: The Bino Bandit glare shield.

I find the Bino Bandit binocular glare shield to be a worthy investment, despite the relatively high cost for what it is. I've tried making something similar and failed miserably. It's made of neoprene and has two holes in it that stretch over your binocular eyepieces. You can get rubber eyeguards, but the Bino Bandit blocks the light from all angles. In addition, it leaves a little more air around your eyes so the lenses won't fog up as easily, and works with eyeglasses. It's easy to switch it from one pair of binoculars to another. I find it great for daytime viewing, too.

Using filters

Filters have limited use for binoculars, but they can help on certain nebulas. The problem is that they are designed to be fitted at the bottom end of the eyepiece, but with binoculars they must be threaded in front of the eyepiece, if the binoculars even have threaded eyepieces. This degrades the view, but can still help in some cases. I wouldn't buy a filter just for binocular observing, but if you have one for your telescope you might try it out.

If your eyepieces aren't threaded, you can try holding a filter between your eye and the eyepiece, which is not easy to do. A 2" filter is easier. 

Left: A UHC (Ultra High Contrast) type filter on one eyepiece will enhance a bright nebula, and the non-filtered eyepiece will still give you the full star field: the best of both worlds.

If you do have threaded eyepieces, use a UHC narrowband filter and thread it on one of them. This will give you a filtered view that enhances the nebula but dims down the stars in one eye, and gives an unfiltered, fully illuminated view in the other eye. 

I find a UHC filter helps on the larger and brighter binocular nebulas such as the North Ameircan Nebula, the Helix Nebula, and some of the brighter summer southern Milky Way nebulas. I don't have an OIII filter, but you might try that on the Veil Nebula or Helix Nebula if your sky is relatively dark. I can usually see the Eastern Veil from a Bortle 4 or 5 sky without any filter.