Stargazing with Binoculars

I live in a part of the United States that is relatively far south. As a result, throughout the year I get a chance to see a reasonably large number of constellations, although they are visible for much less time than they would be in the north. On a clear night (and from a high altitude) I can see most of the Argos, although most of its more interesting features and binary systems are unresolvable due to the large amount of atmosphere that scatters the starlight before it reaches me.

Regardless, I’ve had a bit of success using a pair of 16x50mm binoculars to pick out constellations. I think that binoculars offer a significant advantage over telescopes, particularly in urban and other light-polluted areas, because they often can offer equivalent resolution at a fraction of the cost and setup. Having a massive Newtonian telescope will only get you so far if the area that you live in doesn’t have fantastic night skies, so binoculars offer an easy way to learn a lot about the night sky. A good thing to keep in mind when choosing binoculars is that magnification does not matter– it can often even be a hindrance, since your eye is better at picking out details than you might think. Instead, a high magnification instrument is going to be extremely sensitive to minor shaking, making prolonged viewing needlessly tedious. Instead, you want binoculars with a ridiculously high resolution, which is a measure of the ability of an optical device to pick up detail. Think of this in terms of the difference between an iPhone display and an old Gameboy Advance: even though the latter had a much larger screen, you can simply see more on the iPhone because it has a much higher pixel density. Telescopes and binoculars are the same way– their resolution increases linearly with the radius of their aperture (ie, the big lens or mirror that collects all the light), so there’s a tremendous advantage to getting binoculars with large lenses.

Some telescopes on the market, particularly the slender refracting (lens-based) telescopes that you see in department stores, have decently large apertures but ruin them by having a very long body. Long bodies increase the magnification, but also increase optical aberrations like diffraction that degrade the image–resulting in a pitiable final resolution. Instead, the best telescopes and binoculars have very low ratios of focal length (the length the light travels before it reaches your eye) to the primary aperture diameter(the size of the lens or mirror that the light first encounters), a quantity known as the focal ratio . Most binoculars already have low f-ratios, but only fat reflecting telescopes (particularly Newtonian types) have decent f-ratios and thus image quality. Regardless, binoculars are clearly the best bet for amateur astronomy, simply because they are simpler to set up and give your brain two copies of the image to process. The ability to simply point them at whatever you are interested in viewing (and to stabilize them by pressing them against your head) is an additional benefit.

The best things to see with binoculars are open clusters and dense nebulae. M42, the gaseous Great Nebula in the sword of Orion, looks fantastic in the winter– even in the magnitude 4 skies around where I live, I can still still see the gaseous blue halo around the central trapezoid of young stars that comprise the sword. The diffuse blue nebula that surrounds the Pleiades is also visible most nights.

Ptolemy’s cluster in Scorpius is naked-eye visible and even more gorgeous in binoculars, and the Beehive Cluster in Cancer is great on Spring nights. There are lots of others, particularly the double cluster near Perseus and the Coathanger Cluster near the summer triangle, that are also well-suited to binocular observing.

Spring is the best time to view galaxies– while the Northern Hemisphere cannot see something quite as astounding as the Large Magellanic Cloud and its smaller sibling, we nonetheless get a great view of the Virgo Supercluster and Coma Berenices, two regions of the sky densely packed with galaxies(which appear as lovely blobs in the binoculars). M31, our neighboring Andromeda Galaxy, is also a great sight early in the year.

There’s tons of things that can be seen with the binoculars– most Messier objects can at least be discerned with binoculars(after all, our present day binocular optics rival the quality that Messier himself used). Good sources for lists of objects are BinoSky and Skymaps, the latter of which are very useful for finding one’s way around in the dark. If you are interested in showing other people objects through the binoculars, I would highly recommend obtaining a cheap and potentially unsafe imported laser— the green wavelength undergoes Rayleigh scattering at night, and so the length of the beam will be visible as it extends into the sky. It’s great to be able to literally point objects out on the celestial sphere, and the end of the beam can be seen through the binoculars(allowing you to guide observers towards Messier objects).