Binocular Tips and Celestial Targets: Using and choosing the right pair for stellar observationSeptember 14, 2018
Most people look forward to getting their first telescope when starting out with amateur astronomy. No one can be blamed either – a good telescope can offer you splendid views of the universe, and is a good investment. Unfortunately, most also overlook just how great of an investment binoculars are to your stargazing arsenal.
In some circumstances, it’s a wise choice for beginning amateur astronomers. They are a more affordable choice, a very portable option, and there is no real set up involved either. This means that getting out and watching the sky is simple and convenient, and so will encourage you to get out there more and really learn to navigate the night sky.
Looking for the Right Pair
Your initial temptation may be to go for the biggest pair you can get your hands on. After all, larger apertures have stronger light gathering properties – and so they reveal more. While this is correct, it is seldom the correct choice to make right off the bat. Just like with telescopes, the bulkier your binoculars are, the less likely you are to use them.
Imagine trying to hold up a very heavy pair of binoculars for an extended period of time: you will tire so quickly, and anything you try to focus on will be a shaky blur as your arms buckle under the weight.
That is not to say that bigger binoculars are a completely bad idea. If you are willing to put a little extra into getting a quality mount for your binoculars, and are comfortable with the set-up; heavier and bigger binoculars can deliver breath-taking results.
Magnification and FOV
Apart from the size and weight of the binoculars, you need to be aware of the magnification and field of view (FOV).
You’ll see three numbers on a pair of binoculars, with two of those numbers forming a set. Common examples of this set include 7 x 35; 10 x 50; and 8 x 40. The first number indicates the magnification of the binoculars, and the second number is the aperture which is simply the diameter of the objective (front) lens in millimetres.
The FOV is usually expressed in angular degrees, ranging from 5 – 8 degrees, and tells you the width of sky the binoculars can see. This is usually comparable to the size of a golf ball held at arm’s length.
Try to go for the largest aperture you can without compromising on portability and ease of use. Lower magnifications actually tend to be better because they allow for more stable views and usually also a wider FOV. To add to that, high magnification but small apertures won’t work, as all the magnification power will do is to brighten and enlarge unresolved objects.
You will also want to look into spending a little extra to get high quality optics that don’t have glaring flaws. It is 100% worth it. Aberration’s when light fails to converge into a single point, and mis-aligned lenses are going to do nothing other than distort views that you can’t get into focus no matter how hard you try, and eventually put you off your new hobby.
Another important determining factor is the size of the exit pupil. When you hold binoculars up, at arm’s length, with the eye pieces facing you, you will notice a round point of light in each eye piece. These are the exit pupils, and generally the smaller they are, the better the quality. It is simple to determine the size of the exit pupils – by dividing the aperture of the objectives by the magnification. For 20 x 50 binoculars the exit pupil is 2.5 mm. The right fit is completely dependent on the individual – children generally have larger pupils, and adults have smaller pupils – even when dark dilated.
If you are buying your binoculars in a store, there is a nifty way of being able to determine some degree of the quality. Hold them at arm’s length above you, with a light source coming from behind you. The binoculars that have the darkest reflections have better optics, and you can see how: there will be far less scattering of light.
On a final note, you may also want to consider sealed, waterproof binoculars if you live in an area prone to humidity.
You have your pair of binoculars, and hopefully you have many nights ahead of stargazing as you learn to explore the night sky – but here are some celestial targets that will make kick-starting your hobby an absolute treat.
Open star clusters are glorious to behold with the unaided eye, and even more wondrous when you point binoculars at them. Binoculars are an even better instrument than telescopes for viewing open star clusters because binoculars offer a far wider field of view, whereas the apparent size of the cluster can’t really be seen within a telescope’s narrower field of view. This means that you can keep most of the cluster in your view, instead of just being able to see small sections of it at a time.
The Pleiades is probably the most well-known and easily recognised of open star clusters. Also known as the Seven Sisters – named for the daughters of Atlas in Greek mythology, and found in the constellation Taurus the Bull, the Pleiades is a treat to behold with binoculars – which keep the full asterism in view and reveal many more stars in the cluster, and the background.
The Beehive in Cancer the Crab is another lovely open star cluster, also visible to the unaided eye. The cluster’s apparent size is quiet big – spanning almost three full Moons across, and lies some 580 light years from Earth. Scanning binoculars across the cluster reveals myriad stars, with a nice interplay of colour – some stars are reddish-orange, and others white-blue.
Looking at the Moon through binoculars allows it best features to stand out. Unlike with a telescope, when the best time to view the moon is at the quarters, full Moon is a good time for taking out your binoculars. Yes, there is still glare, but it isn’t even half as harsh as it would be when viewing with a telescope. It also means that you can observe tonal variations, craters and rays.
Do also take the time to view the terminator at the quarters though, when the contrast between light and dark really makes features pop.
The Milky Way
The wispy, milky band that arches across the sky reveals many jewels when scanned with a pair of binoculars: fuzzy bits in your peripheral vision are revealed to be globular clusters, galaxies, nebula, binary stars and more.
Binoculars may not fully resolve these beauties into well-defined shapes – certainly not the way telescopes can but, they do serve to show you how many wonders lie in the skies above, and teach you how to navigate from one point of the sky to the next.
If you can, having the full experience of being able to view with unaided eyes, binoculars, and telescopes is what you should be aiming for. There are targets that fare better under different conditions: a meteor shower with the unaided eyes; a comet with binoculars, deep sky emission nebulas with telescopes. It also makes for a fuller experience, and a more complete knowledge of the skies. It all starts somewhere though, and binoculars are far more convenient, cost effective, and simpler if you are just starting this hobby.