Guide to Binocular Astronomy

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Astro Dog recently added our first pair of Binoculars to the store, with good reason, and so it’s a good time to talk about the humble Binocular.

It seems obvious, doesn’t it?  If you want to look at the stars, get a Telescope.  Yet – in truth, Binoculars are in fact far more desirable for a beginner, and in fact, even as a beginner becomes advanced, a good pair of Binoculars never go “out of fashion”.  But why is this so?  Is it really reasonable to think that Binoculars are an ideal starting Telescope?

Yes it is.  Binoculars have several fantastic advantages.  They are less expensive than telescopes, and later, when a Telescope is purchased, they can be used in conjunction with a larger instrument (either yourself, or you can take turns with someone else, they use Binoculars, while you use the Telescope, then swap, which is very enjoyable).  They are very portable, available for immediate use and offer very wide views – typically 5 or six degrees.  There are even ultra wide models that give wider views still.  As they use both eyes, they feature improved contrast, resolution and your eyes become more sensitive to light by up to 40%1Mullaney, J. (2007)  A Buyers and Users Guide to Astronomical Telescopes and Binoculars.  Springer : Delaware .  They are free from the complications of using a Telescope, force familiarity with the heavens and build a far better understanding of the sky that Telescopes initially do.  Binoculars can also show you lovely objects in quite a beautiful way – a way that Telescopes can’t.

What sort of objects can you see?  Well, Dickenson and Dyer2Dickenson, T., Dyer, A. (2008) The backyard Astronomer’s Guide. Firefly Books : Richmond Hill. list a few sights, including the star clouds of the milky way, planetary motions, bright comets, lunar eclipses, details of constellations, the moons of Jupiter, dozens of lunar craters, variable stars, double stars and star clusters, several galaxies and nebulas (including the magnificent M42), seven of our planets and bright asteroids (avoid the sun).

What type and size binoculars should you get?  Avoid Zoom binoculars.  A weight between 630grams to 900grams is recommended.  You will need to choose between a low magnification (7-9) and a high magnification (10-15+) pair.  A low magnification pair will give a wider field than a higher magnification, while a stronger magnification will show you fainter stars and the moon in more detail.  Sizes of between 7×50 and 12×50 are popular for observing and usually range from $140 to $400 for a Premium Pair.    Patrick Moore has the proviso that “with a magnification higher than x12, a mounting of some sort is highly desirable”3Moore, P. (1996) Exploring the Night Sky with Binoculars. Cambridge University Press : Melbourne, p. 18.  So, x12 is about the highest to go without a mounting, and at x15, a mounting becomes essential.  As a general rule, the higher the second number (e.g. x40, x50, x60 etc..) the more light is collected, so a x50 is more desirable than a x40 in most instances.  A 50 is sensible for Astronomical purposes and keeps the binoculars light enough to be easily used.  Binoculars that have 7mm exit pupils are ideal as a general rule, but some modern Astronomical thinkers such as Dickinson and Dyer feel otherwise.  I won’t get involved in that debate.

Telescopes do have certain disadvantages or better said – “prerequisites” before your able to be put them to effective use, such as a knowledge of the night sky.  You need to know, for instance, what object do you want to point it at? (You need to know about objects, don’t you?)  Where exactly is that object in the sky?  (You need to know about if the object is up currently, and where in the sky to find it)  Then, you try and find that target using a finderscope (which requires knowledge of how to use it to find objects, something that requires patience and time).  If you have a poor finder, it will be an utter nightmare to find – would you have the experience to understand you don’t have the right equipment, and how to fix it?.  Along with that scenario, goes the stress of putting the Telescope together correctly, putting it on a solid mount, knowing to use a low powered eyepiece initially, not to even mention observing techniques to train the eyes, such as dark adaptation and so on.  In contrast, Binoculars are much simpler to use.  You simply remove the caps, point it up and go.  As you learn more about optimising your use of them, they will bring you extraordinary pleasure.

Jewel Box – Courtesy of Wikipedia

What do we mean by “force a familiarity with the heavens” and “forcing a familiarity with the sky”?  What I mean is this – it is possible to correctly point a telescope at something, and be completely oblivious to what is next to it, or surrounds it, or to see the “patterns” in the sky that you essentially will need later.  Binoculars open up the heavens to you in a very personal and instructive way.  For example, when you look at the Southern Cross with a Telescope, you will see the constellation, of course, but you will struggle to see the things that are so special in it in context.  For example, take a look at one of the most spectacular sights you can see in the night sky – the “Jewel box”.   It truly is a spectacular sight, yet something wonderful happens when you hunt for it and find it sitting next to Crux in your Binoculars.  You know where it is in relation to another constellation, and you remember what’s next to it.  This stimulates your interest in the objects around it.  You will then suddenly see the “coalsack”, and wonder what that is, exploring that delightful object.  You will then know three objects, right next to each other in the sky, and know where they all are in relation to one another – Crux, the Jewel Box, and the Coalsack.  When you then look for a new object, you will find it in relation to where it is compared to these objects (“Ah, Orion is opposite the Southern Celestial Pole sort of…”) and you will start building a familiarity with the sky – however imperfect it may be.  This natural kind of exploring is far superior to the “Okay, seen the Moon, M42 and Saturn, what now?” problem many beginners experience eventually.

But isn’t “building a familiarity with the sky” automatic – even with a Telescope?  It certainly can be, but often isn’t.  Too often, a single object it looked for, identified, and “crossed off” without seeing of even being aware of the exciting bits in between – and this knowledge can be almost bypassed entirely.  Today, it’s possible, using a “Go-To” system to just have the Telescope skew to exactly what your looking for.  And that’s great, but your not looking while it’s skewing are you?  So your not “connecting the dots” between sights and that can set you back in the long term.

Binoculars also have a wider field of view, so there are certain sights that just stand out beautifully when enjoyed with Binoculars.  Bright comets, lunar eclipses, Star clusters such as Hyades and especially Pleiades and both the large and small Magellanic clouds are spectacular when viewed through Binoculars.  So, Binoculars can be fantastic.  What sort should you get?  “Common sense” would dictate you get the biggest you can, right?  Wrong.  These are extremely heavy, and often so powerful that any slight movement (or even seemingly none!) will jump around a great deal not letting you really see much at all.  I would suggest that 12×50 are the largest magnification you should go for – at least if you don’t intend to mount them on something.

So, how are you supposed to use Binoculars?  Greg D. Thomson, in his classic book “The Australian Guide to Stargazing” has the following to say about how to Focus Binoculars and use them correctly.

“To achieve the clearest and most relaxed view through binoculars, move the eyepieces closer together or further apart until they sit comfortably in your eye sockets, allowing you to look straight into them and see no double images…  The large focusing knob on the central rod between both eyepieces provides a change of focus from near to far for both eyepieces.  Relax your eyes and focus with the main focusing knob.  Because many people have a different focus for each eye, most binoculars have a separate focusing capability for each eye.  A secondary focusing mechanism, marked with a scale, is usually provided on the right eyepiece.  To get perfect focus for both eyes, ignore your left eye so as to concentrate on the right eye focus.  Turn the right eyepiece focusing knob until the image is crisp.  Now open both eyes and make any final adjustments to both focusing knobs.  Focus for a relaxed eye to eliminate eyestrain.”4Thomson, D. (2001), The Australian Guide to STARGAZING. New Holland Publishers Australia : Sydney

There is an illusion that you need a Telescope to see the “Best things”.  While it is true that a Telescope is truly wonderful, Binoculars are amazing in their own right.  In fact, Stephen Tonkin5Tonkin, S. (2007) Binocular Astronomy. Springer : Kent,  identifies about 50 sights that you can see with your Binoculars that are truly worth looking at.  This book is available for free to read if you live in Queensland Australia (An upcoming blog will be on free Astronomical Resource Centers where you can get excellent texts).

When you have binoculars, one of the most wonderful objects is the moon.  Fascinatingly, the moon and the sun are both the same approximate size in the sky, which really makes it the “sun” of the night.  There are smooth, creamy broad plains to be seen, mountains that tower up to 6000 meters high that can be seen, ridges, valleys and isolated peaks that are a delight and craters that dwarf anything you can find on the earth.  Be assured that while the moon is very bright, there is no danger to the eye (unless you suffer from a medical condition of some sort perhaps, or you are observing in the day and the sun crosses your path – but then your not looking at the moon, are you?).

Observational Techniques for Binoculars

Actually, these are very similar to those of us that use a Telescope, and can also be used for those who enjoy bino-viewers.

Tonkin6Tonkin, S. (2007) Binocular Astronomy. Springer : Kent, p.106 notes seven techniques that help – he suggests:

  1. Dark Adaptation.  As noted in my previous article on dark adaptation, it take twenty minutes or more for the rods in your eyes to become dark adapted, with further improvements are this time.  So, take the time to become dark adapted.  Tonkin adds a tip to close the eyes for a while before attempting a particularly difficult observation.  Sounds good.
  2. Averted Vision.  You can see more detail if you avert your eyes from the on-axis (straight in the center!) view and “look down toward the tip of your nose so that the light from the eyepiece appears to come from the ‘upper outside’ of the eye”.
  3. Perfect Focus: Ensure that your binoculars are perfectly focused so that you can identify dimmer targets.  Tonkin suggests that independently focusing eyepieces do better at remaining focused.  You may find Thomson’s guide above helpful in achieving the proper focus technique.
  4. Keep the Binoculars still.  Firmly mount the binoculars.  Keep looking, and it may appear.
  5. Jiggle the binoculars!  Combine this with averted vision, and do so ever so slightly and it can make you see something you didn’t notice before.
  6. Breathe.  Helpful at all times, but oxygen really helps the retina perform.  The type of breathing you do shouldn’t involve cigarettes.
  7. Patience and Persistence.  Tonkin and many others note that this, more than anything else, will improve your observations. He notes that it can take several minutes to make a single fleeting observation, and that it can take several attempts over several nights before conditions are right to see your target.

I hope that this has inspired you to give binoculars a go, and I will see you hopefully back for the next one!