Binocular Astronomy

By Tim Trott, 3rd June 2010 in Astronomy

Binoculars play a big part in astronomy for beginners and experienced amateurs alike. They are generally cheaper and much easier to use than telescopes and offer a broad range of what's on offer in the nights sky.

In many ways it's one of the purest forms of astronomy - without fiddling around with optics, computerised GOTO mounts and polar alignments, you can just pick up a pair of binoculars and look. What you find is a sky rich in fuzzy nebulae, spiral galaxies, binary stars, planets and of course the craters on the moon. Binoculars are simple to use, yet the rewards they bring are glorious.

A quick browse through various astronomy shopping websites will quickly show a wide range of good quality telescopic equipment available to purchase. For the beginner setting out to explore the sky for the first time and faced with this daunting choice, perhaps the best option before taking the plunge is to start small, or better still, learn one's way around the sky with a pair of binoculars before moving onto a larger, more powerful instrument. Even if you do invest in a large aperture telescope, a pair of binoculars still comes in handy for low magnification reconnaissance of deep sky targets before bringing the telescope to bear.

Binoculars provide a lightweight and mobile way to view the sky.
Binoculars provide a lightweight and mobile way to view the sky.

Portability is a big factor in binoculars favour. It's easy to move to a dark unobstructed spot for a view of something low down with binoculars - a good deal less so with a large reflector! For trips away from home binoculars are ideal and can be carried as hand luggage.

Binocular Astronomy

The choice of binoculars for astronomy is fairly straightforward. Binoculars are described in terms of magnification and aperture. For example 10x50 binoculars have a magnification of 10 times and the main lens (objective lens) has a diameter (aperture) of 50mm. Aperture determines the light gathering ability of any optical instrument. A larger aperture means more light captured.

With an aperture of 50mm, under ideal conditions, the faintest stars will be of magnitude +11.2 so a pair of 10x50's should be able to show you all 109 deep sky objects in the Messier Catalogue.

Keep it Steady

Some binoculars such as 8x40's or 10x50's are comparability lightweight and can be hand held during observing for several minutes at a time. To get a steady comfortable view it's a good idea to prop elbows on a convenient wall or fence, or observe from a garden recliner where your arms can be given a bit of extra support. For longer sessions binoculars should ideally be mounted and one of the simplest methods is to attach them to a camera tripod. Most photographic stores will sell an adaptor and some higher magnification binoculars may even come with an adaptor.
A tripod is a useful accessory to have when viewing binoculars. It eliminates shake and gives your arms a rest!
A tripod is a useful accessory to have when viewing binoculars. It eliminates shake and gives your arms a rest!

With a steady mount you are more likely to see fainter stars and deep sky objects, and resolve finer lunar detail than you would by the hand held route. By the time we get to the realm of larger binoculars like 15x80, weight considerations make tripod mounting essential.

Optics and Mechanics

Like telescopes, binoculars come in a variety of configurations, each of which uses prisms to fold the optical path into short tubes. The most common is Porro prisms in which the eyepieces will appear slightly offset behind the objective lens. Roof prism models have a more strait through layout. Focussing is often done via a central knob and good binoculars will allow independent focussing for either eyepiece - essential for everybody with less than 20/20 vision.

With binoculars (and everything else) you get what you pay for. Top end binoculars will have ED glass optics and high transmission coatings and some may even have image stabilisation built in, but these cost a pretty penny. You can also pick up a decent low magnification pair for less than £20 at the supermarket.

The Binocular Sky

Moon Correctly Orientated
Moon Correctly Orientated
The Moon is the obvious starting point here. It's close, bright and large. Binoculars will clearly show the outlines of the dark Maria against the lighter highlands. At full moon the binoculars are excellent for viewing the bright ray systems emanating from craters such as Tycho or Copernicus. The waxing and waning moons show lots of details in the craters and when the moon is a narrow crescent; binoculars will show the ghostly outline of the moon illuminated by Earthshine.

More powerful binoculars (mine are 15x70) can resolve the larger moons of Jupiter and the rings on Saturn and the phases of Venus. You can't make out any surface detail or the ring divisions, but even so, it's still a great sight. Even the large asteroids Vesta, Ceres, Iris and Flora are visible in 10x50's with some patient observation.

Beyond our solar system, there are still more sights to see. Wide field views are important for variable star observing and there are numerous wide double stars that can be split by binoculars. A good example if the colourful omicron cygni located on cygnus' upper wing where you can see the orange and green components separated by four arcminutes.
A deep-sky exposure of the Pleiades star cluster by amateur astronomer Robert Gendler.
A deep-sky exposure of the Pleiades star cluster by amateur astronomer Robert Gendler.

Messier objects are good targets as well. M45 Pleiades is a prime target, as is the star cluster M24. M42 The great Orion nebula is a favourite of mine and does not disappoint on a dark night. Even galaxies are visible with binoculars. The Andromeda galaxy (another favourite of mine) puts on a good show during the autumn months and can be easier to see in binoculars than a telescope.

  1. Gary

    Hi Tim,

    Thanks for the ideas and reviews. Any suggestions for a mount/tripod for large binoculars? (Sorry, I haven't read everything you've written. Maybe you covered this elsewhere.)

Leave a Reply

Your email address will not be published.