The value of binoculars
Stephen Tonkin Telescopes aren't the only option for observing astronomical objects
Starting out in astronomy and wondering what to buy for your first telescope? There's a simple answer to that question: don’t buy one, buy two. Two small ones that are joined with a hinge so that the distance between them can be adjusted to exactly match your eyes. We are of course talking about binoculars – a valuable tool in the armouries of most active observers.
There are hundreds of astronomical bodies that a pair of binoculars will bring into view for you. Not only will they let you see many more objects than you can with your naked eye, but the detail and colour in those objects become a lot richer.
With binoculars, Brocchi’s Cluster actually looks like a coathanger and the Orion Nebula becomes a fantastically detailed painting of light. The Milky Way is no longer a tenuous glowing band, but a knotted tangle of stars, interspersed with mysterious dark patches. Albireo goes from being an
From left to right, 8x40, 10x50 and 15x70 binoculars. Ask around to determine which size is best suited to you and the type of viewing you intend to do ordinary-looking star that marks the head of Cygnus to an exquisite juxtaposition of gold and sapphire. And you can easily see galaxies by the light that left them millions of years ago, when our ancestors were barely Australopithecines.
Binoculars are still suitable even if you want to do ‘serious’ astronomy. There are variable star observing programmes specifically for binoculars, and their portability makes them ideal for taking to the narrow track where a lunar graze or asteroid occultation is visible.
Alternatively, you could wrap up warm, lie back on your garden recliner and just enjoy the objects that the binoculars let you find as you cast your gaze among the stars. Before you realise it, you have begun
to learn the sky and you’ll soon be able to navigate around it better than the entry-level Go-To telescope you nearly bought instead.
Best of all, you can have this complete observing system for two eyes for less than the price of one reasonably good telescope eyepiece.
What to look for
Binoculars are classified by two numbers that refer to their magnification and aperture. So a 10x50 pair of binoculars has a magnification of 10x, and each of the objective lenses has an aperture of 50mm. These numbers also enable you to calculate the size of the circle of light – or ‘exit pupil’ – that emerges from the eyepieces: all you have to do is divide the aperture by the magnification. So a 10x50 pair of binoculars has an exit pupil of 5mm. The exit pupil should be no larger than the dark-dilated pupils of your eyes: anywhere between 4-6mm is fine for your first pair of binoculars.
Larger apertures potentially show you more, but may need mounting