365DaysDate: May 4, 2009

Title: Don’t Forget your Binoculars


Podcaster: Robin Scagell

Organization: None

Description: Almost every amateur astronomer has binoculars, and many people advise you to buy binoculars before bothering with a telescope. But is this the best advice, and will you ever be happy without a telescope? Robin is the author of ‘Stargazing with Binoculars’ and looks at the pros and cons of binocular observing versus buying a telescope, with some tips on how to get the best out of your binocular observing.

Bio: Robin Scagell is a British author and broadcaster on astronomy, and runs Galaxy Picture Library. He is Vice President of the Society for Popular Astronomy, and Chairman of the West of London Astronomical Society.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Clockwork Active Media Systems. Clockwork invents, designs, develops and maintains web applications that market, sell, streamline, automate and communicate. Visit or email to get started on your web project.

Transcript: Hi. I’m Robin Scagell

Books on practical astronomy often say, before you buy a telescope, get binoculars. Binoculars are great value, they show a lot and they’ll keep on being useful even when you have got your telescope. But then someone who sells both binoculars and telescopes told me that the advice doesn’t really work. You’ll never be happy until you have got your telescope. So should you start with binoculars or are they just a poor man’s… pardon me, poor person’s second best? And what size of binoculars should you buy anyway?

Let’s start by taking a look through ordinary binoculars, say 8 or 10 magnification, at a variety of objects in the sky. The Moon becomes a world instead of a disc in the sky and you can see its craters and mountains very clearly.

You can pick out all the major features, and craters down to maybe twenty miles or so across. If you decided to draw what you can see, you’d have to pick a very small area to avoid being swamped with detail. You can get to know the Moon very well using binoculars alone.

The planets. Venus is clearly a crescent, when it’s close to us, which is for about a month or so in every year or thereabouts. Mercury and Mars, just dots though.

Jupiter, well, you can see that it’s a disc and not a dot, though there are no features visible in binoculars, but you can spot the Galilean moons very clearly, and see them orbiting the planet just as Galileo himself did in 1609.

Saturn, well, there’s a bit of a challenge. Right now in 2009 it does appear as a dot because its rings are almost edge on to us, but in a year or two you’ll be able to see that it isn’t quite round but is elongated. But that’s not the same as saying that you can see the rings. Galileo couldn’t make them out either.

The outer planets, Uranus and Neptune, well, they’re just dots again, but then they’re not much to look at even with a telescope so you’re not missing much. Asteroids are also dots like they are in a telescope, so again you’re not missing anything except for seeing the fainter ones.

Now comets, that’s another matter. A large and bright comet really is best seen through binoculars rather than a telescope, because it’s too large for the field of view of most telescopes. But bright comets are few and far between. With the fainter comets, the sort that turn up a few times each year, it rather depends on how good your skies are. Faint comets are easily wiped out by a bit of light pollution and haze, but from a good country sky you can often see them.

Going beyond the solar system into what we call the deep sky, binoculars are really great for just scanning along the Milky Way, and for seeking out the larger star clusters. But if your skies are so bad that you can’t see the Milky Way, which probably means most of us, they can help you find the bits of constellations that are invisible to the naked eye. These days, you can’t see some constellations at all unless you live in the country. Take the constellation of Cancer, for example. For many suburban observers there’s just a blank bit of sky between Leo and Virgo, but with binoculars you can find the major stars of Cancer quite easily, and see theBeehive star cluster, M44.

Most constellations are too large to fit into the field of view of binoculars, but with a bit of practice you can find their major stars. In Aquarius or Pisces, for example, you can see the asterisms of the Water Jar and the Circlet, which consist of 4th magnitude stars and need fairly good skies to be seen easily.

This ability to show stars fainter than we can see by eye is one of the great things about binoculars. It’s no accident that most finder telescopes, the little scopes you see on the sides of bigger ones to help you find objects, usually have the same sort of specifications as binoculars — about 8 magnification, and about 50 mm aperture, known as 8 x 50. That’s why I prefer an optical finder on my telescope to the red-dot finders so many telescopes have these days. In a poor sky, optical finders show you the fainter stars and maybe even the object you want to observe.

And the Universe really opens up when we look through binoculars. The bright deep-sky objects such as the Orion Nebula and the Andromeda Galaxy show up in all but the worst skies. And a surprising number of fainter objects come into view as well. This is where I need to talk a bit about magnification. If you’re after the really large and bright objects such as the Beehive Cluster or the Lagoon Nebula, ordinary daytime binoculars work fine. But if you want to go deeper, and seek out the smaller and fainter objects, you usually need more magnification. With a telescope of course you can just use a different eyepiece, but usually you need a second pair of binoculars for higher magnifications. The higher power really does make a difference. I’ve tried to find the Crab Nebula from my home using 10 x 50 binoculars and failed, then as soon as I switched to 12 x 45s, I could see it even though they had a smaller aperture. Not spectacular, but it was definitely there.

Higher-power binoculars open up the range of objects you can find, and you can start to look for galaxies such as M65 and M66 in Leo; galaxies in the Virgo Cluster, which are about 50 million light years away; or the larger planetary nebulae in our own galaxy, such as the Ring Nebula. I’ve found very little difference in the visibility of faint objects between 15 x 70 binoculars, which these days are available very cheaply, and 20 x 60s. The higher power of the 20 x 60s makes up for their smaller aperture, though there is a limit and I wouldn’t recommend 40 x 30s, for example, even if they existed, because they would have such a small field of view as to be very hard to use.

This is why I don’t think it’s a good idea to get high-power binoculars as your first instrument, as a sort of halfway house between ordinary general binoculars and a telescope. The more magnification they have, the smaller their field of view and the harder they are to hold steady. They would be a bit of a challenge to a beginner. But actually 12 x 45 or 12 x 50 binoculars do give you something of both worlds, so I think they are probably a good compromise though if you’ve already got 10 x 50s or smaller then you can still get very good use out of them.

The great thing about using any binoculars is that they really help you to learn the sky. While other folk with computerised scopes are still trying to align them, or complaining that they haven’t brought the power lead or the batteries have failed, you just lift your binoculars to the sky and are observing galaxies and clusters within seconds. Then when you do get a telescope, you already know your way around the sky. So don’t forget your binoculars, and really make friends with the sky.

End of podcast:

365 Days of Astronomy
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