Binoculars For Astronomy - Know the Basics

by Aidan James

If you like to look to the heavens even just occasionally get yourself some decent binoculars and indulge in a little binocular astronomy. Think about it, binoculars are inexpensive, highly portable and require no complicated setting up procedure so are ideal for casual astronomy.

Binoculars allow excellent moon views, and great viewing of star fields, comets and even deep sky objects. They are especially useful for beginners as unlike astronomy telescopes they keep the view the the right way up, making it really easy to navigate the skies. With a little practice you can pick out several of the planets and even the larger moons orbiting Jupiter. Clusters like Pleiades look great because the binoculars wide field of view lets you have more of the cluster in view at one time than a telescope would.

So how to choose which ones? Binoculars have two specifications marked on the body of the binocular in the form of 7x 50, where the first number represents the magnification (in this case 7 times) and the second the aperture in millimeters (50mm in this case). When it comes to selecting the right binoculars for astronomy, aperture is the most important feature to think about. The bigger the aperture the more light is captured so the brighter and clearer the image will be. For astronomy use you will need at least 40mm aperture and preferably larger.

You will need a magnification factor of at least 7, maybe up to 10 if you have a steady hand. Any higher than about 10 times magnification and you will need to mount your binoculars on a tripod as the hand shake effect makes it difficult to get a sharp image.

There are giant binoculars available with higher magnifications and apertures which are designed for astronomy use but you will certainly need a sturdy tripod or mount to use them. These can offer excellent viewing up to about 25 times magnification with 100mm apertures.

This brings us to another point, a specification known as the 'exit pupil'. This specification refers to the diameter of the shaft of light that exits the eyepieces and into your eyes. You can easily calculate it by dividing the aperture by the magnification so that 7 x 50 binocular has an exit pupil of just over 7mm. Capturing as much of that as possible is good as it means all the available light is getting to where you want it, i.e.your eye. If you are still in your twenties you can probably use all of that 7mm exit pupil mentioned above as your pupils will dilate to about that size in very dark conditions, however as you get older your pupil does not dilate more than about 4 to 5 mm so large exit pupils are wasted (though it starts to make those 25x 100's look good!).

You might notice another specification marked on the binocular, the field of view (FOV), it refers to the apparent side to side view as you look through the binoculars. It will be expressed as an angle in degrees or a measure such as 340 feet at 1000 yards. For astronomy use we can generally ignore that factor, it really does not matter a great deal at the distances we'll be viewing at.

So now you have the basics why not get yourself some binoculars and indulge in a little casual astronomy, you'll be rewarded with some wonderful sights!

Step-by-Step Guide to Increase IQ

Galileo's Telescope

Galileo Galilee used a basic version of the telescopes that are used widely today. Galileo used a refracting telescope and used two lenses, a concave and a convex lens inside a tube. Convex lenses have edges that curve inwards. That's what the typical magnifying glass uses. Concave lenses, on the other hand, have lenses that curve outward. Some believe that the spy glasses, which were invented earlier and made popular around the same time, inspired Galileo to make his own telescopes.

When the convex and concave lenses are combined together, they are able to magnify distant objects. This is the main principle behind the refracting telescope. These lenses gather and focus light at a point. When light that is collected bends and forms images, refraction takes place.

Galileo used his telescope to view the moon and planets like Jupiter and observe them in detail. Although the images were not sharp, he still was able to draw the moon with its craters. To improve the optical quality of his telescopes, he made his own lenses and was able to achieve a magnification of 9x using them in his telescopes. Today, variations of refracting telescopes exist. The special combination of lenses now make it possible to use a short tube for refracting telescopes. Telescopes have come a long way since Galileo.

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