When buying binoculars for astronomy one of the main considerations is the light gathering capability of the binoculars you are looking to buy and therefore the size of the objective lens is extremely important.
Before you start check out the range of binoculars for astronomy that are currently on the market you need to consider the distance you are looking to cover and what level of detail you are hoping to see. If you can imagine that a telescope can provide you with a significantly larger aperature (objective lens) and a wide range of magnification abilities it’s understandable that for viewing over longer distances, and to see the finer details, a telescope is often a better option. However that said binoculars can prove useful, even for the serious astronomer, and are an inexpensive way to get started.
The real pro’s of using binoculars for astronomy is the minimal set up time, the relatively low cost, portability and the fact that there isn’t an endless list of accessories that you need to buy.
Manufacturers generally indicate whether or not their binos are suitable binoculars for astronomy but as a general guide you want to be looking for giant binoculars or binoculars with an objective lens that is 50mm or greater. 10×50′s are often a popular choice for astronomy as they are reasonably comfortable to hold yet powerful enough for the basic astronomers needs.
Some manufacturers do make smaller binoculars for astronomy such as the Pentax PCF 8×40 or the higher quality Pentax DCF SP 8×43 and Olympus rate their EXPS I 8×42′s as excellent astronomy binoculars. As a general rule, and particularly relating to the smaller binos, if the objective lens is 5 times or more than the magnification you can use them for astronomy.
