When to use binoculars to view the night sky

Binoculars have their place in astronomy, and three of their biggest advantages come down to portability, field of view and price.

With binoculars, you can easily view objects in the night sky like, craters on the moon, the Milky Way galaxy, over 100,000 stars, faint nebulas and distant galaxies.

Binoculars are also very useful given the weight and size; they can be put into a back pack, set on the back seat of a car or carried around you neck without any inconvenience and with limited preparation, compared to a 6”, 10”, 12” or larger telescope.

Excellent quality binoculars can be purchased for a comparatively small amount of money. For instance, a few hundred dollars will buy you a fair quality entry level telescope, whereas, a few hundred dollars will buy you an excellent pair of binoculars, which you will never need to replace.

There are two types of binoculars, those that are handheld and those that are mounted. Generally, handheld binoculars will be lighter and will have less magnification power than mounted binoculars, but will provide a larger field of view of the sky.

When choosing binoculars for astronomy, realize that binoculars which are made for daytime terrestrial viewing won’t suffice for nighttime celestial viewing; however, binoculars made for nighttime celestial viewing will be fine for daytime terrestrial viewing.

Some good size binoculars for most people under 40 years old to consider include those that are 7×50 (7x magnification and 50mm aperture) or 8×56 (8x magnification and 56mm aperture) which both have an exit pupil of around 7mm (exit pupil = aperture / magnification). As people age, their pupils become less well able to dilate, meaning that using binoculars with an exit pupil bigger than the eye’s maximum pupil dilation diameter will cause the image to appear darker, since not all of the light collected by the binoculars is reaching the pupil of the eye. For people over 40-years old, a good size of binoculars to consider are the 7×35 or 8×40, which both have an exit pupil of 5mm.

Binoculars that utilize the porro-type prism are best for space use, as they produce a brighter image than roof-prism binoculars and tend to be a little less expensive, despite being slightly larger in size.