Gettng Started In Binocular Astronomy

See the heavens in stereo

Look up and reap the rewards of viewing the heavens with a modern Binocular. Here's what you need to know to get the right gear and get started.

Astronomy with the modern binocular can be a fun and rewarding hobby. With a small pair of 7x35 binoculars one can gaze the vast star fields in our Milky Way galaxy, track satellites and the ISS across the sky. Sweep the night sky for bright comets, view the annual meteor showers and see the glow of the northern lights (Aurora).



Larger binoculars with objectives of 50mm, 60mm, 70mm, 80mm and 100mm can see Lunar surface details that feature hundreds of craters, mountains, mares, valleys, and rays structures. One can view the surface of our star, but “Caution should be taken when viewing the Sun without the proper protection (solar filters) for your eyes or binocular.”

You can record the daily number of sun spots, view their life cycles, and track their progress around the sun. Occultations of the Moon, planets and stars are well worth viewing along with estimating the brightness and dimness of variable stars. Planets are also great objects for binoculars. You can watch the phases of Venus, view the dance of Jupiter’s four brighter moons orbiting around her, track the procession of Mars and Saturn among the stars.



In darker skies, away from the glow of city lights, the brighter deep sky objects are in the realm of the larger binoculars, nebulas, star clusters and galaxies are jewels and marvels to look at. Examples are M-45 (open star cluster) in Taurus, M-31 (galaxy) in Andromeda, and M-13 (star cluster) in Hercules.



An Astronomy Binocular Primer   

There are some important features and terminally you should be aware of when choosing your binocular for astronomy or in general.

Magnification is the first number and indicates the binoculars eyepiece (power). Example, in a 7x35 binocular the number 7 denotes how much larger an object appears when viewing it through the binocular compared to the naked eye. Depending on the binocular, magnification can range from 2x for opera glasses thru 50x on fixed power astronomical binoculars and over 120x on binoculars equipped with zoom eyepieces.

Objective Lens is the second number and is measured in millimeters (7x35). The 35mm is the size of the back objective lens. The objective lens can range from a small 20mm all the way up to 150mm in size. Objective lens can be made of various glass types but HD and ED glass are better and will help in contrast and color correction.

Prisms There are two types of prisms used in binoculars one is porro and the other is roof.
Porro Prism binoculars have their objective lenses more widely spaced than the eyepieces. They usually give you a wider field of view and a richer depth of field.

Roof Prism binoculars have their objectives in a straight line with the eyepieces. They offer a compact more stream like look and feel they are a favorite with the birders.

Eye Relief, without going into much detail, is the distance from the outer surface of the eyepiece lens to the position where the exit pupil is formed. This measurement is important for eyeglass wearers because they usually need this between 15mm to 20mm.  If the eye relief is too short they may get vignetting in their field of view.

Lens Coating will make a difference in image color, resolution, and contrast. Lens coating are very important because 5% of the light can be reflected off each uncoated glass surface. Look for fully coated or fully multi-coated labeled binoculars, for your best choice.

Field of View is determined by the design of the binocular and can be measured in either feet at 1000 yards or in degrees 7°. Example, 8x42 binocular has around 340 feet at 1,000 yards or 6.5 angular degrees. Binoculars having a field of view 380 feet at 1,000 yards or above are considered to be wide field binoculars.

Close Focus is measured in feet. A binocular with a 6 to 8 feet focus is considered good and liked by many birders. Astronomy binoculars, on the other hand, can have a close focus of 25 to 75 feet depending on the objective and magnification.

Interpupilary Distance is the distance between the centers of the left and right eye pupil. If this is off, you may see a double image or shadows.

Exit Pupil is the diameter of the light cone (expressed in millimeters) that exits a binocular eyepiece. This is important when you get older because our eyes' pupils cannot open as much in low light. After the age 40 an exit pupil of 7mm typically does us no good and we waste the coming light into the eyes.  So we need to find a binocular that will get us around 5mm or under. To get the exit pupil of a 7x35 binocular you divide the objective lens 35 by the (power) 7 equals 5mm (35/7=5) for a 7x50 its is 7mm (50/7=7).




When observing with binoculars you need to consider other accessories that would make your viewing more enjoyable. A good and sturdy tripod is a must for long observing periods and for the heavier binoculars. Consider these support products from Vanguard, Davis & Sanford and Flashpoint. The Star Bound Viewing Chair will help your back and is a very comfortable astronomy chair.

Other items to consider are star charts. These can be viewed and printed from the web; see Astronomy and Sky & Telescope or apps for your smart phones.  A good book on observing is Binocular Astronomy by Crossen/Tirion. This book includes star charts and photographs created strictly for the binocular viewer. A good astronomy flashlight is also needed for viewing chart and books. I use one from Rigel System called the Skylite. This flashlight has both red and white LEDs that are adjustable.
In conclusion, binoculars are an ideal tool for the traveling astronomer and nature lover.   The wide field views will keep you in awe when exploring the wonders of night sky.  Keep looking up!


Keep the conversation going! What's the coolest thing you've seen with your astronomy binoculars? Leave a comment below!

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