The capabilities of binoculars as astronomical instruments are often underrated by backyard astronomers, especially beginners.
Many beginners wrongheadedly purchase a telescope without ever turning binoculars to the night sky, thinking that only a telescope can truly reveal the cosmos. And yet, binoculars can reveal a multitude of objects completely invisible to the Naked eye: nebulas (star-forming regions), wispy remnants of ancient Supernovas and star clusters ranging from bright stellar splashes to dim Patches of starlight. More challenging are the galaxies, great islands of Stars like our milky way galaxy that dot the void of deep space.
Here’s a list of some of the celestial objects that binoculars can reveal:
- In a dark, moonless sky, ordinary binoculars can pick up more than 100,000 stars, compared with the 3,000 or so visible to the unaided eye.
- Star colours are more evident with binoculars than without, ranging from blue to yellow to rusty orange.
- Any night that the planet Jupiter is visible, two to four of its large moons can be seen close beside the brilliant planet.
- The planets Uranus and Neptune are easy targets with binoculars when you know where to look.
- The Andromeda Galaxy, a huge city of stars larger than our entire Milky Way Galaxy, is plainly visible as an oval smudge near overhead in autumn and early winter for northern-hemisphere observers.
- Star clusters of exquisite beauty, such as the Pleiades and Hyades, are seen in their entirety in binoculars, whereas most telescopes (because of their smaller fields of view) can show only portions of them.
- On the Moon, at least 100 craters and mountain ranges, as well as subtle shadings on the flat plains that 17th-century astronomers thought were seas, are all evident.
- Planets hidden in twilight glow are most often first detected by sweeping with binoculars.
- Earthshine on the Moon (the faint illumination of the Moon’s nightside) is greatly enhanced by binoculars.
- There is no better instrument than binoculars for watching a lunar eclipse, for monitoring a planet’s motion through a constellation over weeks or months or for observing a bright comet.
Two Types of Binoculars
All modern binoculars are instantly distinguished as falling into one of two optical categories: porro prism (left) and roof prism (right). The two examples shown at right are 7×50 (porro) and 8×40 (roof). Personal preference plays a large role in selecting one over the other, but quality glasses of both types perform very well in astronomy.
Other than the fact that light follows different paths due to the prism design, the main difference between the two designs is that roofprism models are more compact than the porro-prism style. But they are also generally more expensive. Personal preference is often the final arbiter.
Adaptability and Flexibility
Most binoculars today are designed with soft rubber eyecups that fold down for observers wearing eyeglasses. Some models prove to be more comfortable than others in this mode, so it is wise to test before buying. The binocular tripod adapter (at right) is an L-shaped accessory bracket that screws into a hole at the front centre of the glasses. Often a threaded cap conceals the threaded hole. Look for it, because not all binoculars are readily tripod-adaptable.