This is Dudley Observatory’s Skywatch Line for Friday, February 12, through Sunday, February 14, 2016, written by Alan French.
A waxing crescent Moon graces the evening sky. As it moves toward first quarter, occurring very early on Monday, you’ll find the crescent moving higher each night this weekend and more of its face will be in sunlight. The Moon will set at 10:28 pm Friday, 11:38 pm Saturday, and 12:46 am Monday morning.
As we’ve often mentioned, the time around first quarter Moon is ideal for exploring the Moon with a telescope or binoculars. The shadows along the terminator, the line of sunrise marching across the Moon, are long and detail there stands out in bold relief.
Binoculars are superb tools for exploring the night sky. Except for some specialized telescopes, called Rich Field or Richest Field Telescopes (because they show many stars in a single view), most telescopes show no more than about two degrees of sky at once – four times the apparent diameter of the Moon. Larger telescopes are even more restricted.
In contrast, a typical binocular can show 5 to 8 degrees of sky, encompassing six to sixteen times as much sky as a telescope showing two degrees of sky. This makes binoculars ideal for exploring the rich star fields of the Milky Way, wide swathes of sky, and for the occasional bright comet.
Binoculars are really two small, low power telescopes, with additional optics (prisms) to provide a view with the same orientation you see by eye. By contrast, astronomical telescopes invert the view, showing the world upside down, or reverse the world, showing a mirror image of what we see by eye. For viewing sights in the night sky, this is not an issue, but it can be for bird watching and nature study. Indeed, birding and terrestrial telescopes have additional optics to obtain a corrected image, matching that seen by eye.
Many people have binoculars, and if you’re in this group, make a point of using them to enjoy the Moon this weekend or explore the night sky from the comfort on a reclining lawn chair on a clear, dark night from a location away from city lights.
Binoculars are advertised by two numbers, such as 8×42 or 10×50. The first is the magnification and the second is the diameter of the front lens (aperture). For general use, including exploring the night sky, a 7 or 8 power pair is ideal. While higher powers might sound tempting, the field of view gets smaller and they become more difficult to hold steady – which is very noticeable when star gazing.
The diameter of the front lens determines how much light they collect, so bigger is better, especially for astronomy. Today’s various 8×42 models, popular with birders, are a good choice.