Skywatch Line for Wednesday and Thursday, February 21 and 22, 2024, written by Alan French
This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, February 21 and 22, 2024, written by Alan French.
The Sun rises at 7:18 A.M. on Wednesday and sets at 4:57 P.M. On Thursday it rises at 7:17 and sets at 4:59. This Thursday has 13 ¾ minutes more daylight than last Thursday.
The Moon reached first quarter last Friday and is now headed toward full. At 6:30 P.M. on Wednesday the 94% sunlit, waxing gibbous Moon will be 38 degrees above the eastern horizon. It will be in constellation
Cancer, the Crab. By 6:30 P.M. Thursday, 98% of the Moon’s visible face will be in sunlight, and the Moon will be 27 degrees above the eastern horizon in Leo, the Lion. The Moon will reach full at 7:31 Saturday morning.
Binoculars are handy for exploring the night sky and show considerably more than can be seen by eye. At a site with dark skies, free of light pollution, a person with good eyesight can see about 3,000 stars. Under
similar conditions, binoculars with 50mm objectives have more than 200,000 stars within their grasp. Even the common 40mm aperture binoculars significantly increase the number of stars you can see. Binoculars can also show the brighter and larger deep sky objects, star clusters, nebulae, and galaxies.
The important numbers for binoculars are magnification and aperture. A popular size today is an 8×40, “8 by 40,” a pair that magnifies 8 times and has 40mm diameter objectives. The objective diameter determines how much light the binocular collects. For looking at faint objects in the night sky, larger lenses that collect more light are better, but also heavier. (In the world of telescopes, the diameter of the telescope’s objective determines how much detail it can potentially show. At the low magnifications used in binoculars, their potential resolution is not reached and not a consideration.)
Magnification enlarges objects in the sky, making them easier to see. It also spreads out the sky background, making it appear darker and allowing faint celestial objects to stand out better. Higher
magnifications make binoculars harder to hold steady. (I find shaky views of stars more distracting than shaky daytime views.) Most people find 10x is their maximum, comfortably steady magnification. Others
prefer 7 or 8x. An advantage of lower powers is they produce wider true fields, showing more of the sky. A 7 or 8 degree true field shows a wider view than is available in all but specialized telescopes.
If you wear glasses, you should consider the binocular’s eye relief. This is the distance from the eyepiece you place your eyes to properly see the image and entire field of view. Look for about 20mm of eye
relief. The eye relief numbers tend to be inconsistent and do not tell the whole story, so trying a pair in person may reveal a pair with a smaller value will work for you and your glasses.
Many consider a 10×50 binocular the ideal choice for star gazing, but only if you can hold it agreeably steady. An 8×40 is also a good choice. A big advantage to binoculars, in addition to the compact size and ease of use, is they are versatile and can be used for bird and nature study, some sports events, and other activities. Telescopes tend to be more specialized, although some small refractors and other more compact designs can be used as spotting scopes.