Beginning stargazers are often frustrated when trying to tell a friend how far a night sky object appears to be from another. Just how far apart do Polaris and the Big Dipper seem to be? Inches? Feet? Miles? Without a common frame of reference such measures are meaningless. Nor is it helpful to know actual distances, like an object is 20 light years from another.
Fortunately an easy-to-use method employing degrees to measure angular distances is helpful, not only in expressing distances between objects, but also in indicating sizes (like a constellation) and an object’s distance above the horizon.
From our perspective, the night sky appears as a half sphere, like a giant overhead bowl on which the sky objects are painted. A sphere being 360 degrees around, a half sphere is 180 degrees, thus the angular distance (the distance measured in degrees) across the sky from any point on the horizon to the corresponding opposite point is 180 degrees, and straight overhead (called the zenith) is 90 degrees from the horizon.
This approach gives us that needed common frame of reference, but maybe you’re thinking: "OK, but how can I measure degrees without special equipment?" Well, you’re in luck as there’s a handy (pun intended) method for approximating degrees using your hand held at arm’s length. While it doesn’t give precise values, it works great for casual stargazing.
Holding your hand at arm’s length and closing one eye, the outer joint of your index finger is about 1 degree across. The width of your fist is about 10 degrees across, and a wide open hand-span is about 20 degrees.
We can immediately see that Polaris is some 30 degrees (three fists) from the nearest Big Dipper star, that Orion’s three belt stars span about 3 degrees (three fingers), the Big Dipper is near 25 degrees long, and the full Moon is about 1/2 degree in diameter. And you can tell your friend that interesting object you’re trying to point out to her is about 40 degrees above the horizon. So you do indeed have a most handy measuring device always at your disposal.
* Jan. 25 Tue. morning: The Moon, Saturn, and Spica form a triangle in the south with Spica nearest the Moon.
* 26 Wed.: The Moon is at 3rd quarter.
* 29 & 30 Sat. & Sun. mornings: A crescent Moon is to the right, then below, Venus in the southeast.
* Feb. 2 Wed.: Candlemas, a cross-quarter day celebrating the middle of winter; it’s also Groundhog Day and whether or not he sees his shadow, there will be 46 more days of winter; and the Moon is new.
* 6 Sun. evening: A crescent Moon is to the right of Jupiter.
* 11 Fri. evening: The Moon is at 1st quarter.
Evening: Bright Jupiter in the southwest sets at 10 p.m.
Morning: Brilliant Venus dominates the southeast with Mercury near the southeastern horizon as dawn breaks; Saturn is high in the south.
Stargazer appears every other week. Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th, Waco, 76707, (254) 753-6920 or email@example.com. See the Stargazer Web site at stargazerpaul.com.