Learning some Astronomy

A large hurdle in recognizing constellations is determining how large of an area in the sky the constellation takes up. If you look closely at your star atlas, you can find out how big the constellations are as measured in angular degrees. Since the stars are light years away, there is no way to measure their distance from one another, so way must express their relationships in angular degrees of separation. The ancient Babylonians figured out that the sun takes 365 days to move completely around the background of the sky. It is by their definition that the sun appears to move about one degree a day in relation to the other stars in the sky.

Today, we still use their method of dividing a circle into 360 degrees. You can quickly find your way around the heavens with nothing more than your hands. Make a closed fist and hold it at arm's length. This is your measure of 10 degrees. Don't worry if you have big hands. God gave you long arms to match, so this will still work. This all works for little kids too because their little hands are matched with short arms. Starting at the horizon, pace off fist over fist until your reach the zenith. Counted nine 10-degree fists? Turn around and work your way back to the other horizon. Another 90 degrees? 180 degrees from horizon to horizon? Half a circle? Hmm. It works... You can estimate smaller amounts of angular separation. Try gauging the distance between the lower rear star of the Big Dipper to the upper right star the forms the spout. Your thumb's width at arm's length subtends about 2 degrees. 5 thumbs would suggest 10 degrees. Check your atlas! If you hold up your pinky, you can just cover the full moon. 1/2 degree! Experiment: Is the moon actually larger on the horizon than near the zenith? Use your new celestial protractor to find out.

pinky - thumb (Hang-ten!) = 20d
index - pinky (Devil's Horns) = 15d
fist = 10d
3fingers (Boy Scout Salute)= 5d
Pinky alone = 1/2 degree

Armed with your new found knowledge or how to use your hands to feel your way across the sky, your star chart takes on new meaning. Even a little 5 inch planisphere becomes useful: Dial-in the date and hour, figure that from edge to edge the little map shows 180 degrees. Visualize a halfway line cutting the map in half. Two ninety degree segments. Pick one of those and divide it in half-45 degrees. Now that segment in thirds-15 degrees each. If you make a fist and then extend your index and pinky fingers you have a 15-degree measure to match your 15-degree segments on the planisphere. Count the number of closed fists between Arcturus and Vega. Six? Count the number of finger-extended-15-degree-measures. Four? Twenty degrees from Vega towards Arcturus is the Keystone of Hercules. Another twenty degrees puts you smack dab in the middle of Corona Borealis. Count off another 20 to get back to Arcturus.