Courtesy of EarthSky
A Clear Voice for Science
The big and bright waxing gibbous moon erases many stars from the blackboard of night tonight. Nonetheless, the two brightest stars in the constellation Gemini the Twins – Castor and Pollux – should be able to withstand the moonlit glare. The moon is near with Castor and Pollux this evening.
However, you can’t count on the moon to guide you to Castor and Pollux every night. Tomorrow, at this same time, you will see Castor and Pollux in about the same place in the sky, but the moon will be closer to the planet Mars.
The moon travels about 1/2 degree eastward in front of the stars every hour. In one day, the moon goes on the average 13 degrees eastward in front of the stellar backdrop. For reference, the moon’s diameter equals 1/2 degree, and your fist at an arm length spans 10 degrees of sky.
For many, Orion the Hunter is an easy constellation to find. If you can locate Orion, you can always star-hop to Castor and Pollux. Draw a line from the top star of Orion’s Belt (Mintaka) and through the star Betelgeuse, going some 4 times the Mintaka-Betelgeuse distance. Try it tonight. Then try it again tomorrow, when the moon doesn’t reside in the same place relative to the background stars.
Written by Bruce McClure