The twins of Gemini have some bright visitors tonight — the gibbous Moon and the planet Jupiter. They’re all in good view by about 10 o’clock. Jupiter is close to the upper left of the Moon and looks like a brilliant star. The twins of Gemini — the stars Pollux and Castor — stand to the left of Jupiter.
Jupiter and the Moon both stand within the borders of Gemini. The classical constellation is a stick figure that represents two men standing side by side. That figure extends above Pollux and Castor as they rise, and below them at dawn tomorrow.
In the 1930s, though, professional astronomers adopted a new method of defining the constellations. They adopted 88 official constellations, each with well-defined borders. That turned the sky into a patchwork quilt. Each patch is a different size and shape. Like Gemini, some of the patches contain bright, prominent stars. Others are barren, so you need really dark skies to see much of anything.
This system gave astronomers a common framework for describing the positions of celestial objects. The pros don’t use that framework as much today. Instead, they usually refer to an object’s celestial coordinates — the equivalent of its latitude and longitude. But the constellations remain — a legacy of our long skywatching heritage.
Again, look for Gemini in the eastern sky in late evening, highlighted by its bright twins and its brighter visitors — Jupiter and the gibbous Moon.
Script by Damond Benningfield, Copyright 2013