Tonight – April 24, 2015 – the rather wide waxing crescent moon passes in front of the constellation Gemini the Twins. The two brightest stars in Gemini are Castor and Pollux. The other bright star on the other side of the moon is Procyon, the brightest in Canis Minor the Lesser Dog. The king planet Jupiter, which outshines all these bright stars, lies to the east of tonight’s moon. Look for the moon to be closer to Jupiter tomorrow night, April 25.
Beyond the fact that both Castor and Pollux are respectably bright stars, they don’t really look alike. Pollux is golden in color, and Castor is pure white. If you have binoculars, they’ll help you to more easily distinguish the contrast of color.
Castor and Pollux are different kinds of stars. Castor is a hot, white-colored star that is well known for its multiple personality. It consists of three pairs of binary stars – or six stars bound together in an intricate gravitational dance. Pollux is a cool and bloated orange-colored star, said to be the closest giant star to Earth. A star swells up into a giant in its old age.
These two stars – Castor and Pollux – were seen as twins in the star lore of many civilizations. Regardless of the seeming connection between these two stars, Castor and Pollux are not close together or physically related. They happen to reside along the same line of sight.
These stars are extremely noticeable in the night sky. No other two such bright stars appear so close together. Of course, many myths explain their proximity. In most cultures, these two stars were seen as twin stars, usually as heroes.
In Greek and Roman mythology, Castor and Pollux were the twin sons of Jupiter and Leda and brothers of Helen of Troy. They sailed with Jason as two of his Argonauts.
Pollux, represented by the brighter star, was immortal, but his brother Castor was not. When Castor was killed in a fight, Jupiter wanted the two to remain together, so he decreed that they each should spend some time in the underworld and some time in the heavens. This is a fanciful way of explaining why the constellation is above the horizon for part of each day and below the horizon for the rest. Castor and Pollux are sometimes said to represent brotherly love.
Meanwhile, in China, these two stars were associated with water, as part of constellations representing rivers. They were sometimes also seen as the complementary elements of yin and yang.
The moon passes in front of Gemini for a few days every month. The sun, on the other hand, passes in front of Gemini for one month each year, from about June 21 to July 20.
Bottom line: Tonight’s moon – April 24, 2015 – is approaching the stars Castor and Pollux in the constellation Gemini the Twins. These stars represent twins in many cultures. Look for tonight’s moon and contemplate the Gemini Twins! They will become your friends for life.