Algedi is October's Star

This month look for the star Algedi in the constellation of Capricornus. Algedi, or Al Gedi, means the Goat in Arabic and astronomers know Algedi as Alpha Capricorni. However, this doesn’t mean Algedi is the brightest star of the constellation. In some constellations, like Capricornus, the stars were named in order of their position, rather than magnitude or brightness. Algedi is one such example. It’s the western most star and therefore received the alpha designation.

The constellation of Capricornus is one of three water constellations in the zodiac. The other two, Aquarius and Pisces, are neighboring constellations. The constellation represents a Sea Goat, or an animal that is half fish half goat (a mixed animals like this is called a chimera). The story behind Capricornus is that the Greek god Pan (who was a satyr or human figure with goat legs) was trying to escape the sea monster Typhon. In his panic, he leapt into the ocean at the same time as he was changing himself into a fish. However, he only completed half of the change and only managed to give himself a fish tail.

Algedi is a double star that is wide enough to see with the naked eye. However, binoculars will bring out the pair even better. Algedi is an example of a double star where the pair is not actually orbiting each other. Algedi is a chance alignment that looks very close together from Earth but is actually hundreds of lights a part. The fainter, more western of the pair is 690 light years away and the brighter one is 109 light years away. Both stars are G class, just like our sun. However, unlike our sun, the two stars are older, larger, and heavier. The fainter left star is larger and brighter then the eastern pair of the stars.  
   
Look for Capricornus and Algedi in the low in the south after it gets dark. The constellation is not bright and there’s only one reasonably bright star in that part of the sky, Fomalhaut. Look for Fomalhaut low in the southeast and then turn your attention slightly higher and to the south. You’re looking for a pattern of stars that looks like a grin. The constellation will stand out, once you locate it.

Algedi in Capricornus the Seagoat