The Changing Sky: Mira, a Variable Star

When observing the night sky, I enjoy the slow changes of the seasons and the stars as they arrive into the evening sky. The Moon and planets change their positions regularly, sometimes quite quickly. And transient events such as meteor showers and eclipses bring some drama to the sky. But the backdrop of stars is supposed to be constant and unchanging. And that brings me to the motivator for this blog post, the variable star Mira.

Stars have billion-year life cycles, so for us to witness a star's brightness changing over days and weeks is a rare thing. Astronomers study this special class of stars that regularly vary in brightness, and there is an association, the American Association of Variable Star Observers (AAVSO) that collaborate on research in this field. There's even a cool iPhone app that developer John Rachlin introduced me to. It's called Variable Stars, and it is free.

Mira is a well known variable star, and lately it has been changing its brightness very fast and over an extreme range, so that this star that is normally invisible to the naked eye is suddenly visible in the evening sky. I stepped outside this evening and found it near Jupiter, just a "thumb and a little finger away" as described by astronomy writer Tony Flanders in this Sky & Telescope article. I'm pleased to have found this special star that is now 1000s of times brighter than usual. If you feel up for a challenge, try to find it tonight.

Image courtesy of Sky & Telescope Magazine.