Mira
From Slackerpedia Galactica
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Description
Mira is a hugely big variable star, discovered way back in 1596 by David Fabricius. The star was originally thought to be a nova, but unlike other novae, it reappeared about 330 days later. And 330 days after that. And 330 days after that... This unheard of behavior was considered so weird as to be miraculous, which is where Mira comes from. And now you know... the rest of the story. Oh wait, no, not yet.
A Peculiar Star
Mira, or omicron Ceti is now known as the prototype of a kind of pulsating variable star, known as the Mira variables. These stars have masses around that of the Sun (up to a few times larger), and are at the very ends of their lives, just before they turn into planetary nebulae and white dwarf stars. Their most entertaining trait is that they pulsate; by definition, Mira stars have periods longer than 100 days, and their brightness changes by at least 2.5 magnitudes over one pulsation cycle. A few Mira stars change by ten magnitudes, which is a factor of ten thousand in units of flux. That's close to what classical novae can emit, but Miras do this every cycle.
Observability
Miras are bright giants -- very red, very cool, very very big. Most Miras are probably a few to several astronomical units across. Mira itself is one of the few stars that are resolvable (in a big telescope) -- partly because it's big, but also because it's one of the closest Miras to us. Mira is interesting, too, because it has a little companion next to it. The companion is almost certainly a white dwarf, and is a variable star in its own right with the glorious name of VZ Ceti. Ok, not so glorious, but interesting all the same; its brightness rivals that of Mira at very blue wavelengths because Mira emits so little blue light of its own. If you look at Mira with an ultraviolet filter, you're really looking mostly at VZ Ceti.
Mira, aka omi Cet, is a popular star with variable star observers, as nearly every maximum is observable with the naked eye, and it is within range of binoculars throughout most of its cycle. You should observe it, too. Yes, you. Go look here -- pick up a star chart while you're there, too.
Related Links
AAVSO mention of Mira
Hubble captures Mira
Cool pictures of Mira from Harvard
