Mira (Omicron & VZ Ceti) -- Variable / Double Stars in Cetus
The name Mira translates to “The Wonderful” or “The Amazing One”. This famous star
was easily visible from my suburban home, this morning, even with a bright gibbous
moon nearby. Just 100 days ago this star was so dim that I would have needed a telescope
to see it even from the darkest of skies.
Mira was the 1st star discovered to change its brightness. This Long-Period Variable Star
is 250 times brighter at maximum than at minimum. Mira’s brightness variation is so intense
that its Spectral Type changes from a M5 to an M9 during its 332-day cycle.
Mira is near the end of its nuclear life. This Red Giant star has used up its helium (fused into
carbon and oxygen) and is now entered a “Thermal Pulse Phase”. This phase is short lived,
and Mira will eventually end up as a white dwarf with an impressive planetary nebula.
Currently the star’s pulsations have expanded the size of Mira that if placed where our sun is,
it would engulf the orbit of Mars in visible light and nearly reach the orbit of Jupiter in infrared
Mira is also a double star. Its smaller companion (VZ Ceti) is also a variable star which
changes in brightness from 9.5 to 12.0 magnitudes. It is close enough to Mira that some of
Mira’s expanding atmosphere is being pulled into the smaller blue subdwarf star. In the
drawing it is the star adjacent to Mira at 8 o’clock.