In 1596, German astronomer David Fabricius noticed a star that seemed to appear, disappear, and then reappear months later. It was unlike anything seen before: not a supernova, not a pulsar, but something new – Mira, the miracle star.
Mira was named by Johannes Hevelius in 1662; it’s the Latin word for astonishing or wonderful (the word is also the source of our word miracle, hence my not at all clickbaity title).
It’s a specific type of red giant. The star is actually expanding and shrinking at an amazing rate – from one peak to the next is 332 days. The temperature of the star changes accordingly (cooler as it expands, warmer as it contracts), and this is what changes its brightness. It was last at peak brightness November 26 last year; the next peak is October 24 this year.
Mira is also shedding plasma as it pulses, leaving a tail 13 light years long. That bow-wave will some day form a nebula. We now know more than six thousand other stars that have the same behaviour – the so-called Mira variables.