Mira
I often refer to John Goodricke and Edward Pigott of York as
being the ‘Fathers of Variable Star Astronomy’ which they are, but the first
variable star to be discovered was found nearly 200 years before them.
The Dutch astronomer David Fabricius saw a star in the
constellation of Cetus the Whale he recorded it of being of the third magnitude,
which means it is quite easy to be seen with the naked eye, this was of course was
in the days before the telescope had been invented. A few weeks later he could
not find it!
In 1603 the German astronomer Johann Bayer who was producing
his Uranometria star atlas recorded it slightly fainter at the fourth magnitude
and gave it the Greek Omicron. Bayer allotted the brightest star in each
constellation the Greek letter alpha followed by beta the next brightest star and so on until omega. We still use this
system today.
It then vanished again, it was not until 1638 that the Dutch
astronomer Johann Holwarda recognised that the star omicron ceti became bright
every 331 or so days. Sometimes it can become as bright as Polaris the North Star while at its faintest
it drops sown to the ninth magnitude and is a test to find it in binoculars.
Omicron Ceti is the prototype star for a large class of these
so called long period variable stars. These are large red giant stars
approaching the end of their lives.
This was the first time astronomers had seen a star change
in brightness and they were amazed. They
called omicron ceti, Mira which means “The Wonderful Star”.
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