One of the most interesting variable stars, omicron Ceti, is currently easy to spot in the night sky, after peaking at magnitude 2.3 in mid-August.
The star, also known as Mira, meaning “the wonderful”, is now fading again. But it rises earlier in the night, making this a good opportunity for many to seek it out.
Mira is a long-period variable with a remarkable range. It can reach second magnitude at brightest, as it did this summer, but then fade to 9th or 10th magnitude when it can only be seen with binoculars or a telescope.
This whole cycle from one peak to another takes around 332 days, or approximately 11 months. Mira becomes the brightest of any variable star in its class.
The extreme observed range of brightness for Mira is 1.7 at its maximum and 10.1 at minimum. The star lies around 420 light-years from Earth.
Latest estimates (early September) put Mira at magnitude 3, so it has become about half as bright as it was at its peak. Over the coming months, Mira will fade well below the limit of naked-eye visibility.
So this is a great opportunity to follow that fade to see for how long you can see it with your eyes alone, and then to watch its continued dimming through binoculars.
Mira lies in the constellation of Cetus, the sea monster. It rises in the late evening in early September and will rise earlier still as the weeks go by. You can find charts to help you locate Mira on the SPA Variable Star Section’s special page, together with a list of stars with which you can compare its brightness.
Mira’s variability is said to have been first noticed by the astronomer David Fabricius who mistook it for a nova in 1596. However, its name suggests that ancient astronomers must have been aware of its stellar performance!