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The famous variable star Mira (Omicron Ceti) has just peaked at the end of September 2011 and for the next few months will be easily visible as an "extra naked eye" star in the Constellation of Cetus.

This years peak occurred around the 24th September 2011 when Mira reached about magnitude 2.4 and for the next few months it will gradually decrease in brightness until hitting minimum about half a year later. The minimum magnitude is usually of the order of 9 so observers will require at least a good pair of binoculars and dark skies to spot it.

It is fascinating to follow a star through such an extreme brightness range, from brilliant naked-eye visibility to the edge of binocular visibility in only a matter of a few months. So don’t miss Mira this year as it is well placed for observation.

Image of Mira from the Hubble Space Telescope (NASA)

There are not too many bright stars in the constellation of Cetus so locating Mira at peak is easy. This year brilliant Jupiter at magnitude –2.9 is also close by.

The variation curve for Mira is not uniform. The star climbs very quickly from minimum to maximum brightness over a period of about a month and then takes a much quieter route on the downward slope, requiring another 6 months to reach minimum. A nice practical task for observers is to plot a light curve, showing apparent magnitude of Mira against time. The finder and comparison chart below can be used to locate and estimate Mira's brightness.

Mira Finder and Comparison Star Chart

Mira Finder and Comparison Star Chart - pdf format

Mira is the prototype of the pulsating red giant stars that vary by at least one magnitude over a period ranging from 80 to more than 1,000 days. These stars have a mass of less than two solar masses, which are coming to the end of their lives. There are at least 6,000 known Mira type stars and all will eventually form a planetary nebula with a white dwarf at the centre.

Mira Data Table

NamesMira, Omicron Ceti, Wonderful Star
RA (J2000)02h 19m 20.8s
DEC (J2000)-02d 58m 39.5s
Apparent Magnitude Range (var)2.0 to 10.1
Period (days)332
Distance (light-years)420
Spectral type M7 IIIe