Mira (Omicron Ceti)
Mira (Omicron Ceti) is a star in the constellation Cetus, magnitude 6.0.
‘The Wonderful’ — a pulsing red giant that swells, fades from sight and returns roughly every eleven months.
In August 1596 the pastor David Fabricius picked a third-magnitude star in Cetus as a reference while tracking a planet. Within weeks it had brightened; by October it had vanished. He took it for a nova — until he saw it again in 1609. In 1638 Johannes Holwarda worked out that it returned every eleven months, and in 1662 Johannes Hevelius named it Mira, ‘the wonderful’.
Mira is a red giant near the end of its life, hundreds of times wider than the Sun. It pulsates, and since most of its light is infrared, small changes in its temperature make huge changes in what our eyes see: at its best it can reach magnitude 2, at its faintest about 10, and its deep red at minimum pales to orange as it brightens. It is the prototype of the Mira variables, of which thousands are now known.
It is not alone. A white dwarf, Mira B, pulls gas from the giant across a bridge of matter seen by the Chandra X-ray Observatory. And in 2007 NASA’s GALEX ultraviolet telescope revealed a vast, comet-like tail of shed gas trailing behind Mira as it speeds through space.
Mira (Omicron Ceti) is 300 light-years away: the light we see from it set off around 1725, 40 years after Isaac Newton published his laws of motion and gravity.
Did you know?
- Herschel’s yardstick for red. When William Herschel described the deep colour of the Garnet Star in Cepheus, he compared it with ‘the periodical star ο Ceti’ — Mira.
- Seen before Fabricius?. Chinese and Korean records from 1596, 1070 and 134 BC may describe Mira, and some lines by Hipparchus might too. None is certain.
- Measured in 1925. In 1925 Francis Pease used an interferometer at Mount Wilson to measure Mira’s size. It was then the second-largest star known, after Antares.
A red star in the neck of Cetus, about six degrees west-south-west of Delta Ceti. Near maximum it is an easy naked-eye star; months later it needs a telescope. Check it every few weeks through its 11-month cycle and watch its colour deepen as it fades.
When and where to see it
It is best placed in the evening sky around November, when it crosses the meridian at about 10 pm local time (around midnight in October). It can be seen from everywhere south of 87°N and never sets south of 87°S.
At its highest it stands 37° up from 50°N, 52° up from 35°N, 87° up from the equator, 58° up from 35°S.
Facts
- Type
- Star
- Constellation
- Cetus
- Designations
- Omicron Ceti, Mira Ceti, ο Cet, 68 Cet, HR 681, HD 14386, HIP 10826
- Magnitude
- 6.0
- Position
- RA 2h 19.3m, Dec −2° 59′ (J2000)
- Spectral type
- M5/6IIIe
- Colour
- orange (B−V 1.10)
- Brightness
- varies from magnitude 2 to 10.1
- Distance
- 300 light-years
- Discovered
- David Fabricius, 1596, Discoverer of its variability
Open AstroPilot to see when Mira (Omicron Ceti) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.