Mira A
 Location of Mira (circled) |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Cetus |
| Right ascension | 02h 19m 20.79210s |
| Declination | –02° 58′ 39.4956″ |
| Apparent magnitude (V) | 6.57 (2.0 to 10.1) |
| Characteristics | |
| Spectral type | M7 IIIe(M5e-M9e) |
| U−B color index | +0.08 |
| B−V color index | +1.53 |
| Variable type | Mira |
| Astrometry | |
| Radial velocity (Rv) | +63.8 km/s |
| Proper motion (μ) |
RA: +9.33 mas/yr Dec.: –237.36 mas/yr |
| Parallax (π) | 10.91 ± 1.22mas |
| Distance | approx. 300 ly (approx. 90 pc) |
| Orbit | |
| Period (P) | 497.88 yr |
| Semi-major axis (a) | 0.8" |
| Eccentricity (e) | 0.16 |
| Inclination (i) | 112° |
| Longitude of the node (Ω) | 138.8° |
| Periastron epoch (T) | 2285.75 |
|
Argument of periastron (ω) (secondary) |
258.3° |
| Details | |
| Mass | 1.18 M☉ |
| Radius | 332–402 R☉ |
| Luminosity | 8,400–9,360 L☉ |
| Temperature | 2918–3192 K |
| Age | 6 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Mira /ˈmaɪrə/, alternatively designated Omicron Ceti (ο Ceti, abbreviated Omicron Cet, ο Cet) is a red giant star estimated to be 200–400 light years from the Sun in the constellation of Cetus.
ο Ceti is a binary stellar system, consisting of a variable red giant (Mira A) along with a white dwarf companion (Mira B). Mira A is a pulsating variable star and was the first non-supernova variable star discovered, with the possible exception of Algol.
ο Ceti (Latinised to Omicron Ceti) is the star's Bayer designation. It was named Mira (Latin for 'wonderful' or 'astonishing') by Johannes Hevelius in his Historiola Mirae Stellae (1662). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Mira for this star.
Evidence that the variability of Mira was known in ancient China, Babylon or Greece is at best only circumstantial. What is certain is that the variability of Mira was recorded by the astronomer David Fabricius beginning on August 3, 1596. Observing what he thought was the planet Mercury (later identified as Jupiter), he needed a reference star for comparing positions and picked a previously unremarked third-magnitude star nearby. By August 21, however, it had increased in brightness by one magnitude, then by October had faded from view. Fabricius assumed it was a nova, but then saw it again on February 16, 1609.
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