Sigma Octantis
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 Octans and around, with Sigma Octantis in the middle marked in cyan. (Click on the image to see it full size.) |
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| Observation data Equinox J2000 |
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|---|---|
| Constellation | Octans |
| Right ascension | 21h 08m 46.8s |
| Declination | -88° 57′ 23″ |
| Apparent magnitude (V) | 5.42 |
| Characteristics | |
| Spectral type | F0 III |
| U-B color index | 0.13 |
| B-V color index | 0.27 |
| Variable type | Delta Scuti |
| Astrometry | |
| Radial velocity (Rv) | +11.9 km/s |
| Proper motion (μ) | RA: 25.96 mas/yr Dec.: 5.02 mas/yr |
| Parallax (π) | 12.07 ± 0.48 mas |
| Distance | 270 ly (83 pc) |
| Absolute magnitude (MV) | 0.83 |
| Other designations | |
| Database references | |
| SIMBAD | data |
Sigma Octantis (σ Oct / σ Octantis) is a magnitude 5.5 star in the constellation Octans.
Its position near the southern celestial pole makes it the southern hemisphere's pole star and counterpart to Polaris, the current North Star. To an observer in the southern hemisphere, Sigma Octantis appears almost motionless and all the other stars in the Southern sky appear to rotate around it. It is part of a small "half hexagon" shape. It is over a degree away from the true south pole, and the south pole is moving away from it due to precession of the equinoxes.
Sigma Octantis is sometimes called Polaris Australis, or South Star. However, it is a faint star—at magnitude 5.5 it is barely visible to the naked eye—which makes it a rather poor pole star, especially by comparison with the much brighter and easily visible Polaris.
Sigma Octantis is the dimmest star to be represented on a national flag. It appears on the flag of Brazil, symbolising the capital city Brasilia.
[edit] References
- HD 177482 -- Variable Star. SIMBAD Astronomical Database. Retrieved on November 5, 2005.
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