Gamma Virginis
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Virgo |
| Right ascension | 12h 41m 39.6s |
| Declination | -1° 26′ 58″ |
| Apparent magnitude (V) | 2.74 (3.48/3.50) |
| Characteristics | |
| Spectral type | F0 V/F0 V |
| U−B color index | -0.05 |
| B−V color index | 0.36 |
| Variable type | ? |
| Astrometry | |
| Radial velocity (Rv) | -20 km/s |
| Proper motion (μ) | RA: -616.66 mas/yr Dec.: 60.66 mas/yr |
| Parallax (π) | 84.53 ± 1.18 mas |
| Distance | 38.6 ± 0.5 ly (11.8 ± 0.2 pc) |
| Absolute magnitude (MV) | 2.38 (3.12/3.14) |
| Orbit | |
| Companion | Gamma Virginis B |
| Period (P) | 171.37 yr |
| Semi-major axis (a) | 3.746″ |
| Eccentricity (e) | 0.881 |
| Inclination (i) | 146.05° |
| Longitude of the node (Ω) | 31.78° |
| Periastron epoch (T) | 1836.433 |
| Other designations | |
Gamma Virginis (γ Vir / γ Virginis) is a star in the constellation Virgo. It also has the traditional name Porrima.
Gamma Virginis is a binary star, consisting of two stars of approximately equal apparent magnitudes 3.48 and 3.50, and of spectral type F0V. With an orbital period of 168.68 years (calculated by Heintz at Sproul Observatory in 1990) until the beginning of the 1990s it was an easy object for amateur astronomers, but now the smaller apparent distance between the stars requires a larger telescope. The last time they were at periapsis was in 1836. The distance will again be wide enough in 2020 to view with a small telescope. The star system has a combined apparent magnitude of 2.9. The system is 32 light years away from the Sun.
As Gamma Virginis is close to the ecliptic, it can be occulted by the Moon and (extremely rarely) by planets.
Changes of distance and position angle
This table shows the apparent distance between the two stars and their relative position angle: first three columns show data predicted from an orbit calculated in 1937, the next three columns show observations reported by the Hanwell Community Observatory.
| Predicted from 1937 Strand orbit | Observations 2003 to 2005 | ||||
|---|---|---|---|---|---|
| Year | distance | position angle | Date | distance | position angle |
| 1995 | 2.5" | 280 | |||
| 2000 | 1.8" | 267 | |||
| 2002 | 1.5" | 259 | |||
| 2003 | 2003 Dec. | 0.6 arcsec. | 219° | ||
| 2004 | 1.2" | 246 | 2004 Dec. | 0.4 arcsec. | 177° |
| 2005 | 2005 April | 0.27-0.29" | 161±0.6° | ||
| 2006 | 0.8" | 221 | |||
| 2008 | 0.4" | 126 | |||
| 2010 | 0.9" | 44 | |||