Spica (Alpha Virginis)
Coordinates, Hipparcos distance (250 ly), 4.01-day close B-star binary, precession discovery history, and observing guide for Spica.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Combined apparent visual magnitude (V) | 0.97 mag | 0.95 to 1.05 mag | Photoelectric V-band photometry (ellipsoidal + Beta Cephei modulation) | definitive | Hipparcos New Reduction Catalog |
| Heliocentric distance | 76.6 pc | ± 3.9 pc | Hipparcos New Reduction + Narrabri/NPOI interferometric orbital parallax (J2000.0) | high-confidence | Hipparcos New Reduction Catalog |
| Binary orbital period | 4.0145898 d | ± 0.000001 d | Spectroscopic radial velocity & apsidal motion tracking | definitive | SIMBAD Astronomical Database (CDS) |
| Primary component mass (Spica A) | 11.43 M☉ | ± 1.15 M☉ | Double-lined spectroscopic + interferometric orbit (Spica B = 7.21 ± 0.75 M☉) | high-confidence | SIMBAD Astronomical Database (CDS) |
| Primary effective temperature | 25300 K | ± 500 K | UV & optical non-LTE B-star spectroscopy | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Spica (Alpha Virginis Ellipsoidal Binary) at RA 13h 25m 11.58s, Dec -11° 09′ 40.8″ within Virgo, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Spica (Alpha Virginis) is the brightest star in the zodiacal constellation Virgo and the sixteenth-brightest star in the night sky at magnitude 0.97. Around 129 BCE, the Greek astronomer Hipparchus of Nicaea compared his measured ecliptic longitude of Spica during a lunar eclipse against observations made 160 years earlier by Timocharis of Alexandria, discovering that the vernal equinox slips westward along the ecliptic by roughly 1° every 72 years—the discovery of the precession of the equinoxes.
Located 76.6 ± 3.9 parsecs (250 light-years) away, Spica is an ultra-tight double-lined spectroscopic binary consisting of two hot blue-white B-type stars orbiting their common center of mass once every 4.0146 days at a separation of only 18 million kilometers (0.12 AU). Because the two massive stars sit so close together, mutual tidal gravity stretches both components into egg-shaped (prolate) ellipsoids.
As the tidally distorted pair revolves, Earth alternately views their broad sides and their narrow ends, producing a smooth 0.03-magnitude 'ellipsoidal variable' light curve every two days. The primary star, Spica A (11.4 solar masses, 25,300 K, 20,500 solar luminosities), is already massive enough that it will eventually end its life as a core-collapse Type II supernova.
Practical Visual Observing Guide
- Extend the Big Dipper handle's curve ('arc to Arcturus, then spike to Spica') 30° south from orange Arcturus to pure blue-white Spica.
- Lying just 2.06° south of the ecliptic, Spica is frequently visited by the Moon, Venus, Mars, Jupiter, and Saturn.
- Spica also serves as the southern anchor for star-hopping 15°–20° north into the heart of the Virgo Galaxy Cluster around Messier 87.
Catalog Cross-Identifications & Aliases
Common Aliases: α Virginis · HD 116658 · HIP 65474 · 67 Virginis
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 65474 |
| HD | HD 116658 |
| SIMBAD | * alf Vir |
| WIKIDATA | Q13008 |
Related Objects, Comparisons & Guides
Arcturus (Alpha Bootis Red Giant)
Coordinates, Hipparcos distance (36.7 ly), magnitude −0.05, halo-stream kinematics, and observing guide for Arcturus in Boötes.
Messier 87 (Virgo A Giant Elliptical Galaxy)
Coordinates, distance (16.4 Mpc / 53.5 Mly), EHT 6.5-billion M☉ black hole M87*, relativistic jet, and observing guide for Messier 87.
Sombrero Galaxy (Messier 104 / NGC 4594)
Coordinates, TRGB distance (9.55 Mpc / 31.1 Mly), edge-on dust lane, 1-billion-M☉ central black hole, and observing guide for M104.
Rigel (Beta Orionis Blue Supergiant)
Coordinates, Hipparcos distance (264 pc), luminosity (120,000 L☉), Rigel BC companion, and observing guide for Rigel in Orion.
Spring Galaxy Season: Ursa Major to Virgo
Spring galaxy observing guide from Ursa Major (M81, M82, Whirlpool M51) across Coma/Virgo to giant elliptical M87, the Sombrero Galaxy (M104), and 3C 273.
Astronomical Epochs (J2000, J2016) & Precession
Why celestial coordinates specify a reference epoch (J2000.0 vs Gaia J2016.0), how axial precession shifts RA/Dec over time, and how ICRS anchors astrometry.
Stellar Spectral Classification (OBAFGKM)
Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.
Scientific Sources & Dataset Provenance
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- IAU Working Group on Star Names (WGSN) (2026 IAU WGSN Bulletin): Mamajek, E., et al. (IAU WGSN) 2016–2026, IAU Catalog of Star Names — International Astronomical Union
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg