What kind of star is Spica?
Spica, catalogued as Alpha Virginis (α Vir), appears in the official constellation Virgo. Its apparent visual magnitude is about 0.97–1.04, while its estimated distance is approximately 250 light-years. Astronomers classify the object as Close B-type binary. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
Spica is a double-lined spectroscopic binary: both hot B-type stars imprint moving absorption lines as they orbit their common centre every 4.01 days. The eccentric orbit keeps the components close enough for tidal forces to distort their shapes and influence oscillations, but they do not normally eclipse from Earth's viewing angle. Space photometry and high-resolution spectra identify non-radial pulsation modes in the primary, including behaviour connected to the orbital frequency. Polarimetry has even detected light reflected between the stellar surfaces. These measurements test angular-momentum exchange and internal mixing in massive binaries. Catalogue magnitudes refer to their unresolved combined light, and small brightness changes arise from several interacting effects rather than one simple pulsation clock.
The coordinate pair RA 13h 25m 11.58s, Dec −11° 09′ 40.75″ fixes the object's direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
Spica data at a glance
| Proper name | Spica | Catalogue designation | Alpha Virginis (α Vir) |
|---|---|---|---|
| Constellation | Virgo | Apparent magnitude | about 0.97–1.04 |
| Spectral or system type | Close B-type binary | Estimated distance | approximately 250 light-years |
| Right ascension (J2000) | 13h 25m 11.58s | Declination (J2000) | −11° 09′ 40.75″ |
Values are rounded for an observer-friendly overview. Consult the linked SIMBAD record for component-level identifiers, bibliography, measurement provenance and newer catalogue values.
The name Spica
Latin spīca virginis means “the Virgin’s ear of grain.”
Spica's ear-of-grain imagery became attached to Virgo in Greco-Roman art, while Indian astronomy identifies the star with Chitrā, one of the lunar mansions. Its position close to the ecliptic made conjunctions and occultations valuable to historical positional astronomy. Comparisons involving Spica contributed to ancient recognition that the coordinate framework shifts slowly through precession, although popular accounts often oversimplify which individual observation led Hipparchus to that conclusion.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Spica
Follow the Big Dipper mnemonic: arc to Arcturus, then continue the curve to speed on to Spica. Its blue-white colour contrasts strongly with orange Arcturus.
Visible from nearly all populated latitudes; best in northern spring and southern autumn. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Observation checklist
- Use the Big Dipper handle: arc to Arcturus, then continue the curve to Spica.
- Best evening visibility runs from March through July in the Northern Hemisphere.
- Watch for close Moon passages, but consult local occultation circumstances before expecting disappearance.
- The four-day binary cannot be split visually; spectroscopy is what separates the components' motion.
Interesting facts about Spica
- Spica is a close spectroscopic binary whose components orbit in about four days.
- The two stars are far too close to split in ordinary amateur telescopes.
- Tidal distortion and pulsation produce subtle brightness changes.
- Spica participates in the Spring Triangle and, in some traditions, the Great Diamond.
- The Moon can occult Spica because it lies close to the ecliptic.
Continue from Spica into the night sky
Use the Virgo constellation guide to place this star within its larger pattern. When you are ready to observe, compare dark-sky places, find a nearby observatory, or follow our practical guide to finding a star in the night sky. Symbolically registered names are kept separately in the searchable Star-Register catalogue.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values. Survey panels show photographic sky fields, not the physical surface of the star.