Spica
What is Spica?
Stars· Distance 250 ly · size 7.5× Sun (primary). The blue-white star marking the ear of grain in Virgo's hand. It is two hot stars circling each other about every four days. The ancient astronomer Hipparchus used it to discover that Earth's axis slowly turns.
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Distance and spectral type
Spica is about 250 light-years away, a blue-white main-sequence star (spectral type B1V), in the constellation Leo. Its apparent magnitude is 1, visible to the naked eye.
Stellar figures
| Distance | 250 ly |
|---|---|
| Magnitude | 0.97 — sixteenth brightest |
| Type | B1 + B2 close binary, 4-day period |
| Constellation | Virgo |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Behind the name
Latin "ear of grain" in the maiden's hand. Hipparchus discovered precession using this star.
How Spica's shifting position revealed precession to Hipparchus
In the second century BC the Greek astronomer Hipparchus carefully measured the positions of stars. He compared his position for Spica with a record made by an astronomer about 150 years earlier, and the two did not quite match. The stars seemed to have shifted slowly against the sky's reference points. Hipparchus concluded that this was not an error in measurement, but that the reference points themselves were moving.
Today we know the cause. Earth's spin axis is tilted, and it slowly traces a circle like a wobbling top. This is called precession, and one full circle takes about 26,000 years. Because of it, the points in the sky that mark the start of spring and autumn gradually move, and the star that serves as the pole star changes over time. Spica, a bright star close to the Sun's yearly path, was well placed for measuring such a small shift.
The star in depth
Spica is the brightest star in Virgo. At magnitude 0.97 it is the sixteenth-brightest star in the night sky, 250 light-years away. Its name is Latin for 'ear of grain'. Virgo is drawn as a goddess of grain and harvest, and Spica marks the ear of grain in her hand. It is the only first-magnitude star in Virgo.
Spica looks like one point, but it is two stars, both much heavier and hotter than the Sun. They are only about a third as far apart as Mercury is from the Sun, so they circle each other in four days. At such close range, each pulls the other into an egg shape. As the broad and narrow sides of these stretched stars turn toward us in turn, Spica's brightness changes slightly every four days.
Heavy stars live short lives. Spica's two stars are only about twelve million years old, and the heavier one is expected to explode as a supernova one day. Its surface also trembles slightly every few hours. In 2026 a study reported a third star orbiting a little farther out from the pair.
Look for Spica in the southern evening sky from April to June. Follow the curved handle of the Big Dipper to orange Arcturus, then keep going along the same curve to reach Spica. This curve is called the Spring Arc. With no bright stars nearby, Spica is easy to recognise as a lone blue-white star. In the Sky view, choose a May night and select Virgo to find it.
Frequently asked
- How far is Spica from Earth?
- The distance of Spica is 250 ly.
- How bright is Spica (apparent magnitude)?
- The magnitude of Spica is 0.97 — sixteenth brightest.
- What kind of object is Spica?
- Spica is a B1 + B2 close binary, 4-day period.
- Which constellation is Spica in?
- Spica lies in the constellation Leo.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.