Spica lies only 2.06 degrees from the ecliptic, which means that it can be occulted by the Moon and, more rarely, by planets. Spica is the only navigational star in the constellation Virgo. Navigational stars play a special role in the field of celestial navigation because they are some of the brightest and most identifiable stars in the sky. Spica is one of the 58 bright stars selected for navigation. Even though the stars reflect very little of the incident light, the reflected light is highly polarized. A study published in 2019 yielded geometric albedos of 3.61 percent and 1.36 percent for Spica A and Spica B. The two stars were the first to have their geometric albedo (reflectivity) measured. Most of the polarimetric signal comes from the reflection of the primary star’s light off the companion and vice versa. The stars’ gravitational interaction over time may reduce the eccentricity of their orbit and lead to more synchronous rotation.Ī study published in 2016 revealed that Spica is a polarimetric variable. This is known as the Struve-Sahade effect.īoth stars rotate more rapidly than their orbital period, and the lack of synchronization, coupled with the highly elliptical orbit, may indicate that the star system is still young. The strength of the star’s spectral lines varies during the orbital motion, becoming weaker as the star moves away from the observer, possibly as a result of a strong stellar wind from Spica A scattering its light. Its projected rotational velocity is 58.8 km/s. It has a luminosity 2,254 times that of the Sun. It is a main sequence star of the spectral type B2V. Other well-known stars in this class include Hadar (Beta Centauri), Mimosa (Beta Crucis), Imai (Delta Crucis), Mirzam (Beta Canis Majoris), Algenib (Gamma Pegasi), and Shaula (Lambda Scorpii).Īlpha Virginis B is cooler, smaller and less massive, with a temperature of 20,900 K, a radius 3.74 times that of the Sun and a mass of 7.21 solar masses. It varies in brightness with a period of 0.1738 days. The primary component is classified as a Beta Cephei variable, a star showing small, rapid fluctuations in brightness as a result of pulsations of its outer layers. It is one of the nearest stars to the solar system that is massive enough to be a Type II supernova candidate. The star is a fast spinner, with a projected rotational velocity of 165.3 km/s. With an effective temperature of about 25,300 K, it is 20,512 times more luminous than the Sun, but a lot of its energy output is in the invisible ultraviolet. It has an estimated mass 11.43 times that of the Sun and a radius 7.47 times solar. The primary star in the system has the stellar classification B1III-IV, indicating a blue giant or subgiant star. Its brightness varies by only 0.03 magnitudes and the variations cannot be noticed visually. Spica is the brightest star of this type in the sky. Rotating ellipsoidal variable stars typically show variations in brightness of up to 0.1 magnitudes and their periods correspond to their orbital motion. Their brightness varies because they are ellipsoidal in shape and their apparent diameters change as they orbit, not as a result of any physical changes to the stars themselves. The stars do not eclipse each other during their orbit, but show changes in brightness as a result of the changes in what the observer sees of the stars due to their rotation. Spica is classified as a rotating ellipsoidal variable, a spectroscopic binary star whose two components are so close together that their shape is distorted by their gravitational interaction. Spica is a double-lined spectroscopic binary (SB2), which means that spectral lines of both components are visible and the lines are sometimes double and sometimes single. The stars are too close together – they are separated by only 0.12 astronomical units – to be resolved in a telescope and can only be detected as a pair through their spectral lines. Spica is a spectroscopic binary star consisting of two stars in a close orbit with an orbital period of 4.0145 days. It is only slightly fainter than Altair in the constellation Aquila, Acrux in Crux, Aldebaran in Taurus and Antares in Scorpius, and it just outshines Pollux in Gemini and Fomalhaut in Piscis Austrinus. With an apparent magnitude of 0.97, it is the brightest star in Virgo and the 16th brightest star in the sky. Spica, Alpha Virginis (α Vir), is a blue-white spectroscopic binary star located at a distance of 250 light years from Earth in the constellation Virgo.
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