Regulus A [Alpha Leonis] is the brightest star in the constellation Leo and one of the brightest stars in the night sky, lying approximately 79 light years from Earth. It is a binary star consisting of a blue-white main sequence star of spectral type B7V, which is orbited by a star of at least 0.3 solar masses, which is probably a white dwarf. The two stars take approximately 40 days to complete an
orbit around their common centre of mass. Located farther away is the pair Regulus B and Regulus C, which are dim main-sequence stars.
The Regulus System as a whole is the twenty-first brightest system in the night sky with an apparent magnitude of +1.35. The light output is dominated by Regulus A. Regulus B, if
seen in isolation, would be a binocular object of magnitude +8.1, and
its companion, Regulus C, the faintest of the three stars that has been
directly observed, would require a substantial telescope to be seen, at
magnitude +13.5. Regulus A is itself a spectroscopic binary: the
secondary star has not yet been directly observed as it is much fainter
than the primary.
Rēgulus is Latin for “prince” or “little king”. The Greek variant Basiliscus is also used. It is known as Qalb al-Asad, from the Arabic قلب الأسد, meaning “the heart of the lion”. This phrase is sometimes approximated as Kabelaced and translates into Latin as Cor Leōnis. It is known in Chinese as 轩辕十四, the Fourteenth Star of Xuanyuan, “the Yellow Emperor”. In Hindu astronomy, Regulus corresponds to the Nakshatra Magha - “the bountiful”.