Regulus (Alpha Leonis)
Regulus (Alpha Leonis) is a star in the constellation Leo, magnitude 1.4.
The little king at the Lion’s heart — a star spinning so fast it is close to flying apart.
Regulus spins once every 15.9 hours; the Sun takes about 25 days. Its equator whirls round at about 320 km/s — 96.5% of the speed at which it would start to fly apart. The spin squashes it into a flattened shape, and its poles shine hotter and, area for area, five times brighter than its waist.
It is a multiple star of at least four. The bright one has a dim partner, probably a white dwarf, that circles it every 40 days, and a wider pair of small orange and red stars travels with them. That white dwarf hints at a strange history: the main star may have grown by taking gas from its companion.
Its name is Latin for ‘little king’, and royalty follows it through history. The Babylonians called it Sharru, ‘the King’, and in Persia it was one of the four royal stars. Its Arabic name, Qalb al-Asad, means ‘the heart of the lion’.
Regulus (Alpha Leonis) is 79 light-years away: the light we see from it set off in 1947, 10 years before Sputnik became the first artificial satellite.
Did you know?
- Closest to the Sun’s path. Regulus lies less than half a degree from the ecliptic — the closest of all the bright stars — so the Moon often covers it. Venus last passed in front of it on 7 July 1959 and will again on 1 October 2044.
- Einstein in an asteroid’s shadow. When the asteroid 166 Rhodope passed in front of Regulus in 2005, observers in Italy filmed it. The tiny bending of the star’s light matched the predictions of general relativity.
A bright blue-white star at the base of the Sickle, the backwards question mark that forms Leo’s head and mane. A small telescope shows a faint companion well off to one side.
When and where to see it
It is best placed in the evening sky around March, when it crosses the meridian at about 10 pm local time (around midnight in February). It can be seen from everywhere north of 78°S and never sets north of 78°N.
At its highest it stands 52° up from 50°N, 67° up from 35°N, 78° up from the equator, 43° up from 35°S.
Facts
- Type
- Star
- Constellation
- Leo
- Designations
- Alpha Leonis, α Leo, 32 Leo, HR 3982, HD 87901, HIP 49669
- Magnitude
- 1.4
- Position
- RA 10h 8.4m, Dec +11° 58′ (J2000)
- Spectral type
- B8IVn
- Colour
- blue-white (B−V -0.16)
- Distance
- 79 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Regulus (Alpha Leonis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.