Leo
What is Leo?
Constellations· Spring evenings (N) · the backwards question mark (Sickle). The signature constellation of spring. A backwards question mark called the Sickle draws the lion's head and mane, with bright Regulus as its heart. The November Leonid meteors appear to fly out from here.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Regulus | 1.4 |
| Algieba | 2.0 |
| Denebola | 2.1 |
The 3 brightest of the 10 stars used in the figure (11 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | spring |
|---|---|
| Brightest star | Regulus (1.4) |
| Shape | the backwards-question-mark Sickle |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Once every 16 hours — Regulus, the lion's spinning heart
Regulus turns once in about 16 hours, astonishingly fast compared with roughly 25 days for the Sun. The spin makes its equator bulge outward, so its equatorial radius is about 30 percent larger than its polar radius. Spinning only a little faster would bring it close to the point where the star would start to fly apart.
A star flattened like this is hotter and brighter at its poles than at its equator, so its measured brightness and colour depend on the angle from which it is seen. Scientists look to a companion to explain the fast spin. A small star, apparently on its way to becoming a white dwarf, circles Regulus every 40 days or so. The leading explanation is that long ago it passed material to Regulus and handed over its spin along with it.
The constellation in depth
When Leo climbs into the evening sky, spring has arrived. A backwards question mark of stars called the Sickle draws the lion's head and mane, and first-magnitude Regulus, the dot beneath it, is the heart. A triangle of stars running east from the Sickle forms the body and tail, so the whole figure really does look like a resting lion.
Regulus means little king in Latin. It sits almost exactly on the ecliptic, the path the Sun follows through the year. The Moon and planets move along nearly the same path, so they often pass close to Regulus, and now and then the Moon slides in front of it and hides it for a while.
Each November the Leonid meteor shower arrives, made of debris from Comet Tempel–Tuttle burning up in Earth's air. About every 33 years it can turn into a storm; in 1833 tens of thousands of meteors fell in an hour. Forecasts call for stronger activity again in 2033–2034, though most suggest that a storm on the scale of 1833 is unlikely for many decades.
Frequently asked
- When can I see Leo?
- Leo is best seen in spring.
- What is the brightest star in Leo?
- The brightest star in Leo is Regulus, at magnitude 1.4.
- In one line, what is Leo?
- Constellations — The signature constellation of spring.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.