Leo

Leo is one of the 12 zodiac constellations and one of the few that genuinely looks like its name. The bright stars of Leo really do form the rough outline of a crouching lion, with a triangle for the back legs and tail, and a curved pattern called the Sickle (or a "backwards question mark") for the head and chest. Leo is best seen in the spring evenings of the Northern Hemisphere (autumn evenings in the South).

• Best seen fromBoth hemispheresSits near the celestial equator
• Best viewing timeSpring evenings(Northern hemisphere)
• Brightest starRegulus"Little King", 79 light years away
• Zodiac signJuly 23 to August 22The Sun appears in Leo (astronomically Aug 10 to Sep 16)
• Famous asterismThe SickleReverse question mark forming the lion's head
• Famous galaxiesThe Leo TripletThree spirals visible together in telescopes

The Sickle: a backwards question mark

The most distinctive part of Leo is the Sickle, an asterism shaped like a backwards question mark or an old-fashioned farming sickle. The Sickle forms the lion's mane, head and chest. At the bottom point of the Sickle sits Regulus, the brightest star in the constellation. From the back end of the Sickle the lion's body stretches off east, ending in a triangle of stars that makes up the haunches and tail. The brightest star in that triangle is Denebola, which actually means "the lion's tail" in Arabic.

How to find Leo

The easiest way to find Leo is to use the Big Dipper as a pointer. The two stars at the bottom of the Big Dipper's bowl (not the famous Merak and Dubhe that point to Polaris, but the other two: Megrez and Phecda) point downward roughly towards Leo. From a clear dark site, look south on a spring evening and you cannot really miss Regulus, which shines brightly at the bottom of the Sickle.

Leo is best seen between approximately February and June from the Northern Hemisphere, and between approximately August and December from the Southern. In the southern view, the lion appears to be standing on its head.

Regulus, the "Little King"

Regulus is the 21st brightest star in the night sky. Its name comes from Latin and means "little king": almost every ancient culture that named this star treated it as royalty. In ancient Persia it was one of the four "royal stars of the sky" that watched over the four points of the compass. In Babylonian astronomy it was the King Star.

Regulus is actually a four-star system about 79 light years from Earth. The main star is a hot blue-white giant spinning so fast that it has flattened itself into an egg shape: its equator bulges outward at over 1.3 million kilometres per hour. It is around 4 times the mass of the Sun and 350 times brighter. Three smaller, fainter companion stars orbit it.

The myth of the Nemean Lion

In Greek mythology, the constellation Leo was the Nemean Lion, a monstrous beast that lived in the valley of Nemea and could not be hurt by any normal weapon. Its golden fur was harder than any sword. The lion terrorised the local people until the hero Hercules was sent to kill it as the first of his famous Twelve Labours.

Hercules quickly discovered that his arrows just bounced off the lion's skin. So he wrestled it bare-handed in its cave and strangled it. Afterwards, he used the lion's own claws (the only thing sharp enough) to skin it, and wore the impenetrable hide as armour for the rest of his life. The gods placed the lion in the sky as the constellation Leo, where it has stayed for over 2,000 years.

Fact Hidden inside Leo are three famous spiral galaxies called the Leo Triplet (also called the M66 Group). These three spirals, each tens of millions of light years away, can be seen close together in the same telescope view. They are gravitationally bound to each other and are slowly pulling each other apart as they orbit, dragging long tails of stars and gas through space.

Leo and the zodiac

Leo is one of the 12 constellations that lie along the ecliptic, the path the Sun takes through the sky over the course of a year. That makes Leo a zodiac constellation. The Sun actually passes through Leo each year between approximately 10 August and 16 September. (Astrological "Leo" dates of 23 July to 22 August are based on a 2,000-year-old calendar and have drifted out of sync with the real positions of the stars due to precession.)

Did you know? Every November, Earth passes through a stream of dust left behind by the comet Tempel-Tuttle. The dust burns up in our atmosphere and produces a meteor shower called the Leonids, which appear to come from the head of the lion (the Sickle). Most years the Leonids are modest, but every 33 years (when comet Tempel-Tuttle swings back close) the shower can produce thousands of meteors an hour, a real "meteor storm".

Deeper dive: the difference between zodiac astronomy and astrology

The zodiac is both an astronomical thing (12 real constellations along the Sun's path) and an astrological thing (12 "sun signs" used to predict personality and the future). It is important to remember that the two are very different.

Astronomy is the scientific study of stars, planets and space using observation and physics. Astrology is the much older belief that the positions of stars and planets at the moment of your birth influence your personality and life. Scientific studies have looked at astrological predictions many times and found that they do not work better than random chance. The 12 zodiac dates used by astrologers are also based on the positions of the stars about 2,000 years ago. Because of precession (the slow wobble of the Earth's axis), the Sun is now in a different constellation from the "sign" on a typical astrology chart by about a month. So someone whose star sign is "Leo" actually has the Sun in Cancer when they are born.

There is also a 13th zodiac constellation that astrologers usually leave out: Ophiuchus. The Sun spends about 18 days a year passing through Ophiuchus (roughly 30 November to 17 December), which makes the astronomical zodiac genuinely 13 constellations, not 12. The astronomy and the astrology really do not match up.

For more zodiac constellations, see the Zodiac. Or jump back to Orion and Ursa Major.