Leo Constellation Facts, History & Mythology

Leo is one of the most ancient and recognizable of all the constellations. It was recognized by Ptolemy in the 2nd century and was included in his list of 48 constellations. It remains one of the 88 modern constellations and is typically considered the 5th constellation of the zodiac.

Part of what makes Leo such a well-known constellation is how easily recognizable it is. Leo is one of the constellations that actually looks like what it is meant to resemble. The constellation has a clear outline of a crouching lion. Leo also has a distinct sickle-like shape which many observers see as a backwards question mark. This asterism also helps make it quite easy to point out. The Sickle, or question mark asterism, forms the lion’s mane and shoulders.

You can find where Leo is located by following the other constellations in the zodiac. Leo lies between the crab constellation Cancer to the west, and the constellation Virgo the maiden to the east. Both Cancer and Virgo are relatively obscure constellations, and not that easy to point out. If you want to locate Leo more easily, find the popular constellations Orion and Taurus. Taurus also lies on the zodiac, and you can follow the general path of the constellation until you find the distinct sickle asterism.

History and Mythology of The Constellation Leo

Greek and Roman Mythology

The ancient astronomer Ptolemy included Leo is his listing of constellations, but he wasn’t the first or only to recognize the lion. There is evidence that the Mesopotamians took note of Leo as early as 4000 BCE. Other ancient people’s also have records of the constellation: ancient Persians, Turks, Syrians, Jews, Indians and Sinha all had names for Leo which translate to ‘lion’.

Leo also features prominently in ancient mythologies. The constellation Leo, to the ancient Greeks and Romans, represented the Nemean Lion which the hero Hercules kills in the first of his twelve labors. In this myth, the lion would trap women in his cave as a way to lure warriors into his lair. The men would rush into the lair to try to save the damsel taken hostage, but upon getting close, the woman would turn into a lion and devour the helpless warrior.

Hercules meets a boy who tells the hero that his town will sacrifice a lion to Zeus if Hercules can kill the Nemean Lion and return alive. However, if Hercules fails, the boy will sacrifice himself. In an alternative telling, Hercules meets a shepherd who has lost his son to the lion, and who vows that he will sacrifice a ram if Hercules can defeat the beast.

In his quest to conquer the lion, Hercules soon realizes that the lion’s golden fur is impenetrable. Hercules waits for the lion to return to his cave, and there he stuns the beast with his club and uses his superhuman strength to strangle the lion to death with nothing but his bare hands. Some accounts mention that Hercules doesn’t win unscathed; losing a finger to the lion during the epic struggle.

Hercules then tries to skin it with a knife from his belt, but his efforts are lost since the fur is impervious to all weapons. The goddess Athena is impressed with Hercules’ feat, and tells him to use one of the lion’s own claws.

Zeus then commemorates the hero’s accomplishment by placing the lion in the sky as the constellation Leo. There is also a Greek stamp showing the encounter between Hercules and Leo.

Babylonian Astronomy and Sumerian Mythology

The ancient Babylonian astronomers called the constellation UR.GU.LA, which translates to the “Great Lion”. Regulus, the brightest star Leo, was recognized as “the star that stands at the Lion’s breast.” The Babylonians also called Regulus the “King Star”.

Some mythologists have pointed out that Leo may be the beast Humbaba, of Mesopotamian lore. The monster was said to have the face of a lion and guarded a forest, though he terrorized the humans nearby. The beast was eventually killed by the Sumerian hero Gilgamesh.

Stars In The Constellation Leo

Another reason why Leo is so easily recognized – and has been since antiquity – is that the constellation houses several bright stars. Most of the bright stars we see in Leo today were identified by ancient astronomers. Four of the stars in Leo are second magnitude stars or brighter.

  • The brightest star in the constellation Leo is Regulus, with a magnitude of 1.34. The star has the designation Alpha Leonis, setting it apart as the brightest. Regulus appears as a blue-white star located over 77 light years away from Earth. Overall, Regulus is one of the brightest stars as seen from Earth; usually the 21st brightest star.

Regulus looks like a single white star to the naked eye. Through binoculars, you can see that Regulus is a double star. The secondary star is a dimmer magnitude of 7.7, and is most likely a white dwarf star. Professional observations reveal that Regulus is actually a quadruple star system composed of four stars grouped in two pairs.

Regulus is one of the six stars that make up The Sickle asterism which forms Leo’s mane and shoulders.

  • Denebola, designated Eat Leonis, marks the bright tip of the lion’s tail, and lies opposite to Regulus. The name Denebola is an Arabic phrase meaning “the lion’s tail”. The star shines at magnitude 2.23 and is situated over 35 light-years from Earth. Denebola is a relatively young main sequence star. The star forms part of the asterism the Spring Triangle, along with stars Spica and Arcturus.
  • Algieba, or Gamma Leonis, is a binary star 126 light years from Earth. The binary system also has a third optical component (the third star only looks like it is part of the system when seen with the naked eye). Two of the stars in the system are divisible with small telescopes, while the third star is divisible using binoculars. The primary is a giant star of magnitude 2.61, while the secondary star has a magnitude of 3.6. Algieba, means “the forehead” in Arabic.
  • Zeta Leonis, also called Adhafera, looks like it belongs to a system of 3 stars as they appear very close together and account for how bright it looks with the naked eye. Actually, none of the three stars are physically related. The brightest of the three is a white giant star of magnitude 3.65. It lies 260 light-years from Earth.
  • One of the closest stars to Earth lies in the constellation Leo. Wolf 359 (CN Leonis) is only about 7.8 light-years away. The star is a red dwarf with a magnitude of 13.5. Wolf 359 is a flare star which periodically brightens by a magnitude or less.

Other stars in the constellation Leo include:

  • Delta Leonis, also called Zosma, a magnitude 2.58 which is found 58 light-years from Earth.
  • Epsilon Leonis, a magnitude 3.0 lying 251 light-years away.
  • Iota Leonis, a double star system 79 light-years from Earth. The system is divisible in medium aperture telescopes. The primary is over magnitude 4 and the secondary shines at magnitude 6.7.
  • Tau Leonis is a double star with both stars visible in binoculars.
  • Gliese 436 is a faint star in Leo with a Neptune-mass exo-planet in its orbit.
  • CW Leo is the star which shines brightest in infrared.
  • Caffau’s is a star in Leo, and it is one of the oldest that we know. The star is about 13 billion years old.
  • Mu Leonis.
  • Rasalas (meaning “The Lion’s Head Toward the South”).
  • Theta Leonis.
  • R Leonis is a red giant variable star in Leo.
  • and Chertan or Coxa (forming the hip of the lion).

Galaxies and Other Deep Sky Objects in Leo

Along with its many bright stars, Leo also contains a number of bright galaxies and some other interesting deep sky objects.

  • Messier 66, or M66, is a spiral galaxy in the constellation. The galaxy belongs to the Leo Triplet, a small group of galaxies about 35 million light-years, together with the galaxies M65 and NGC 3628. M66 has a slightly distorted shape because of its interactions with the two other members of the Leo Triplet. The galaxy is visible in both larger binoculars and backyard telescopes, making it a great deep sky target for amateurs to observe. That said, the galaxy’s elongated shape is only visible in professional instruments. M65 can also be viewed in small telescopes, but again, will not reveal much detail.
  • Astronomer William Herschel discovered the galaxy NGC 2903 in 1784. The galaxy lies 25 million light years from Earth and closely resembles the Milky way in shape and size. Astronomers have observed hotspots at the galaxies center which lie close to star-forming regions. Astronomers have also found that the edges of the galaxy house a number of young open star clusters.
  • Two other Messier objects in Leo that can be viewed with small telescopes are M95 and M96. These are spiral galaxies which both lie approximately 20 million light-years away. They are not very well resolved in small instruments, showing up as fuzzy patches in the sky. You will need a much larger telescope to be able to these galaxies’ spiral structures. M105, an elliptical galaxy of around magnitude 9, lies only a degree away from the two spiral galaxies.
  • Leo hosts some of the biggest cosmological structures we know of in the universe, including large quasar groups. The Huge Large Quasar Group (HLQ Group) in Leo measures about 4 billion light-years across and is currently considered the second biggest structure in the universe.

Meteor Showers in The Constellation Leo

The Leonids meteor shower radiates from the constellation Leo. The meteor shower is typically average and unspectacular. The Leonids meteor shower happens in November and is set to peak around November 17th – 18th in 2019. The radiant of the showers is close to the star Gamma Leonids.

The Leonids are caused by Comet Tempel-Tuttle. Though the Leonids are usually nothing to write home about, the comet does some sometimes flare up, causing a significant increase in the rate of meteors we see during the Leonids showers. The normal peak rate for the Leonids is approximately 10 meteors per hour.

There is also a lesser shower radiating from Leo early in the year. The January Leonids reach its peak around January 1st and 7th but has a very low rate of meteors even at its maximum.