Constellations: Leo 'the Lion' Content from the guide to life, the universe and everything

Constellations: Leo 'the Lion'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
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Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Leo, the constellation.

Name:Leo (Latin: 'lion')
Short form:Leo
Area:947 sq deg
Co-ordinates1:Right Ascension 11h, Declination +15°

The Constellation Leo

The name Leo comes from the Latin form of the Greek leon, which means lion. Measuring 947 square degrees, this northern constellation numbers 12th largest. It is situated between Virgo and Cancer, and also bordered by Leo Minor above its 'head'. The head of the lion and Regulus form a shape like the mirror image of a question mark. In olden times it was sometimes considered to be a constellation in its own right, and bore the name The Sickle2. The Sickle was formed by the stars Regulus, eta, gamma, zeta, mu and epsilon Leonis.

Today a non-constellation group of stars is called an asterism - the Plough (part of Ursa Major - the Great Bear) is one, as is the Summer Triangle.

For amateur astronomers looking for interesting deep-space objects to view, there are five Messier galaxies to track down, and the breathtaking edge-on galaxy NGC 3628 adorns many a professional astronomer's desktop. The constellation itself has some fascinating history; there is a famous meteor shower, and plenty of extrasolar planets are being discovered.


For the ancient Greeks, Leo was the Nemean (or Cleonaean) lion with impenetrable skin that Hercules killed as one of his 12 labours.


Throughout history, the 'king of the beasts', the African lion, symbolised strength and courage. In Egypt the annual Nile flood has always been vital for all life there, and it used to happen while the Sun appeared to pass through the lion constellation. Some historians believe the Sphinx, with its head of the pharaoh and body of a lion, was built to honour it.

The lion appears in heraldry and is usually associated with royalty. The coat of arms of Queen Elizabeth II has seven lions on the shield, a lion supporter (along with the unicorn) and a lion on top, standing on a crown!

The Leonid Meteor Shower

The debris which creates a meteor shower comes from the tail of a comet, as the Earth crosses where the comet passed previously on its own orbit. Imagine a trail of breadcrumbs, or sawdust like that used in hashing. The display is at its best when viewed as soon as possible following the comet's visit; this particular dust which causes the Leonid meteor shower comes from the comet Tempel-Tuttle, which orbits the Sun every 33.25 years. An account was recorded for posterity of the fabulous display in 1799:

During the four hours we observed thousands of huge fireballs, often with a brightness like Jupiter. Long smoke trails were left behind.
- Astronomer Alexander Humbolt observing from Chile.

Who could have guessed that the Leonids would provide an even better show? A very famous date, embedded in the hearts of astronomers everywhere, was when a sprinkling of comet dust was left behind after comet Tempel-Tuttle's passage through the inner Solar System in 1833; the trail hit the Earth's atmosphere on the night of 12 November, 1833. An estimated 200,000 meteors fell between 2am and dawn, creating a legend for the Maricopa Indians of North America, who told the story of 'the night the stars fell' for generations thereafter.

The spectacle repeated in 1866, but the expected showers of 1899 and 1932-3 did not materialise. It was predicted that the 1966 event would be phenomenal, so Patrick Moore, the host of the BBC's long-running astronomy programme The Sky At Night, encouraged his viewers to take part in a 'meteor watch' in the hopes of garnering plenty of data to discuss later. Over ten thousand viewers signed up and received their charts to record the expected celestial fireworks. They waited and waited, but nothing happened. Many stayed up all night in vain, and several of the most irritated rang the BBC to check they'd got the correct night. Patrick was baffled, until the following day when reports came in of a spectacular meteor shower (over 100,000 per hour) taking place over much of the western hemisphere, some 12 hours after the predicted time. In Britain nobody saw a thing; the guinea pigs of the first ever viewer-participation experiment were on the wrong side of the planet.

The Leonids has its virtual point of origin near gamma Leo. You can see them between 14 – 20 November; the maximum rate usually occurs around the 17th. The number of meteors per hour, known as the ZHR (Zenithal Hourly Rate), is very difficult to predict for this shower, but it's usually low: ten or less. The last time comet Tempel-Tuttle shot through was early 1998, but the predicted meteor storm of November 1998 hit the Earth at the wrong time of day for those in the higher northern hemisphere. Astronomers working at the UK's Isaac Newton Telescope on the island of La Palma in the Canaries reported meteors at a rate of 2,000 per hour until dawn broke on Tuesday, 17 November. Lucky them!


The scientific star names are simple to understand (if you know your Greek alphabet). For example: 'alpha' means that it is the brightest star in that constellation. The next brightest is designated 'beta', etc. Combined with the genitive name, this is known as the 'Bayer designation'. Some stars have proper names as well, for example, alpha Leonis is Regulus. Others are known by their catalogue number.

Leo's main star Regulus (alpha Leonis) is one of the four 'Royal Stars' in Mesopotamian culture, the others being Antares (alpha Scorpius), Fomalhaut (alpha Piscis Austrinus 'the Southern Fish') and Aldebaran (the 'Eye of the Bull' in Taurus). Regulus is also called Cor Leonis, which is Latin for 'heart of the lion' or 'the lionheart' (there's that royal connection again!) Of the 25 brightest stars, Regulus is one of very few bright stars close enough to the ecliptic, the path of the planets, to be able to form conjunctions with the planets of our Solar System and with the Moon.

Algieba (gamma Leonis) is a highly regarded binary system. The brighter of the pair is an orange giant and its companion is a yellow giant.

Wolf 359 is, at +13.5m, among the faintest stars in absolute terms ever detected. Discovered in 1918 by German astronomer Max Wolf (1863 - 1932), the star retains his name; the Wolf crater on the Moon is named in his honour as well. Through his career he catalogued 248 discoveries (a record back then) and he also proposed an idea which eventually (after WWI) became the world's first Planetarium.

Star Table

StarDesignationName or
catalogue number
(light years3)
Spectral classification
and/or comments
α Leoalpha LeoRegulus (little king)1.480One of the four 'Royal' stars
β Leobeta LeoDenebola (lion's tail)+2.1436White giant; has a debris disc
γ Leogamma LeoAlgieba (the mane)+2.2/+3.5126Binary star system
δ Leodelta LeoZosma+2.5658White giant
ε Leoepsilon LeoAlgenubi (lion's head)+2.97250Yellow giant
ζ Leozeta LeoAdhafera+3.42260Yellow-white giant
η Leoeta LeoAl Jabhah (forehead)+3.522,100White supergiant
θ Leotheta LeoChertan (the ribs)+3.33170White giant
ι Leoiota LeoTsze Tseang+4.079Yellow-white giant
κ Leokappa LeoAl Minliar al Asad+4.47210Orange giant
λ Leolambda LeoAl Terf+4.32336Orange dwarf
μ Leomu LeoRasalas (lion's head)+3.88133Orange subgiant/has a planet
ν Leonu Leo27 Leonis+5.26526Blue-white dwarf
ξ Leoxi Leo5 Leonis+4.97240Orange giant
ο Leoomicron LeoSubra+3.5135Binary star system
π Leopi Leo29 Leonis+4.68525Red subgiant
ρ Leorho LeoShir+3.845,700Blue-white supergiant
σ Leosigma LeoShishimai+4.05215Blue-white dwarf
τ Leotau Leo84 Leonis+4.95620Yellow subgiant
υ Leoupsilon Leo91 Leonis+4.30180Yellow subgiant
φ Leophi Leo74 Leonis+4.45195White subgiant
χ Leochi Leo63 Leonis+4.6294Yellow-white variable
ψ Leopsi Leo16 Leonis+5.36710Red subgiant
ω Leoomega Leo2 Leonis+5.4112Yellow-white dwarf
CN LeoCN LeonisWolf 359+13.57.7Red dwarf
CW LeoCW LeonisIRC+10216+11 var500Carbon star


Galaxies are categorised by their shape:

  • Spirals have 'arms' which rotate either clockwise (CW) or anti-clockwise (ACW), and they may have a central bar.
  • Elliptical galaxies have no arms and are usually shaped like rugby balls.
  • Lenticular galaxies are a mix between spiral and elliptical.
  • Seyfert galaxies, named after their discoverer, American astronomer Carl Seyfert, have black holes at their core.
Leo has a rich array of different types of galaxies, so they get their own table:

Galaxy Table

Catalogue NumberTypeMagnitudeDistance
(light years)
NGC 3351 (M95)Barred Spiral+10.533m4
NGC 3368 (M96)Clockwise Spiral+10.134m
NGC 3623 (M65)Anti-clockwise Spiral+10.225m
NGC 3627 (M66)ACW Seyfert Spiral+9.634m
NGC 3379 (M105)Elliptical+10.236m
NGC 2903ACW Spiral+9.730m
NGC 3227Seyfert Spiral+11.165m
NGC 3384Barred Lenticular+10.837m
NGC 3489Lenticular+11.139m
NGC 3486ACW Spiral+11.025m
NGC 3521ACW Spiral+9.825m
NGC 3607Elliptical+10.865m
NGC 3628Edge-on Spiral+10.325m
NGC 3593Clockwise Spiral+12.628m
Leo IDwarf Spheroidal+11.2820,000

Extrasolar Planets

There have been several extrasolar planetary systems found in the constellation Leo up to 2007; the first was discovered in 2004. Figures given in the table below are the length of the planet's orbital period around its parent star, which we know of as a year. The mass of the extrasolar planet is compared to that of Jupiter, our Solar System's largest planet; this is known by astronomers as the 'Jovian scale'.

Extrasolar Planets Table

Star name or
catalogue number
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
Gliese 436Gliese 436 b0.0672.642004Smallest discovered (up to 2007)
HD 89307HD 89307 b2.62-3,0002004Circular orbit
HD 88133HD 88133 b0.223.42004Circular orbit
HD 81040HD 81040 b6.81,0002005Eccentric orbit
83 Leonis B83 Leonis B b0.11172005Circular orbit
HD 99109HD 99109 b0.5439.32006Gas giant
HD 100777HD 100777 b1.173842007Eccentric orbit
HD 102272HD 102272 b5.9127.52008Superjovian
HD 102272HD 102272 c2.65202008Superjovian
BD20 2457BD20 2457 b21.423802009Brown dwarf
BD20 2457BD20 2457 c12.476222009Possible brown dwarf
gamma1 Leonisgamma1 Leonis b8.78428.52009Hot superjovian
DP LeonisDP Leonis b6.288,6932009Superjovian
HD 97658HD 97658 b7.5xEarth9.52010Hot super-Earth
HD 95089HD 95089 b1.25072010Gas giant
HD 100655HD 100655 b1.7157.62011Superjovian
HD 96063HD 96063 b0.93612011Gas giant
mu Leonismu Leonis b2.43582014Superjovian/habitable zone
WASP-104WASP-104 b1.31.752014Hot superjovian
WASP-106WASP-106 b1.99.32014Hot superjovian
K2-18K2-18 b8xEarth32.92015Super-Earth/possible ocean/habitable zone
K2-18K2-18 c7.5xEarth8.92017Super-Earth


  • The lion is portrayed as the 'strength' card in a basic Tarot deck.

  • LEO (Lyons Electronic Office) was the world's first business computer.

  • 'Leo the Friendly Lion' is a children's cartoon character created by Bert Felstead.

  • In the science-fiction  Star Trek universe, the first battle between the Federation and the Borg happened at Wolf 359.

  • HRH Princess Anne the Princess Royal celebrates her birthday on 15 August, which, according to Western astrologers, makes her a Leo.

The Name Leo

The name Leo is quite popular, either as a full Christian name or a shortened version of Leonard, Leopold or Leonardo. Queen Victoria liked it so much that she named one of her sons Leopold: he held the title Duke of Albany. Up to 1878, 13 Popes had given themselves that Papal name. His Holiness Pope Leo XIII honoured Corsican-born pharmacist and businessman Angelo Mariani with a Vatican gold medal as a mark of his gratitude for the Vin Mariani wine he had made, which contained the (now banned) ingredient cocaine.

Leo Robin, US songwriter (1900 - 84) wrote 'Diamonds are a Girl's Best Friend' and 'Thanks for the Memory', among others. Leo Blair (named after his paternal grandfather) was the first baby to be born to a serving British Prime Minister for over 150 years. There were a number of Byzantine emperors called Leo. Other notable Leos are the Italian genius inventor, sculptor and artist Leonardo da Vinci, and celebrated Russian writer Leo Tolstoy. And for their many fans, we mustn't forget to mention Leonard Nimoy, Leo Sayer, Leonard Rossiter, Leonardo diCaprio and Leona Lewis!

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (-) for southern ones.2A sickle is a type of blade used for hand-mowing hay or corn.3A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km.4This figure means 33 million light years.

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