Leo/ˈliːoʊ/ is one of theconstellations of thezodiac, betweenCancer the crab to the west andVirgo the maiden to the east. It is located in theNorthern celestial hemisphere. Its name isLatin forlion, and to theancient Greeks represented theNemean Lion killed by the mythical Greek heroHeracles as one of histwelve labors. Its old astronomical symbol is (♌︎). One of the 48 constellations described by the 2nd-century astronomerPtolemy, Leo remains one of the 88 modern constellations today, and one of the most easily recognizable due to its many bright stars and a distinctive shape that is reminiscent of the crouching lion it depicts.

Leo

Constellation
List of stars in Leo
Abbreviation	Leo
Genitive	Leonis
Pronunciation	/ˈliːoʊ/, genitive/liːˈoʊnɪs/
Symbolism	theLion
Right ascension	11h
Declination	+15°
Quadrant	NQ2
Area	947 sq. deg. (12th)
Main stars	9, 15
Bayer/Flamsteed stars	92
Stars withplanets	13
Stars brighter than 3.00m	5
Stars within 10.00 pc (32.62 ly)	5
Brightest star	Regulus (α Leo) (1.35m)
Messier objects	5
Meteor showers	Leonids
Bordering constellations	Ursa Major Leo Minor Lynx (corner) Cancer Hydra Sextans Crater Virgo Coma Berenices
Visible at latitudes between +90° and −65°. Best visible at 21:00 (9 p.m.) during the month ofApril.

Leo contains many bright stars, many of which were individually identified by the ancients. There are nine bright stars that can be easily seen with the naked eye, four of the nine stars are either first or second magnitude which render this constellation especially prominent. Six of the nine stars also form anasterism known as "The Sickle," which to modern observers may resemble a backwards "question mark", The sickle is marked by six stars:Epsilon Leonis,Mu Leonis,Zeta Leonis,Gamma Leonis,Eta Leonis, andAlpha Leonis. The rest of the three stars form an isosceles triangle,Beta Leonis (Denebola) marks the lion's tail and the rest of his body is delineated byDelta Leonis andTheta Leonis.^[1]

Other named stars in Leo includeMu Leonis, Rasalas (an abbreviation of "Al Ras al Asad al Shamaliyy", meaning "The Lion's Head Toward the South"); andTheta Leonis, Chertan.^[2][3]

Leo is also home to a brightvariable star, thered giantR Leonis. It is aMira variable with a minimum magnitude of 10 and normal maximum magnitude of 6; it periodically brightens to magnitude 4.4. R Leonis, 330 light-years from Earth, has a period of 310 days and a diameter of 450solar diameters.^[4]

The starWolf 359 (CN Leonis), one of thenearest stars to Earth at 7.8light-years away, is in Leo. Wolf 359 is ared dwarf of magnitude 13.5; it periodically brightens by one magnitude or less because it is aflare star.^[4]Gliese 436, a faint star in Leo about 33 light-years away from the Sun, is orbited by a transiting Neptune-massextrasolar planet.^[5]

Thecarbon star CW Leo (IRC +10216) is the brightest star in the night sky at the infrared N-band (10 μm wavelength).

The starSDSS J102915+172927 (Caffau's star) is a population II star in thegalactic halo seen in Leo. It is about 13 billion years old, making it one of the oldest stars in the Galaxy. It has the lowestmetallicity of any known star.

Modern astronomers, includingTycho Brahe in 1602, excised a group of stars that once made up the "tuft" of the lion's tail and used them to form the new constellationComa Berenices (Berenice's hair), although there was precedent for that designation among the ancient Greeks and Romans.^[6]

Leo contains many brightgalaxies;Messier 65,Messier 66,Messier 95,Messier 96,Messier 105, andNGC 3628 are the most famous^{[citation needed]}, the first two being part of theLeo Triplet.

TheLeo Ring, a cloud of hydrogen, helium gas, is found in the orbit of two galaxies found within this constellation.

M66 is a spiral galaxy that is part of the Leo Triplet, whose other two members are M65 and NGC 3628. It is at a distance of 37 million light-years and has a somewhat distorted shape due to gravitational interactions with the other members of the Triplet, which are pulling stars away from M66. Eventually, the outermost stars may form a dwarf galaxy orbiting M66.^[7] Both M65 and M66 are visible in large binoculars or small telescopes, but their concentrated nuclei and elongation are only visible in large amateur instruments.^[4]

M95 and M96 are bothspiral galaxies 20 million light-years from Earth. Though they are visible as fuzzy objects in small telescopes, their structure is only visible in larger instruments. M95 is abarred spiral galaxy. M105 is about a degree away from the M95/M96 pair; it is anelliptical galaxy of the 9th magnitude, also about 20 million light-years from Earth.^[4]

NGC 2903 is abarred spiral galaxy discovered byWilliam Herschel in 1784. It is very similar in size and shape to the Milky Way and is located 25 million light-years from Earth. In its core, NGC 2903 has many "hotspots", which have been found to be near regions ofstar formation. The star formation in this region is thought to be due to the presence of the dusty bar, which sends shock waves through its rotation to an area with a diameter of 2,000 light-years. The outskirts of the galaxy have many youngopen clusters.^[7]

Leo is also home to some of the largest structures in the observable universe. Some of the structures found in the constellation are theClowes–Campusano LQG,U1.11,U1.54, and theHuge-LQG, which are alllarge quasar groups; the latter being the second largest structure known^[8] (see alsoNQ2-NQ4 GRB overdensity).

TheLeonids occur in November, peaking on November 14–15, and have aradiant close toGamma Leonis. Its parent body isComet Tempel-Tuttle, which causes significant outbursts every 35 years. The normal peak rate is approximately 10 meteors per hour.^[1]

TheJanuary Leonids are a minor shower that peaks between January 1 and 7.^[9]

Leo was one of the earliest recognized constellations, with archaeological evidence that the Mesopotamians had a similar constellation as early as 4000 BCE.^[10] The Persians called LeoSer orShir; the Turks,Artan; the Syrians,Aryo; the Jews,Arye; the Indians,Simha, all meaning "lion".

Some mythologists believe that in Sumeria, Leo represented the monsterHumbaba, who was killed byGilgamesh.^[11]

In Babylonian astronomy, the constellation was called UR.GU.LA, the "Great Lion"; the bright starRegulus was known as "the star that stands at the Lion's breast." Regulus also had distinctly regal associations, as it was known as the King Star.^[12]

InGreek mythology, Leo was identified as theNemean Lion which was killed byHeracles (Hercules to the Romans) during the first of histwelve labours.^[10][1] The Nemean Lion would take women as hostages to its lair in a cave, luring warriors from nearby towns to save the damsel in distress, to their misfortune.^[13] The Lion was impervious to any weaponry; thus, the warriors' clubs, swords, and spears were rendered useless against it. Realizing that he must defeat the Lion with his bare hands, Hercules slipped into the Lion's cave and engaged it at close quarters.^[13] When the Lion pounced, Hercules caught it in midair, one hand grasping the Lion's forelegs and the other its hind legs, and bent it backwards, breaking its back and freeing the trapped maidens.^[13] Zeus commemorated this labor by placing the Lion in the sky.^[13]

The Roman poetOvid called itHerculeus Leo andViolentus Leo.Bacchi Sidus (star ofBacchus) was another of its titles, the godBacchus always being identified with this animal. However,Manilius called itJovis et Junonis Sidus (Star ofJupiter andJuno).

As of 2002^[update], the Sun appears in the constellation Leo from August 10 to September 16.^[14] Intropical astrology, the Sun is considered to be in the signLeo from July 23 to August 22, and insidereal astrology, from August 16 to September 17.

USS Leonis (AK-128) was aUnited States NavyCrater class cargo ship.

• Leo (Chinese astronomy)

• Star Names: Their Lore and Meaning, by Richard Allen Hinckley, Dover.ISBN 0-486-21079-0
• Ridpath, Ian; Tirion, Wil (2001),Stars and Planets Guide, Princeton University Press,ISBN 0-691-08913-2
• Ian Ridpath and Wil Tirion (2007).Stars and Planets Guide, Collins, London.ISBN 978-0-00-725120-9. Princeton University Press, Princeton.ISBN 978-0-691-13556-4.
• Dictionary of Symbols, by Carl G. Liungman, W. W. Norton & Company.ISBN 0-393-31236-4

• The clickable Leo
• The Warburg Institute Iconographic Database (medieval and early-modern images of Leo)
• Information from StarDate Online
• Ian Ridpath's Star Tales – Leo

  Media related toLeo (constellation) at Wikimedia Commons