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{{for|the painting by Carlo Maria Mariani|The Constellation of Leo}}
{{Short description|Zodiac constellation straddling the celestial equator}}
{{Infobox constellation
| name = Leo
| abbreviation = Leo
| genitive = Leonis
| pronounce = {{IPAc-en|ˈ|l|iː|oʊ}}, genitive {{IPAc-en|l|iː|ˈ|oʊ|n|ᵻ|s}}
|
|
| dec= {{DEC|+15}}
| family = [[Zodiac]]
| quadrant = NQ2
| areatotal = 947
| arearank = 12th
|
| numberbfstars = 92
|
|
| brighteststarname = [[Regulus]] (α Leo)
| starmagnitude = 1.35
| neareststarname = [[Wolf 359]]
| stardistancely = 7.78
| stardistancepc = 2.39
| numbermessierobjects = 5 |
| meteorshowers = [[Leonids]]
| bordering = [[Ursa Major]]<br />[[Leo Minor]]<br />[[Lynx (constellation)|Lynx]] (corner)<br />[[Cancer (constellation)|Cancer]]<br />[[Hydra (constellation)|Hydra]]<br />[[Sextans]]<br />[[Crater (constellation)|Crater]]<br />[[Virgo (constellation)|Virgo]]<br />[[Coma Berenices]]
| latmax = [[North Pole|90]]
| latmin = [[65th parallel south|65]]
| month = April
| notes =
|}}
'''Leo''' {{IPAc-en|ˈ|l|iː|oʊ}} is one of the [[constellation]]s of the [[zodiac]], between [[Cancer (constellation)|Cancer]] the crab to the west and [[Virgo (constellation)|Virgo]] the maiden to the east. It is located in the [[Northern celestial hemisphere]]. Its name is [[Latin]] for [[lion]], and to the [[ancient Greeks]] represented the [[Nemean Lion]] killed by the mythical Greek hero [[Heracles]] as one of his [[Twelve Labours|twelve labors.]] Its old astronomical symbol is [[Image:Leo symbol (fixed width).svg|20px]] (♌︎). One of the 48 constellations described by the 2nd-century astronomer [[Ptolemy]], 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.
==Features==
[[Image:LeoCC.jpg|thumb|The constellation Leo as it can be seen by the naked eye (the bright object in the center of the picture is the planet Jupiter in March 2004).]]
===Stars===
{{See also|List of stars in Leo}}
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 an [[asterism (astronomy)|asterism]] 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]], and [[Regulus|Alpha 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 by [[Delta Leonis]] and [[Theta Leonis]].{{sfn|Ridpath|Tirion|2001|pp=166-167}}
{{flowlist}}
* [[Alpha Leonis (star)|Alpha Leonis]], called [[Regulus]], is a blue-white [[main-sequence]] star of magnitude 1.34, 77.5 light-years from Earth. It is a [[double star]] divisible in binoculars, with a secondary of magnitude 7.7. Its traditional name (Regulus) means "the little king".
* [[Beta Leonis]], also called [[Denebola]], is at the opposite end of the constellation to Regulus. It is a blue-white star of magnitude 2.23, 36 light-years from Earth. The name Denebola means "the lion's tail".
* [[Gamma Leonis]], also called [[Algieba]], is a [[binary star]] with a third optical component; the primary and secondary are divisible in small telescopes and the tertiary is visible in binoculars. The primary is a gold-yellow [[giant star]] of magnitude 2.61 and the secondary is similar but at magnitude 3.6; they have a period of 600 years and are 126 light-years from Earth. The unrelated tertiary, [[40 Leonis]], is a yellow-tinged star of magnitude 4.8. Its traditional name, Algieba, means "the forehead".
* [[Delta Leonis]], called [[Zosma]], is a blue-white star of magnitude 2.58, 58 light-years from Earth.
* [[Mu Leonis]], known as [[Rasalas]], is a red star of magnitude of 3.88, which is bright enough to be seen with the naked eye. This system is 124 light-years from Earth. Rasalas is also known as Alshemali, with both names an abbreviation of "Al Ras al Asad al Shamaliyy", meaning "The Lion's Head Toward the South".
* [[Theta Leonis]], called [[Chertan]], is a white star of magnitude of 3.324 that is visible to the naked eye and forms one of the brighter stars in the constellation and is about 165 light-years from Earth. The name Chertan is derived from the Arabic al-kharātān 'two small ribs', and originally referred to Delta Leonis and Theta Leonis.<ref name="IAU-CSN">{{cite web |url=https://www.iau.org/public/themes/naming_stars/#n4 |title=List of IAU-approved Star Names |access-date=24 January 2022 |archive-date=10 March 2025 |archive-url=https://web.archive.org/web/20250310063743/https://www.iau.org/public/themes/naming_stars/#n4 |url-status=dead }}</ref>
{{endflowlist}}
{| class="wikitable sortable"
|+Brightest Stars of Leo
|-
!Proper Name
!Bayer Designation
!Light Years
!Apparent Magnitude
|-
|Regulus
|[[α Leonis]]
|style="text-align: right;"|79
|style="text-align: right;"|1.35
|-
|Denebola
|[[β Leonis]]
|style="text-align: right;"|36
|style="text-align: right;"|2.14
|-
|Algieba
|[[γ Leonis]]
|style="text-align: right;"|130
|style="text-align: right;"|2.08
|-
|Zosma
|[[δ Leonis]]
|style="text-align: right;"|58
|style="text-align: right;"|2.56
|-
|Algenubi
|[[ε Leonis]]
|style="text-align: right;"|247
|style="text-align: right;"|2.98
|-
|Adhafera
|[[ζ Leonis]]
|style="text-align: right;"|274
|style="text-align: right;"|3.33
|-
|Al Jabhah
|[[η Leonis]]
|style="text-align: right;"|1,270
|style="text-align: right;"|3.49
|-
|Chertan
|[[θ Leonis]]
|style="text-align: right;"|165
|style="text-align: right;"|3.32
|-
|Rasalas
|[[μ Leonis]]
|style="text-align: right;"|124
|style="text-align: right;"|3.88
|}
[[File:Sidney Hall - Urania's Mirror - Leo Major and Leo Minor.jpg|thumb|left|Leo, with Leo Minor above, as depicted in ''[[Urania's Mirror]]'', a set of constellation cards published in London c.1825]]Leo is also home to a bright [[variable star]], the [[red giant]] [[R Leonis]]. It is a [[Mira 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 450 [[solar diameter]]s.{{sfn|Ridpath|Tirion|2001|pp=166-168}}
The star [[Wolf 359]] (CN Leonis), one of the [[List of nearest stars|nearest stars]] to Earth at 7.8 [[light-year]]s away, is in Leo. Wolf 359 is a [[red dwarf]] of magnitude 13.5; it periodically brightens by one magnitude or less because it is a [[flare star]].{{sfn|Ridpath|Tirion|2001|pp=166-168}} [[Gliese 436]], a faint star in Leo about 33 light-years away from the Sun, is orbited by a transiting Neptune-mass [[extrasolar planet]].<ref>{{cite news|url=https://www.theglobeandmail.com/servlet/story/RTGAM.20040831.wplanet20831a/BNStory/specialScienceandHealth |title=Astronomers discover smallest "exoplanets" yet |___location=Toronto |url-status=dead |archive-url=https://web.archive.org/web/20090116080659/http://www.theglobeandmail.com/servlet/story/RTGAM.20040831.wplanet20831a/BNStory/specialScienceandHealth/ |archive-date=January 16, 2009 }}</ref>
The [[carbon star]] CW Leo ([[IRC +10216]]) is the brightest star in the night sky at the infrared N-band (10 μm wavelength).
The star [[SDSS J102915+172927]] (Caffau's star) is a population II star in the [[galactic halo]] seen in Leo. It is about 13 billion years old, making it one of the oldest stars in the Galaxy. It has the lowest [[metallicity]] of any known star.
Modern astronomers, including [[Tycho 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 constellation [[Coma Berenices]] (Berenice's hair), although there was precedent for that designation among the ancient Greeks and Romans.<ref>L. Phil Simpson (Springer 2012) Guidebook to the Constellations: Telescopic Sights, Tales, and Myths, p. 235 ({{ISBN|9781441969415}}).</ref>
===Deep-sky objects===
Leo contains many bright [[galaxy|galaxies]]; [[Messier 65]], [[Messier 66]], [[Messier 95]], [[Messier 96]], [[Messier 105]], and [[NGC 3628]] are the most famous{{citation needed|date=November 2022}}, the first two being part of the [[Leo Triplet]].
The [[Leo Ring]], a cloud of hydrogen, helium gas, is found in the orbit of two galaxies found within this constellation.[[File:Phot-33c-03-fullres.jpg|thumbnail|left|Messier 66]] 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.<ref name="objects">{{cite book |title = 300 Astronomical Objects: A Visual Reference to the Universe |last1 = Wilkins |first1 = Jamie |last2 = Dunn |first2 = Robert |publisher = Firefly Books |___location = Buffalo, New York |date = 2006 |isbn = 978-1-55407-175-3}}</ref> 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.{{sfn|Ridpath|Tirion|2001|pp=166-168}}
[[File: A Horseshoe Einstein Ring from Hubble.JPG|thumb|The notable [[gravitational lens]] known as the [[Cosmic Horseshoe]]]]
M95 and M96 are both [[spiral 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 a [[barred spiral galaxy]]. M105 is about a degree away from the M95/M96 pair; it is an [[elliptical galaxy]] of the 9th magnitude, also about 20 million light-years from Earth.{{sfn|Ridpath|Tirion|2001|pp=166-168}}
[[NGC 2903]] is a [[barred spiral galaxy]] discovered by [[William 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 of [[star 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 young [[open cluster]]s.<ref name=" objects"/>
Leo is also home to some of the largest structures in the observable universe. Some of the structures found in the constellation are the [[Clowes–Campusano LQG]], [[U1.11]], [[U1.54]], and the [[Huge-LQG]], which are all [[large quasar group]]s; the latter being the second largest structure known<ref>{{cite news|date= 11 January 2013|last=Prostak|first=Sergio|title=Universe's Largest Structure Discovered|url=http://www.sci-news.com/astronomy/article00818.html|publisher=scinews.com|access-date=15 January 2013}}</ref> (see also [[NQ2-NQ4 GRB overdensity]]).
===Meteor showers===
The [[Leonids]] occur in November, peaking on November 14–15, and have a [[radiant (meteor shower)|radiant]] close to [[Gamma Leonis]]. Its parent body is [[Comet Tempel-Tuttle]], which causes significant outbursts every 35 years. The normal peak rate is approximately 10 meteors per hour.{{sfn|Ridpath|Tirion|2001|pp=166-167}}
The [[January Leonids]] are a minor shower that peaks between January 1 and 7.<ref>{{cite journal |journal = Sky & Telescope |date = September 2011 |last = Jenniskens |first = Peter |page = 24 |title = Mapping Meteoroid Orbits: New Meteor Showers Discovered}}</ref>
==History and mythology==
[[File:F17.v. Leo -NLW MS 735C.png|thumb|Leo from a western scientific manuscript, c.1000]]
Leo was one of the earliest recognized constellations, with archaeological evidence that the Mesopotamians had a similar constellation as early as 4000 BCE.<ref name="pasachoff"/> The Persians called Leo ''Ser'' or ''Shir''; the Turks, ''Artan''; the Syrians, ''Aryo''; the Jews, ''Arye''; the Indians, ''Simha'', all meaning "lion".
[[File:Hercules and Nemean Lion Stamp.jpg|thumbnail|Cypriot stamp depicting a mosaical image of the encounter between Hercules and Leo, the Nemean Lion]]
Some mythologists believe that in Sumeria, Leo represented the monster [[Humbaba]], who was killed by [[Gilgamesh]].<ref>Tamra Andrews (Oxford University Press 2000) Dictionary of Nature Myths: Legends of the Earth, Sea, and Sky ({{ISBN|9780195136777}}).</ref>
In Babylonian astronomy, the constellation was called UR.GU.LA, the "Great Lion"; the bright star [[Regulus]] 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.<ref>''Babylonian Star-lore'' by Gavin White, Solaria Publications, 2008 page 140, {{ISBN|978-0955903700}}</ref>
In [[Greek mythology]], Leo was identified as the [[Nemean lion|Nemean Lion]] which was killed by [[Heracles]] (Hercules to the Romans) during the first of his [[Labours of Hercules|twelve labours]].<ref name="pasachoff">{{cite book |title=Stars and Planets |last = Pasachoff |first = Jay M. |___location = Boston, Massachusetts |publisher = Houghton Mifflin|isbn=9780395537596 |date = 2006}}</ref>{{sfn|Ridpath|Tirion|2001|pp=166-167}} 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.<ref name=Parker>{{cite book|title=Mythology: Myths, Legends and Fantasies|date=2007|publisher=[[Struik]]|isbn=9781770074538|pages=121–122|editor=Janet Parker|display-editors=etal}}</ref> 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.<ref name=Parker /> 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.<ref name=Parker /> Zeus commemorated this labor by placing the Lion in the sky.<ref name=Parker />
The Roman poet [[Ovid]] called it ''Herculeus Leo'' and ''Violentus Leo''. ''Bacchi Sidus'' (star of [[Dionysus|Bacchus]]) was another of its titles, the god [[Dionysus|Bacchus]] always being identified with this animal. However, [[Marcus Manilius|Manilius]] called it ''Jovis et Junonis Sidus'' (Star of [[Jupiter (mythology)|Jupiter]] and [[Juno (mythology)|Juno]]).
==Astrology==
{{Main|Leo (astrology)}}
{{As of|2002}}, the Sun appears in the constellation Leo from August 10 to September 16.<ref>Jean Meeus, "Zodiacal Constellations", in: ''More Mathematical Astronomy Morsels'' (Richmond: Willmann-Bell Inc., 2002), pp. 327-333. Dates in other years can vary by one day due to the insertion of a [[leap day]].</ref> In [[tropical astrology]], the Sun is considered to be in the sign [[Leo (astrology)|Leo]] from July 23 to August 22, and in [[sidereal astrology]], from August 16 to September 17.
{{Clear}}
==Namesakes==
[[USS Leonis (AK-128)]] was a [[United States Navy]] [[Crater class cargo ship]].
==See also==
* [[Leo (Chinese astronomy)]]
==
{{Reflist}}
* ''Star Names: Their Lore and Meaning'', by Richard Allen Hinckley, Dover. {{ISBN|0-486-21079-0}}
* {{citation |title = Stars and Planets Guide |last1 = Ridpath |first1 = Ian |last2 = Tirion |first2 = Wil |year = 2001 |publisher = 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}}
==External links==
*[http://astrojan.nhely.hu/leo.htm The clickable Leo]
*[https://iconographic.warburg.sas.ac.uk/category/vpc-taxonomy-017063 The Warburg Institute Iconographic Database (medieval and early-modern images of Leo)]
*[https://stardate.org/astro-guide/leo-lion-0 Information from StarDate Online]
*[http://www.ianridpath.com/startales/leo.html Ian Ridpath's Star Tales – Leo]
{{Commons category-inline|Leo (constellation)}}
{{Stars of Leo}}
{{Constellations}}
{{Zodiac}}
{{Portal bar|Astronomy|Stars|Outer space}}
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[[Category:Constellations listed by Ptolemy]]
[[Category:Equatorial constellations]]
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