Editing Leo (constellation) (section)

==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}}
* [[Regulus]], designated [[Alpha Leonis (star)|Alpha Leonis]], 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]], 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".
* Algieba, [[Gamma Leonis]], 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.
{{endflowlist}}
Other named stars in Leo include [[Mu Leonis]], Rasalas (an abbreviation of "Al Ras al Asad al Shamaliyy", meaning "The Lion's Head Toward the South"); and [[Theta Leonis]], Chertan.<ref>{{cite web|title=Star Names|first=R. H. |last=Allen|url=https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Leo*.html}}</ref><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}}</ref>

{| 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>