The Lion · pronounced LEE-oh. Leo is a large zodiac constellation whose bright Sickle asterism resembles a backward question mark. Regulus marks the lion's heart, while Denebola marks its tail. The pattern is prominent in Northern Hemisphere spring skies and also contains the Leo Triplet and several Messier galaxies.
About Leo
Leo is one of the 88 constellations recognized by the International Astronomical Union. Its standard three-letter abbreviation is Leo, and astronomers use the genitive form Leonis when naming stars associated with it. The constellation's reference position lies around right ascension 10.6 hours and declination +15 degrees.
Its location places it in the celestial equator. For a typical mid-latitude observer, this part of the celestial sphere is especially well placed during winter evenings. Exact visibility depends on latitude, local horizon, date and time.
History and mythology of Leo
A lion across ancient skies
Leo's identification with a lion predates classical Greece. Lion imagery was associated with this part of the sky in Mesopotamian traditions, and related interpretations appeared in Persia, Syria and Egypt. These traditions were not identical stories, but the recurring animal image is unusually persistent.
Greek and Roman tradition
In the best-known Greek account, Leo represents the Nemean Lion, whose hide could not be pierced by weapons. Heracles defeated it as the first of his twelve labours. Ptolemy included Leo among the 48 constellations in the Almagest; it later became one of the 88 regions standardized for modern astronomy.
Astronomy, not astrology
Leo is both an official IAU constellation and one of the constellations crossed by the ecliptic. The astronomical constellation is an irregular region with real sky boundaries. The astrological sign called Leo is a conventional 30-degree segment of the zodiac, so the two should not be treated as the same area.
How to find Leo
- Start with the Big Dipper. The two stars on the outer edge of its bowl point generally toward Leo when followed away from Polaris.
- Look for the Sickle: six stars forming a backward question mark. Regulus is the bright star at the bottom of this curve.
- From Regulus, trace east through the lion's body to a triangle of stars. Denebola, whose name refers to the lion's tail, is the eastern point.
- From mid-northern latitudes, Leo is best placed during March, April and May evenings. Face generally south after darkness falls.
Bright stars in Leo
Regulus
Alpha Leonis- Magnitude
- 1.35
- Distance
- about 79 light-years
A blue-white multiple-star system close to the ecliptic. It anchors the base of the Sickle and traditionally marks the lion's heart.
Denebola
Beta Leonis- Magnitude
- 2.14
- Distance
- about 36 light-years
A white main-sequence star at the lion's tail and one vertex of the Spring Triangle asterism.
Algieba
Gamma Leonis- Magnitude
- 2.0 combined
- Distance
- about 130 light-years
A striking golden-orange binary in the Sickle. A modest telescope can resolve its two giant stars under good conditions.
Zosma
Delta Leonis- Magnitude
- 2.56
- Distance
- about 58 light-years
A white star marking the lion's hip and helping form the prominent triangle toward Leo's eastern side.
Deep-sky objects in Leo
M65, M66 and NGC 3628
Three interacting spiral galaxies sharing one telescopic field. M65 and M66 are Messier objects; edge-on NGC 3628 shows a conspicuous dust lane in photographs.
M95
A face-on barred spiral roughly 33 million light-years away, with a bright central ring where star formation is active.
M96
The brightest major member of the M96 Group, appearing as an asymmetric spiral because of its orientation and gravitational environment.
M105
A large elliptical member of the M96 Group, commonly viewed with nearby NGC 3384 and NGC 3389.
Meteor showers associated with Leo
Leonids
Peak: around 17–18 NovemberA fast meteor shower produced by debris from comet 55P/Tempel–Tuttle. Most years are modest, but roughly 33-year cycles can produce exceptional meteor storms.
Interesting facts about Leo
- Leo means “The Lion” and is pronounced LEE-oh.
- Regulus is a notable star in Leo, listed here at magnitude 1.35.
- M65, M66 and NGC 3628 is a leo triplet found within the constellation's boundaries.
- Leonids meteors appear to radiate from this part of the sky.
Leo lies on the astronomical path of the Sun through the IAU sky regions. The Sun crosses 13 official constellations, including Ophiuchus; this is different from the equal 12-sign structure used by Western tropical astrology.