Leo constellation

Leo is one of the twelve zodiac constellations, positioned between Cancer to the west and Virgo to the east in the northern celestial hemisphere. Its Latin name means lion, reflecting its association with the Nemean Lion of Greek mythology, a creature vanquished by Heracles during the first of his Twelve Labours. Recognised since antiquity, Leo was catalogued by Ptolemy in the 2nd century CE and remains one of the most familiar modern constellations due to its bright stars and distinctive shape, often interpreted as a crouching lion.

Stellar Features

Leo contains numerous bright stars, many noted since ancient times. The constellation features nine principal stars easily visible to the naked eye, four of which are of first or second magnitude, giving Leo its striking appearance.
A prominent asterism within Leo is the Sickle, a set of six stars—Epsilon Leonis, Mu Leonis, Zeta Leonis, Gamma Leonis, Eta Leonis, and Regulus—that form a pattern resembling a backwards question mark. The remaining stars create an isosceles triangle marked by Beta Leonis (Denebola), Delta Leonis, and Theta Leonis.
Regulus (Alpha Leonis) is the brightest star in Leo, a blue-white main-sequence star of magnitude 1.34 located about 77 light years away. It forms a double system, the secondary component being visible in binoculars. At the opposite end of the constellation lies Denebola (Beta Leonis), a blue-white star of magnitude 2.23 situated some 36 light years from Earth.
Another notable star, Algieba (Gamma Leonis), is a prominent binary with a third optical companion. The pair, both giant stars, have magnitudes of 2.61 and 3.6 and orbit each other over approximately 600 years. The tertiary star, 40 Leonis, is unrelated physically but visible in the same line of sight. Zosma (Delta Leonis) is another bright blue-white star at magnitude 2.58, positioned roughly 58 light years from Earth.
Leo also contains several named stars with traditional designations, including Rasalas (Mu Leonis), meaning “The Lion’s Head Towards the South”, and Chertan (Theta Leonis).
The constellation hosts a number of variable and unusual stars. R Leonis, a Mira variable, fluctuates between magnitude 4.4 and 10 over a 310-day cycle and has a diameter approximately 450 times that of the Sun. Among the nearest stars to Earth is Wolf 359, a faint red dwarf of magnitude 13.5 located roughly 7.8 light years away. Gliese 436, at about 33 light years, is known for its transiting Neptune-mass exoplanet. The carbon star CW Leo (IRC +10216) is particularly bright in infrared wavelengths, while SDSS J102915+172927 (Caffau’s Star) is notable for its extremely low metallicity and great age, estimated at around 13 billion years.
Historically, Tycho Brahe removed a group of stars from Leo’s tail tuft in 1602 to form the separate constellation Coma Berenices, though the attribution to Queen Berenice’s hair dates back to classical antiquity.

Deep-Sky Objects

Leo is rich in galaxies, particularly several bright members of the Messier catalogue. Among the most famous are:

• M65, M66, and NGC 3628, collectively forming the Leo Triplet, a set of interacting galaxies about 37 million light years away. Gravitational forces between them have distorted their shapes and may eventually produce a dwarf galaxy from material drawn off M66.
• M95 and M96, a pair of spiral galaxies approximately 20 million light years distant. M95 is notable for its barred spiral structure.
• M105, an elliptical galaxy near the M95–M96 pair, also located about 20 million light years away.
• NGC 2903, a barred spiral galaxy discovered by William Herschel, similar in form to the Milky Way. It lies 25 million light years from Earth and exhibits concentrated star-forming regions influenced by its central bar.

Leo also contains several extraordinarily large cosmic structures, including the Clowes–Campusano LQG, U1.11, U1.54, and the Huge-LQG, vast quasar groups ranking among the largest formations known in the universe.

Meteor Showers

Two meteor showers originate from Leo:

• The Leonids, peaking around 14–15 November, are produced by debris from Comet Tempel–Tuttle. While the average rate is about ten meteors per hour, the shower generates spectacular storms roughly every 33 years.
• The January Leonids, a minor shower, peak in the first week of January.

Both showers appear to radiate from a region near Gamma Leonis.

Historical and Mythological Background

Leo is one of humanity’s oldest recognised constellations. Evidence suggests that the Mesopotamians identified a similar lion-shaped figure as early as 4000 BCE. Its name, or variants meaning “lion”, appears across ancient cultures including Persian, Turkish, Syrian, Jewish, and Indian traditions. Some interpretations link Leo to the Sumerian monster Humbaba, slain by Gilgamesh.
In Babylonian astronomy, the constellation was called URGULA, the Great Lion, and Regulus was referred to as the King Star.
Greek mythology identifies Leo with the Nemean Lion, a beast impervious to weapons. Heracles confronted it in its cave, ultimately strangling the animal after realising that no weapon could harm it. The triumph was commemorated by Zeus placing the lion among the stars. Roman authors, including Ovid and Manilius, attributed various regal or divine titles to the constellation, linking it to Hercules, Dionysus, Jupiter, and Juno.

Astrological Associations

In astronomy, the Sun appears in Leo roughly from 10 August to 16 September, though this can vary slightly with leap years. In tropical astrology, Leo corresponds to 23 July to 22 August, while sidereal astrology places it between 16 August and 17 September.

Namesakes

The constellation’s name has been used in various contexts, including USS Leonis (AK-128), a United States Navy cargo ship of the Crater class.