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Of all the 88 modern constellations, Leo is a highly recognizable one as it is one among the few constellations that resemble its namesake. It can be easily spotted because the ‘pointer stars’ of the Big Dipper point to it. One of the larger constellations in the northern hemisphere, it is derived from the Latin name meaning ‘lion’. It is one of the zodiac constellations and was first catalogued by the Greek astronomer Ptolemy in the 2nd century, along with all the other constellations of the zodiac. The Persians, Turks, Jewish and Indians all translate it as ‘lion’. The constellation is best visible in the month of April at 9 pm. Let us discuss about Leo further.

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Which stars comprise the constellation?

There are numerous stars in this constellation. Some of the notable ones are:

Regulus (Alpha Leonis): Regulus is the brightest star in Leo and is the 22^nd brightest star in the sky. It has a visual magnitude of about 1.35 and is about 77 light years away. It is basically a four–star system, comprising of two pairs of stars. In the northern hemisphere, it is best seen in the evening during late winter and spring.
Denebola (Beta Leonis): The second brightest star in Leo is Denebola. It is the 61^st brightest star in the sky with a visual magnitude of 2.113. Denebola is about 35.9 light years away from the earth and has about 75% more mass than the sun. The estimated age of the star is believed to be 400 million years.
Algieba (Gamma Leonis): It is basically a double star in the constellation. Algieba comprise of a giant star and a dimmer companion star. The brighter star is around 180 times luminous than the sun with a visual magnitude of about 2.28. The companion star with a visual magnitude of 3.51 is about 50 times brighter than the sun. Both the stars have an orbital period of 500 years. It is easy to observe these stars with a small telescope and it appears as a bright double star with orange, red and greenish yellow components.
Zosma (Delta Leonis): In Leo, Zosma is a rapid rotator with a rotational velocity of 180 km/s. It is basically a white main sequence star, about 58.4 light years away from the earth. Zosma has a visual magnitude of about 2.56 and is slightly hotter and larger than the sun. It is believed that it will evolve into a red giant in about 600 million years.
Chort (Theta Leonis): It is a white main sequence star visible to the naked eye. Chort has a visual magnitude of 3.324 and is about 165 light years away from the solar system. Its estimated age is believed to be 550 million years, which defines that it is comparatively younger than the sun.
Al Minliar (Kappa Leonis): It is basically a binary star with a magnitude of 4.46 and is about 210 light years away from the solar system.
Alterf (Lambda Leonis): Alterf has an apparent magnitude of about 4.32 and is about 336 light years away from the sun.
Subra (Omicron Leonis): It is a double star in the constellation and is about 135 light years away.
Al Jabbah (Eta Leonis): Al Jabbah is a white super giant with a visual magnitude of 3.511 and is about 2,000 light years away from the earth. It usually appears dim to the naked eye but is around 5,600 times more luminous than the sun.
Adhafera (Zeta Leonis): Adhafera is a giant star with a visual magnitude of 3.33 and is about 274 light years away from the solar system. It is about 85 times more luminous than the sun.

The other notable stars in this constellation are Ras Elased Borealis (Mu Leonis), Ras Elased Australis (Epsilon Leonis), Leonis (Rho Leonis), Leonis (Iota Leonis), Leonis (Sigma Leonis), Wolf 359, Gliese 436, CW Leonis (IRC+ 10216) and R Leonis.

Does it contain any deep sky objects or galaxies?

A few among the numerous deep sky objects of the constellation include:

Messier 65 (NGC 3623): In the constellation, Messier 65 is basically an intermediate spiral galaxy. It has a visual magnitude of 10.25 and is around 35 million light years away. In this galaxy, most of the stars are old.
Messier 66 (NGC 3627): It is an intermediate galaxy in Leo. With a visual magnitude of 8.9, Messier 66 is about 36 million light years away. It is a part of the Leo triplet, along with Messier 65 and NGC 3628.
Messier 95 (NGC 3351): It is basically a barred spiral galaxy in the constellation. Messier 95 has a visual magnitude of about 11.4 and is 38 million light years away. Its central region comprises of a ring shaped star–bust region with a diameter that spans for about 2,000 light years.
Messier 96 (NGC 3368): Messier 96 is also an intermediate galaxy in the constellation. It basically has a visual magnitude of 10.1 and is around 31 million light years away.
Messier 105 (NGC 3379): Messier 105 is basically an elliptical galaxy in Leo. It has a visual magnitude of 10.2 and is around 32 million light years away. It is believed that Messier 105 has a massive black hole at its centre.
NGC 3628: It is basically an unbarred spiral galaxy in the constellation and is around 35 million light years away from the solar system. NGC 3628 is believed to have a long tidal tail which spans for about 300,000 light years and also has a broad, obscuring dust band along the outer edge of its spiral arms.

The other notable deep sky objects are the Leo Ring, NGC 3607, NGC 3593, NGC 3384, NGC 3842, NGC 3596, NGC 2903, NGC 3626 and NGC 3357.

What is its position in the galaxy?

It is seen at latitudes between +90⁰ and -65⁰ and is located in the second quadrant of the northern hemisphere.

How much space does it occupy in the sky?

It occupies an area of about 947 square degrees, making it the 12^th largest constellation in the sky.

What is the cultural or mythological significance of Leo?

The constellation Leo is associated with the lion of Nemea in Greek mythology. This lion terrorized the town of Nemea near Corinth and was killed by Heracles as one of his Twelve Labours. Since its skin made it invulnerable, and the arrows bounced off the lion’s skin, Heracles was unable to kill it. Hence, he followed the beast into its cave and choked it to death and later wore it for protection in the battle.

Which are its neighbouring constellations?

Leo is surrounded by constellations like Cancer, Coma Berenices, Crater, Hydra, Leo Minor, Lynx, Sextans, Ursa Major and Virgo.

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