Spring Constellation Spotlight: Leo

May 28, 2025

Recognized since ancient times, Leo is one of the most prominent constellations in the Northern Hemisphere's Spring night sky. Its distinctive shape—resembling a backward question mark, a sickle, or a crouching lion—makes it easily identifiable. Leo holds historical and mythological significance as one of the twelve zodiac constellations. It ranks as the 12th-largest among the 88 official constellations and is home to numerous notable galaxies, making it a favorite among astroimagers. Let's dive into Leo and explore why this constellation captivates backyard astronomers.

 

Mythology

Leo is Latin for lion. The Greek astronomer Ptolemy cataloged Leo in the second century AD, and it has appeared in star maps across cultures for millennia. The ancient Babylonians associated Leo with a lion-shaped deity. Egyptian astronomers linked its position in the sky to the annual flooding of the Nile—an event vital to agriculture.

In Greek mythology, Leo represents the Nemean Lion—a fearsome beast that terrorized the countryside until Heracles (Hercules in Roman mythology) faced it during his twelve labors. The lion’s hide was impervious to weapons, forcing Heracles to wrestle it barehanded and ultimately strangle it to death. Afterward, he used the lion’s own claws to skin it and wore the pelt as armor. Impressed by the lion’s power and Heracles’ triumph, Zeus placed the creature among the stars as the constellation Leo.

 

How to Find Leo

Leo is one of the easiest constellations to find in the springtime night sky in the Northern Hemisphere. Here's how to locate it:

  1. Find the Big Dipper.
    This familiar asterism rides high in the Spring sky. Focus on the two stars forming the side of the bowl opposite the handle—Megrez (top) and Phecda (bottom).
  2. Draw an imaginary line.
    Extend a line downward from Megrez through Phecda until it points to Regulus, the brightest star in Leo and the lion’s heart.
  3. Locate the Sickle.
    Just above Regulus, look for a pattern of stars shaped like a backward question mark. This is the Sickle, representing Leo’s head and mane.
  4. Find the triangle.
    To the left of the Sickle, a triangle of stars outlines Leo’s hindquarters and tail. The furthest and brightest of these stars is Denebola.
    Leo is best viewed in April, when it sits high in the night sky around 9 p.m., making it easy to spot. This prominent constellation is visible from most locations on Earth and is surrounded by several neighbors, including Leo Minor, Cancer, Sextans, Hydra, Crater, Virgo, Coma Berenices, Lynx, and Ursa Major.

 

Asterism

Leo's famous asterism is The Sickle, which consists of a pattern of six stars that form the head of the celestial lion. To most observers, it appears like a backward question mark in the sky and is one of the easiest star patterns to recognize.

The Sickle consists of the following stars:

  • Regulus (Alpha Leonis) – The brightest star in Leo, marking the bottom of the sickle or question mark.
  • Eta Leonis – A variable blue-white double star.
  • Algieba (Gamma Leonis) – A golden-hue binary star system with two giant stars.
  • Adhafera (Zeta Leonis) – A yellow-white giant star.
  • Rasalas (Mu Leonis) – An orange giant star.
  • Epsilon Leonis – A bright yellow giant star.

Together, these six stars outline the curved shape of the lion's head. Use your imagination to outline the rest of the nearby stars to form Leo's body and tail. The star Denebola marks the tip of the lion's tail.

 

Prominent Stars

  • Regulus (Alpha Leonis) is Leo's brightest star, the "Heart of the Lion." It is a blue-white multiple-star system with an apparent magnitude of +1.40. It lies about 79 light-years away.
  • Denebola (Beta Leonis) marks the tip of Leo's tail and is a young white main-sequence star approximately 36 light-years from Earth. It is the second-brightest star in Leo and has an apparent magnitude of +2.14.
  • Algieba (Gamma Leonis) is a beautiful, golden-hue binary star system with two giant orange stars. To the naked eye, they appear as a single point of light. Their apparent magnitudes are +2.37 and +3.64.
  • Zosma (Delta Leonis) is a white main-sequence star, forming the top of the triangular pattern of Leo's rear end. It is 58.4 light-years from Earth and has an apparent magnitude of +2.56.
  • Chertan (Theta Leonis) is a white main-sequence star, marking part of the lion's hindquarters. It is approximately 165 light-years away, with an apparent magnitude of +3.32.
  • Adhafera (Zeta Leonis) is a yellow-white giant star in the lion's mane above Algieba in the Sickle. Its Arabic name, meaning "lock of hair," is fitting. It is 274 light-years from Earth and has an apparent magnitude of +3.33.
  • Rasalas (Mu Leonis) is an orange class giant at the top of the Sickle, which signifies Leo's head. It is located 133 light-years from Earth and shines at an apparent magnitude of +3.88.

 

Deep-Sky Objects

Leo boasts a spectacular collection of deep-sky wonders, particularly galaxies that captivate astronomers. Here are some of the most remarkable ones:

Leo Triplet (M66 Group): A trio of interacting spiral galaxies—Messier 65, Messier 66, and NGC 3628 (Hamburger Galaxy). M65 and M66 were discovered by Charles Messier in 1780, while NGC 3628 was discovered by William Herschel in 1784. They are located about 35 million light-years from Earth and are known for their gravitational interactions, distorting their shapes. These galaxies are relatively bright and can be observed with small and large telescopes under dark skies. M65 (magnitude +9.3), M66 (magnitude +8.9, and NGC 3628 (magnitude +9.5). All three galaxies can be seen in the same field of view in a Celestron 11" SCT or EdgeHD telescope with a 31mm Luminos eyepiece!

Messier 95 (NGC 3351) is a beautiful, barred spiral. It was discovered by Pierre Méchain in 1781 and cataloged by Charles Messier four days after its discovery. M95 is part of the M96 Group (Leo I Group), which includes Messier 96 and Messier 105. M95 is about 33 million light-years away from Earth and has an apparent magnitude of +9.72.

Messier 96 (NGC 3368) is a spiral galaxy that forms a pair with Messier 95. Both galaxies were discovered by Pierre Méchain in 1781 and later added to Charles Messier's famous catalog. M96 is a member of the same Leo I group of galaxies, including M95, M65, M66, M105, and more. M96 is 41 million light years away from Earth and is the brightest of this group, with an apparent magnitude of +9.2. SN 1998bu, a bright supernova, was observed in M96.

Messier 105 (NGC 3379) is an elliptical galaxy of the Leo I Group. It features a smooth structure similar to a fuzzy ball, unlike the spiral structures of other galaxies. Pierre Méchain discovered M105 in 1781, just a few days after finding M95 and M96. It is about 36.6 million light-years away with an apparent magnitude of +9.25, visible in small and medium telescopes. The Hubble Space Telescope revealed that M105 contains a supermassive black hole.

NGC 2903 is a striking barred spiral galaxy discovered by William Herschel in 1784—yet, surprisingly, it was never included in Charles Messier's famous catalog. This galaxy is well known for its starburst activity in its central region, where new stars form rapidly. NGC 2903 is about 30 million light-years from Earth and has an apparent magnitude of +8.9, making it visible in telescopes of all sizes. NGC 2903 is often considered one of the best galaxies to observe that isn't part of the Messier list.

NGC 3521, also known as the Bubble Galaxy, is a spiral galaxy with a flocculent structure, giving it a "fluffy" appearance rather than distinct, well-defined spiral arms. William Herschel discovered it in 1784, describing it as "very bright, much elongated, and much brighter in the middle." NGC 3521 is approximately 40 million light-years from Earth and has an apparent magnitude of +11.0. However, its surface brightness is around +13.2, making it challenging to see, even with a telescope. NGC 3521 has numerous patches of star-forming regions throughout its disk.

 

How to See the Leonids Meteor Shower

The Leonids are an average meteor shower, active between November 6 and November 30, 2025, and may produce up to 15 meteors per hour at its peak. What is unique about this meteor shower is its cyclonic peak, which occurs about every 33 years. During the cyclonic peak, thousands upon thousands of meteors can rain down. Its most famous outbursts were the "Great Meteor Storms" in 1833 and 1966. The last storm occurred in 2002, so we aren't due for another one this year. Because the Earth runs head-on into the Comet Tempel-Tuttle's debris field, Leonid meteors travel much faster than other storms (45 miles per second). The Leonids peak on the morning of November 18, 2025, and the waning crescent Moon will not interfere throughout most of the night, making conditions ideal for viewing the shower. Face towards the constellation Leo the Lion, the shower’s radiant point. But remember, Leonid meteors can appear anywhere in the sky.

 

Final Thoughts

As we gaze into the night sky, Leo is a timeless guide for astronomers and stargazers alike. With its rich mythology, unique star patterns, and many island galaxies, Leo is a centerpiece of springtime observations. Whether you're following the path of the celestial lion or uncovering the deep-sky treasures within, Leo invites us to explore the vastness of space and deepen our connection with the cosmos. Clear skies!