Celestial Wonders in Leo – NASA Science
Leo is an important sight for astronomers in April. Its famous sickle, punctuated by the bright star Regulus, catches the eyes of many beginning astronomers, inviting a deeper look at some of Leo’s celestial delights, including a large double star and a famous galactic trio.
Leo’s distinctive front sickle, or “inverted question mark,” is easy to spot as it climbs the southeastern skies after sunset. If you have trouble spotting the sickle, look for the brilliant Sirius and Procyon in Canis Major and Canis Minor. Complete a triangle by drawing two lines eastward, joining at the bright star Regulus, the “dot” in the inverted question mark. Behind them is a trio of bright stars forming an isosceles triangle, with the brightest star in this formation being named Denebola. The connection of these two motifs forms the constellation Leo the Lion, with the forward-facing sickle being the lion’s head and mane, and the rear triangle its hindquarters. Can you see this powerful feline? It might help to imagine Leo sitting proudly and looking straight ahead, like a celestial sphinx. To help you find these items, you can use online tools like Stellarium Web.
If you peer deeper into Leo with a small telescope or binoculars, you will discover a remarkable double star! Look in Leo’s Sickle for its second brightest star, Algieba, also called Gamma Leonis. This star splits into two bright yellow stars, even at low magnification. You can achieve this “separation” with binoculars, but it is more obvious with a telescope. Compare the color and intensity of these two stars: do you notice any differences? There are other multiple star systems in Leo; spend a few minutes scanning with your instrument of choice and see what you discover.
One of the most famous sights in Leo is the “Lion Triplet”: three galaxies that appear close to each other. They are in fact gravitationally linked to each other, approximately 30 million light years away! You’ll need a telescope to spot them, and use an eyepiece with a wide field of view to see all three galaxies at once! Look under the star Chertan to find galaxies M65, M66 and NGC 3628 – the Hamburger galaxy. Compare and contrast the appearance of each galaxy: even though they are all spiral galaxies, each is tilted at different angles from our perspective! Do they all look like spiral galaxies to you?
April is Citizen Science Month, and you can participate in fun Lions-related activities! If you like
By comparing the Triplets, the Galaxy Zoo project could use your eyes to help classify different galaxies from sky survey data! Observing Leo itself can even help measure light pollution: the Globe at Night project uses Leo as a target constellation for observations of sky quality from the Northern Hemisphere. Find and participate in many other NASA community science programs on NASA Citizen Science. Good observation!
Originally published by Dave Prosper: April 2021
Last updated by Kat Troche: April 2026
