Leo, the Lion, is one of the twelve constellations of the Zodiac. It is one of the few constellations that actually resembles the object or animal for which it is named. In Greek mythology, Leo was identified as the Nemean lion, which Hercules strangled as the first of his twelve labors. Leo is located between the constellations Cancer and Virgo, but can be found most easily by extending an imaginary line backward through the pointer stars of the Big Dipper’s bowl.
Leo is visible before midnight to northern-hemisphere sky observers from late autumn until the following July. This article will discuss some of the highlights of this constellation, including its brightest stars as well as deep-sky objects visible through a telescope.
It is easiest for amateur sky watchers to find Leo in relation to the Big Dipper. In the late fall and winter months, Leo is rising in the eastern sky to the right of the Dipper. During spring, Leo is overhead, and by early summer, Leo is setting in the west to the left of the Big Dipper.
Once you have located Leo, you will notice that its brightest stars form two distinct shapes: an isosceles triangle that marks the Lion’s hindquarters and a backward question mark, sometimes called the Sickle, which forms the Lion’s head. The bluish white star at the end of the Sickle is Regulus (alpha Leonis). The name Regulus means prince, and, centuries ago, astrologers designated it one of the four “royal stars,” along with Aldebaran, Antares and Fomalhaut.
At magnitude 1.36, Regulus is the brightest star in Leo and the twenty-first brightest star in the night sky. Regulus is located 77 light years from Earth, and, as a blue giant star, shines some 140 times brighter than the Sun. Located close to the ecliptic plane, Regulus is occasionally occulted by the full moon. In terms of apparent magnitude, the next brightest stars in Leo include Denebola (beta Leonis), which marks the Lion’s tail; Algieba (gamma Leonis), in the Lion’s mane; and Zosma (delta Leonis), located northeast of Denebola at the apex of the triangle.
Leo contains several deep-sky objects, including M65, M66, M95, M96 and M105. The “M” prefix was chosen in honor of Charles Messier, an 18th-century French astronomer, who compiled a list of star clusters, nebulae and galaxies that amateur astronomers often mistook for comets. All of the Messier objects in Leo are spiral galaxies, except for M105, which is an elliptical galaxy. None of these galaxies is visible to the naked eye, but at 9th and 10th magnitudes can be seen with a medium-size or large telescope.