Spring Triangle

A formation of three stars prominent in the skies of the northern hemisphere during the period from March to May each year. The Spring Triangle connects bright stars within the constellations of Boötes, Virgo and Leo, though different sources prefer to form the Spring Triangle from slightly different combinations of three stars.

The brightest member of the Spring Triangle is Arcturus in Boötes, which is indeed the brightest star in the entire northern sky. One leg of the triangle connects Arcturus southward to blue Spica in Virgo. The triangle's third corner lies westward of the other two, and is most commonly seen as reaching to Regulus, another bright blue star in Leo.

A triangle connecting Arcturus, Spica and Regulus is rather elongated in form, and some sources prefer to replace Regulus with Denebola, the star marking the tail of the Lion. Denebola is not quite so bright in the sky as Regulus, but the resulting triangle is much closer to having equal sides. Arcturus, Spica and Denebola together form the vertices of another, larger, formation known as the Great Diamond or Diamond of Virgo, which connects those three stars with Cor Caroli to the north. So, if Denebola is used as part of the Spring Triangle, then that triangle forms the southern half of the Great Diamond.

Regardless of the particular combination of stars used, the northern edge of the Spring Triangle (running between Arcturus and Leo) cuts through the southern parts of Coma Berenices, and so the many galaxies of the Virgo Cluster can be found within the Triangle's northern parts. If the star Regulus is used as the western angle, then the galaxies ranged through southern Leo are also incorporated within the northern edge of the triangle shape.