Asterism (astronomy) - Large Seasonal Asterisms

Large Seasonal Asterisms

Component stars of seasonal asterisms are bright and mark out simple geometric shapes.

• Spring. Spring is marked by the Diamond of Virgo consisting of Arcturus, Spica, Denebola, and Cor Caroli. An East-West line from Arcturus to Denebola forms an equilateral triangle with Cor Caroli to the North, and another with Spica to the South. The Arcturus, Denebola, Spica triangle is given the name Spring Triangle. Together these two triangles form the Diamond. Formally, the stars of the Diamond are located in the constellations Boötes, Virgo, Leo, and Canes Venatici.

• Summer. The Summer Triangle of Deneb, Altair, and Vega — α Cygni, α Aquilae, and α Lyrae — is easily recognized, as its three stars are all of the 1st magnitude. The stars of the Triangle are located in the band of the Milky Way which marks the galactic equator, and are in the direction of the galactic center.

• Autumn. The Great Square of Pegasus is the quadrilateral formed by the stars α Pegasi, β Pegasi, γ Pegasi, and α Andromedae, representing the body of the winged horse. It may be glimpsed in its entirety on autumn nights. The asterism was recognized as the constellation ASH.IKU "The Field" on the MUL.APIN cuneiform tablets from about 1100 to 700 BC.

• Winter. The winter midnight sky of the northern hemisphere is dominated by Orion, in the direction opposite the galactic center. Also, one-third of the 1st-magnitude stars visible in the sky (seven of twenty-one) are in the Winter Hexagon with Sirius, Procyon, Pollux, with 2nd-magnitude Castor - Capella, Aldebaran, and Rigel on the periphery, and Betelgeuse located off-center. Although somewhat flattened, and thus more elliptical than circular, the figure is so large that it cannot be taken in all at once, thus making the lack of true circularity less noticeable. (The projection in the chart exaggerates the stretching.) Some prefer to regard it as a Heavenly 'G'.