A Guide to Asterisms - The Unofficial ConstellationsAsterisms are patterns of stars that are either part of a constellation or entirely separate. The most famous asterism is the Big Dipper.
Asterisms are patterns of stars (similar to constellations) that are either part of a constellation or entirely separate. They are as old as the constellations and as well known but are not recognised as official constellations. The most famous asterism is the plough or big dipper. This asterism consists of a group of stars that make up Ursa Major's constellation. Some asterisms span multiple constellations.
Like the constellations, asterisms date back to the dawn of humankind. The only difference between a constellation and an asterism is that a constellation is a name given to an officially recognised asterism. Eighty-eight constellations divide the entire sky, and all the others are asterisms.
Big Dipper AKA The Plough
The most famous of all asterisms is formed by the stars Dubhe (α UMa), Merak (β UMa), Phecda (γ UMa), Megrez (δ UMa), Alioth (ε UMa), Mizar (ζ UMa) and Alkaid (η Uma).
Diamond of Virgo
Spring is marked by the Diamond of Virgo consisting of Arcturus (α Bootis), Spica (α Virginis), Denebola (β Leo), and Cor Caroli (α Canum Venaticorum). An East-West line from Arcturus to Denebola forms an equilateral triangle with Cor Caroli to the North (Spring Triangle) and another with Spica to the South. Together, these two triangles form the Diamond. The Diamond is too large to be seen simultaneously as it spans both the north and south hemispheres.
Great Square of Pegasus Asterism
The Great Square of Pegasus is the quadrilateral that forms the body of the winged horse. It may be glimpsed in its entirety on autumn nights.
Heavenly G Asterism
Nine bright stars forming a G-shaped group. Seven of these stars are of 1st magnitude. Aldebaran (α Tau), Capella (α Aur), Castor (α Gem), Pollux (β Gem), Procyon (α CMi), Sirius (α CMa), Rigel (β Ori), Bellatrix (γ Ori) and Betelgeuse (α Ori)
Hydra Head
Built by Mautinah (δ Hya), Ashlesha (ε Hya), Hydrobius (ζ Hya), η Hya, ρ Hya and Minchir (σ Hya).
Keystone Asterism
The four central stars in Hercules, ε ζ η and Io
Lozenge
A small diamond formed from three stars, Eltanin (γ Dra), Grumium (ξ Dra), and Rastaban (β Dra), in the head of Draco and ι Herculis in the foot of Hercules.
Northern Cross
Northern Cross consists of part of the constellation Cygnus. The upright runs from Deneb (α Cyg) in the Swan's tail to Albireo (β Cyg) in the beak. The transverse runs from Gienah (ε Cyg) in one wing to δ Cyg in the other.
Orion's Belt
Another famous asterism, the Orion's Belt is formed by the stars Alnitak (ζ Ori), Alnilam (ε Ori) and Mintaka (δ Ori).
Orion's Scabbard
Orion's scabbard is actually the Nebulae M42 and M43, The Great Orion Nebula.
The Sickle
The sickle is formed by the stars making Leo's head, α Leo, η Leo, γ Leo, ζ Leo, mu Leo and ε Leo.
Summer Triangle
Triangle of Deneb (α Cygni), Altair (α Aquilae), and Vega (α Lyrae) is easily recognised 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.
Teapot
The bow and arrow of the Archer Sagittarius also make a well-formed Teapot. There is even a bit of nebulosity near the "spout" to serve as steam.
