A Guide to Asterisms
A sub set of a constellation, asterisms consist of a group of stars that are either part of the main constellation or separate.
The most famous asterism is the plough or big dipper. This asterism consists of a group of stars, which make up the constellation of Ursa Major. Some asterisms span multiple constellations.
Like the constellations, asterisms date back to the dawn of mankind. The only difference between a constellation and an asterism is that a constellation is the name given to an officially recognised asterism. There are 88 constellations that divide the entire sky all the others are asterisms.
Big Dipper
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 all at once as it spans both north and south hemisphere.
Great Square of Pegasus
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
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
The four central stars in Hercules, ε ζ η and π
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.
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 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.
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.
