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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, 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 a name given to an officially recognised asterism. There are 88 constellations that divide the entire sky all the others are asterisms.

Big Dipper Asterism

Big Dipper, Plough Constellation

Big Dipper, Plough Constellation

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

Great Square of Pegasus

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 Asterism

The four central stars in Hercules, ε ζ η and Io

Lozenge Asterism

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

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

Orion Low in the Horizon

Orion Low in the Horizon

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

Orion's Scabbard

Orion's scabbard is actually the Nebulae M42 and M43, The Great Orion Nebula.

The Sickle

The Sickle

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

Summer Triangle

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 Asterism

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.

One thought on “A Guide to Asterisms – The Unofficial Constellations
  • 15th December 2009 at 12:00 am

    Thanks for the wonderful information. Someone asked what an Asterism is, and I had no idea. I googled it and your site popped up. I saved it to my favourites -so much to learn. I didn't realize.
    Thanks again,
    Linda

    Reply

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