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A Guide to Asterisms

What are asterisms and what are some interesting examples?

Written By on in Astronomy

548 words, estimated reading time 3 minutes.

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

The Big Dipper Asterism
The Big Dipper Asterism

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
The 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 π

 

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

The Northern Cross
The 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

The Belt of Orion
The Belt of Orion

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

The Summer Triangle
The 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.

Last updated on: Wednesday 24th January 2018

 

Comments
Linda

Linda

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 to Linda

 

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