Asterism astronomy: Encyclopedia II - Asterism astronomy - Other examples

Asterism astronomy - Other examples

Undoubtedly, the best-known asterism is the Big Dipper. Composed of the seven brightest stars in Ursa Major where they delineate the Bear's hindquarters and exaggerated tail, the Dipper is often the first grouping of stars shown to beginners in the Northern Hemisphere.

With its even more ridiculously lengthened tail, Ursa Minor hardly appears bearlike at all. It does much better under its pseudonym of the Little Dipper.

Ursa Minor is not the only constellation that does not look very much like what it represents. Very few do. This has led to nicknames for some of the constellations. These nicknames are another variety of asterism. A glance at the stick-figures shown in the charts under the constellation names will easily explain the origin of these asterisms.

• The best-known of this type is the Northern Cross in Cygnus. The upright runs from Deneb (α Cyg / Alpha Cygni) in the Swan's tail to Albireo (β Cyg / Beta Cygni) in the beak. The transverse runs from Gienah (ε Cyg / Epsilon Cygni) in one wing to Delta Cygni (δ Cyg) in the other.
• The Great Hook is the traditional Polynesian name for Scorpius. The image will be even more obvious if the chart's lines from Antares (α Sco / Alpha Scorpii) to Graffias (β Sco / Beta Scorpii) and Pi Scorpii (π Sco) are replaced with a line from Graffias through Dschubba (δ Sco / Delta Scorpii) to Pi.
• Adding vertical lines to connect the limbs at the left and right in the main diagram of Hercules will complete the figure of the Butterfly.
• Although hardly an ancient notion, it is easy to see why the Ice Cream Cone is sometimes applied to Boötes. It is even better-known as the Kite.

An asterism may also be a section of a constellation that refers to the figuring of the whole. Thus, for example, there are:

• Orion's Belt;
• The Urn in Aquarius;
• Hercules' Club.

There are many others.

There is another asterism which, like the Diamond of Virgo, is composed of a pair of equilateral triangles. Sirius (α CMa / Alpha Canis Majoris), Procyon (α CMi / Alpha Canis Minoris), and Betelgeuse (α Ori / Alpha Orionis) form one triangle while Sirius, Phaet (ζ Pup / Zeta Puppis), and Naos (α Col / Alpha Columbae) form another. Unlike the Diamond, however, these triangles meet, not base-to-base, but vertex-to-vertex, forming the Egyptian X. The name derives from both the shape and, because the stars straddle the Celestial Equator, it is more easily seen from south of the Mediterranean than in Europe.

The Lozenge is a small diamond formed from three stars - Eltanin ( γ Dra / Gamma Draconis), Grumium (ξ Dra / Xi Draconis), and Rastaban (β Dra / Beta Draconis) - in the head of Draco and one - Iota Herculis (ι Her) - in the foot of Hercules.

The False Cross is composed of the four stars Delta and Kappa Velorum (δ and κ Vel) and Epsilon and Iota Carinae (ε and ι Car). Although its component stars are not quite as bright as those of the Southern Cross, it is actually somewhat larger and better shaped than the official constellation.

The four central stars in Hercules, ε (Epsilon), ζ (Zeta), η (Eta), and π (Pi), form the well-known Keystone.

The curve of stars at the front end of the Lion from Al Ashfar (ε Leo / Epsilon Leonis) to Regulus (α Leo / Alpha Leonis), looking much like a mirror-image question mark, have long been known as the Sickle.

The bow and arrow of the Archer also make a well-formed Teapot. (There is even a bit of nebulosity near the "spout" to serve as steam.)

There are two pairs of stars known as The Pointers:

• One pair consists of Dubhe and Merak (Alpha and Beta Ursae Majoris), the two stars at the end of the bowl of the Big Dipper. A line from β to α and continued for a bit over five times the distance between them, arrives at the North Celestial Pole and the star Polaris (α UMi / Alpha Ursa Minoris), the North Star.
• Less useful are Alpha and Beta Centauri which point to Crux which is easily spotted on its own. However, the stars marking the upright of the Southern Cross itself can, themselves, be used to locate the South Celestial Pole. Extending a line from Gacrux (γ Cru / Gamma Crucis) to Acrux (α Cru / Alpha Crucis) and continuing it for a bit under five times the distance between them does the trick although there is no bright star to mark the spot.

Asterisms range from the large and obvious to the small, and even telescopic. Examples of the latter include:

• The Coathanger
• Kemble's Cascade.

Adapted from the Wikipedia article "Other examples", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki