Know your constellations: Sagittarius the Archer – also known as the Teapot

Know your constellations: Sagittarius the Archer – also known as the Teapot

Published by Nick Lomb on August 25, 2011 No Comments

Sagittarius

The stars of the constellation of Sagittarius the Archer. As indicated on the drawing, the constellation has an informal alternative name of the Teapot. The positions of the two best known nebulae in the constellation, Messier 8 and Messier 20, are also shown. Image and copyright Nick Lomb ©, all rights reserved with the drawing of the teapot from Microsoft clip art

In August/September the constellation of Sagittarius the Archer is almost overhead in the early evening as seen from Australia. It is one of the 13 constellations of the Zodiac, that is it is one of the 13 constellations in front of which the Sun moves during the year, and it is the constellation that follows Scorpius the Scorpion. It is normally drawn as a half–man half–horse creature, known as a centaur, with a bow and arrow in its hands. The lower two stars Rukbat and Arkab represent the creature’s left foreleg.

As usual with ancient constellations, a lot of imagination is neeeded to see this group of stars as a centaur. Instead, to modern eyes some of the brighter stars of the constellation clearly outline a teapot. The stars Kaus Media, Kaus Australis and Alnasi represent the spout, the stars Kaus Media, Kaus Borealis and the star to the right of Nunki represent the lid while Nunki, the star to its right, Ascella and the star to its left represent the handle. Once seen in this way the constellation becomes quite unmistakeable.

The brightest star of the constellation is Epsilon Sagittarii or Kaus Australis, meaning the Southern Bow. It is a hot white star that is 140 light years from us. Delta Sagittarii is known as Kaus Media, meaning the Middle of the Bow. This is an orange coloured star at a distance of 300 light years.

A few other stars of Sagittarius:

Gamma Sagittarii or Alnasi, meaning the point. It is an orange coloured star at a distance of 100 light years.
Zeta Sagittarii or Ascella, meaning the Armpit. It is a double star in which the components take 21 years to circle each other. The stars are 90 light years away.
Sigma Sagittarii or Nunki, meaning the Star of the Proclamation of the Sea. This wonderful name seems to refer to the fact that the following zodiac constellations, Capricornus, Aquarius and Pisces, are all associated with to water. It is a hot blue-white star that is 224 light years away.

The constellation contains a number of nebulae. One of these is the famous M8 or the Lagoon Nebula that is a huge cloud of gas and dust illuminated by a cluster of newly formed stars. Another famous object in Sagittarius is M20 or the Trifid Nebula that has three clearly visible dark lanes of dust in front of the bright part of the nebula.

Sagittarius is an excellent target through binoculars or through a small telescope. On a clear evening go outside and have a look!

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