Constellation of Capricornus

Abbreviation: Cap

Genitive: Capricorni

English: The Sea Goat

Size Ranking: 40th

Area: 414 square degrees.

Capricornus is the smallest in the Zodiac, and lies between Sagittarius and Aquarius, and originated among the Babylonian and Sumerian peoples of the Middle East. Amphibious creatures feature prominently in ancient legends, and the origin of Capricornus, being depicted as a goat with a fish’s tail, dates back to ancient Greek times. The constellation represented the goat headed god Pan who jumped into a river to escape the approach of the monster Typhon, turning his lower half into a fish. Before 130BC, the Sun lay in Capricornus when it reached its farthest point south of the equator each year; this point, known as the northern winter solstice, currently occurs in late December. The latitude on Earth at which the Sun was directly overhead at noon on that date, 23½°south, became known as the Tropic of Capricorn. Because of precession, the northern winter solstice  has moved into the neighbouring constellation Sagittarius, but the Tropic of Capricorn still retains its name.

To locate Capricornus, refer to the constellation of Sagittarius. Starting at εSgr, at the base of the Teapot’s spout, imagine a line running out through τSgr, the eastern point of the Teapot’s handle, to meet at αCap, such that the distance αCap to τSgr is 1.8 times the distance τSgr to εSgr.


Features of Interest:

αCap, named Algedi or Giedi, both from the Arabic meaning ‘the kid’, is a multiple star, consisting of an unrelated yellow supergiant, α², of magnitude 4.3 and a yellow giant, α¹, of magnitude 3.6, 690 and 109ly away respectively; separation 378”, PA 291°.

Each star is itself a double. α¹ has a wide companion, magnitude 9.2, separation 45”, PA 221°. α² has its own companion, magnitude 11.0, separation 6.6”, PA 172°. Telescopes of appropriate quality and power will reveal that the fainter companion of α² is composed of two 11th magnitude stars. αCapricorni is therefore a fascinating hybrid system.

βCap, named Dahib, from the Arabic meaning ‘the lucky stars of the slaughterer’, is a golden-yellow giant star of magnitude 3.1, 340ly distant.

γCap, named Nashira, is a white giant star, 139ly away and magnitude 3.7.

δCap, named Deneb Algedi, ‘the kid’s tail’, at magnitude 2.9, is the brightest star in the constellation. It is an eclipsing binary of the βLyrae type, varying by a miniscule 0.2 magnitude over 24.5hrs. It lies 39ly away.

πCap, 670ly away, is a blue-white star of magnitude 5.1 with a 8.3 magnitude companion, separation 3.2”, PA 148°.

M30 (NGC 7099), is a magnitude 7.5 globular cluster 30,00ly away; diameter 11’.



1. Redshift 2 – Maris Multimedia

2. The Guiness Book of Astronomy – Patrick Moore

3. Stars and Planets – Ian Ridpath and Wil Tirion

4. Sky Charts – Cartes du Ciel V 2.75.