Capricornus is in the "water-oriented" part of the fall sky, along with Pisces, Aquarius, and Cetus. It can be seen in early autumn, reaching its highest point in September. It is usually not very plainly seen until mid autumn. It does not much resemble a goat, but has been described by some as an inverted hat or as a bikini bottom. In the Northern Hemisphere, it appears low along the southern horizon, but from the Southern Hemisphere, it is high in the northern sky in spring.
History and Mythology
Capricornus has a rich mythology. Some of the gods, including Pan, were feasting along the banks of the Nile. During their feast the monster Typhon came upon them. The other gods transformed themselves into animals to escape the monster. The god Pan, who was very excitable, jumped into the Nile to escape the giant Typhon. He didn't allow enough time to transform himself. While his head was still above water, it became the head of a goat. His lower half became the back part of a fish. Today's English word "panic" comes from the excitable Pan.
Another ancient legend claims that the constellation is the gate that men must pass through if they wish to travel to heaven. It is called the Gate of the gods.
Several thousand years ago, the Sun passed through Capricornus during the winter rainy season, so that to this day the constellation is associated with water. When Capricornus rose in the sky, the farmers knew it would soon rain.
The sea goat, which was a symbol of fertility, is associated with Roman mythology. The goat was named Amalthea, and this goat suckled Zeus when he was an infant. Some claimed that the Sun, which at this time was in Capricornus at midwinter, took nourishment from the goat before it would begin its climb back northward.
Notable Stars
The brightest stars of Capricorn are arranged in a large triangle, which is slightly bowed along the sides. Alpha Capricorni is a naked eye double star, with 4th-magnitude components separated by about 1/6th the width of the full Moon. It is also an "optical double" star, meaning that its components are physically unrelated; they are both yellow giants lying at distances of 109 and 690 light years. These components have the common names Algedi (or Geidi) Prima and Algedi (or Geidi) Secunda; Algedi derives from the Arabic word for "billy goat".
Another wide double star in this constellation is Beta Capricorni, known as Dabih, meaning "lucky star of the slaughterer" in Arabic, which refers to the ritual of sacrificing goats in ancient times. This double's components are a 3rd magnitude blue-white star and a 6th magnitude orange giant, some 330 light years away. They do actually appear to be related, although they take at least 700,000 years to orbit each other.
Gamma Capricorni, also called Nashira, is blue-white 4th-magnitude giant star 140 light years away. Its name comes from the Arabic phrase for "bearer of good news". Delta Capricorni is a white 3rd-magnitude star only 40 light years away. Its traditional name Deneb Algedi means "tail of the goat" in Arabic.
Clusters, Nebulae, and Galaxies
The globular cluster M 30 is the most prominent deep sky object in the constellation. It is a compact cluster easily seen in an 8-inch telescope.
NGC 6907 is a barred spiral galaxy located on the western edge of the triangle of Capricornus. It appears as a fuzzy, elongated patch in a 10-inch telescope.