Constellations of the Month: September – Capricornus:
We continue September with the next constellation of the month, Capricornus, “The Goat.”

Capricornus constellation map courtesy of Openverse

Capricornus, The “Goat” – The Capricornus constellation is a constellation located in the southern hemisphere, symbolizing the “goat.”  Its name translates to “the goat” in Latin. This constellation depicts a sea goat, a mythical being linked to the deity Enki in Babylonian lore and subsequently to the Greek god Pan. The symbol representing this constellation is ♑. Similar to other zodiac constellations, Capricornus was initially catalogued by the Greek astronomer Claudius Ptolemy in his work Almagest during the 2nd century CE. In Greek mythology, this constellation is connected to Pan, the god of nature, as well as to the goat Amalthea, who nourished Zeus in his infancy. The Capricornus constellation contains the eclipsing binary system Delta Capricorni (Deneb Algedi), the multiple star systems Beta Capricorni (Dabih) and Alpha Capricorni (Algedi), along with the white giant star Nashira (Gamma Capricorni). Among the notable deep sky objects found within this constellation are the globular clusters Messier 30 and Palomar 12, as well as the compact galaxy group HCG 87. Capricornus is a faint constellation located near the bright stars of Pegasus, Aquila, Sagittarius, and Piscis Austrinus. It is positioned between Enif, Altair, Ascella, and Fomalhaut.

Hickson Compact Group 87 courtesy of Openverse

Key points regarding Capricornus:

• Meaning: The term “Capricornus” translates to “The Goat” in Latin. Capricornus features five stars that have known planets and includes one Messier object, the globular cluster M30 (NGC 7099). The constellation houses three stars situated within 10 parsecs (32.62 light years) from the Sun. Deneb Algedi, also known as Delta Capricorni, is the brightest star in Capricornus, boasting an apparent magnitude of 2.81. It is the sole star in the constellation that exceeds a magnitude of 3.00. The constellation comprises five named stars. The names of these stars, as recognized by the International Astronomical Union (IAU), are Algedi, Alshat, Dabih, Deneb Algedi, and Nashira. Capricornus is associated with five meteor showers: the Alpha Capricornids, the Chi Capricornids, the Sigma Capricornids, the Tau Capricornids, and the Capricorniden-Sagittarids.
• Notable stars: Delta Capricorni, the brightest star in Capricornus, is a multiple star system located 38.70 light years from Earth, with an apparent magnitude of 2.81. Its main star, Deneb Algedi, is a giant star in an eclipsing binary that has two components orbiting every 1.022768 days. The brightness drops by 0.24 magnitudes when the fainter star eclipses the giant. Deneb Algedi is twice the mass of the Sun, with a surface temperature of 7,301 K and a luminosity 8.5 times that of the Sun. Beta Capricorni is 328 light years away and has an apparent magnitude of 3.05. It is a multiple star system with five stars, the main one being Dabih, an orange giant 600 times more luminous than the Sun. Alpha Capricorni has two star systems: Alpha1 and Alpha2. Alpha2 includes Algedi, a yellow giant, while Alpha1, Prima Giedi, is a yellow supergiant. Alshat is a double star near Alpha Capricorni, classified as a hot blue star. Nashira is a chemically peculiar Am star, and Zeta Capricorni is a binary system with a yellow giant and a white dwarf. Theta Capricorni and Omega Capricorni are additional stars in Capricornus with distinct characteristics.
• Other features: Messier 30 is a globular cluster approximately 27,140 light years away and 93 light years wide. It is moving toward us at 181.9 km/s and was discovered by Charles Messier in 1764. Its age is estimated at 12.93 billion years, and it has a concentration class V, with its brightest stars being magnitude 12 red giants. Messier 30 has experienced a core collapse, with a core size of 0.12 arc minutes. Hickson Compact Group 87 consists of galaxies 400 million light years away. The biggest, HCG 87a, is a spiral galaxy, while the others feature active galactic nuclei. IC 1337 is an intermediate spiral galaxy about 420 million light years away, discovered in 1892. Palomar 12 is a globular cluster located 63,600 light years away, with an age of 6.5 billion years and was once thought to be captured from a neighboring galaxy.
• Mythology: Capricornus is one of the dimmer constellations, with roots in myths from the 21^st century BCE. The Sumerians named it the goat-fish, known as SUHUR-MASH-HA, while the Babylonians called it MUL. SUHUR. MAŠ. In the early Bronze Age, it marked the winter solstice, and in modern astrology, Capricorn begins on the first day of astronomical winter. The Greeks linked Capricornus to Pan, a forest deity with goat legs and horns. He helped the gods during battles, warning them of dangers and advising them to disguise themselves. In the myth, Pan escaped a monster by turning his lower body into a fish. Capricornus is also related to Amalthea, the goat that nursed Zeus while he was hidden from Cronos, who had eaten his other children.
• Visibility: Capricornus is the 40^th largest constellation in the sky. It covers an area of 414 square degrees. It is situated in the fourth quadrant of the southern hemisphere (SQ4) and is visible at latitudes ranging from +60° to -90°. The constellations that border it include Aquarius, Aquila, Microscopium, Piscis Austrinus, and Sagittarius. The optimal time to observe Capricornus is in the month of September. The name Capricornus is pronounced /ˌkæprɪˈkɔːrnəs/. In English, it is referred to as the Sea Goat. The genitive form of Capricornus, which is utilized in the naming of stars, is Capricorni (pronunciation: /ˌkæprɪˈkɔːrnaɪ/). The three-letter abbreviation, which was established by the International Astronomical Union (IAU) in 1922, is Cap. Capricornus is part of the zodiac family of constellations, which also includes Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Aquarius, and Pisces. The constellation’s stars form a shape resembling two horns, marked by Deneb Algedi and Nashira at one end, and Algedi and Dabih at the other. The dim star Omega Capricorni is at the triangle’s base. Deneb Algedi is the only star in Capricornus brighter than magnitude 3.00, making the constellation hard to see in light-polluted areas.

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Constellations:

Sidney Hall’s (1831) astronomical chart illustration of the zodiac Capricornus. Original from Library of Congress. Digitally enhanced by rawpixel. courtesy of Openverse

Constellations of the Month:
September – Capricornus

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