Capricornus Constellation


Capricornus constellation is located in the southern sky.

Its name means “the goat” in Latin.

Capricornus is one of the 12 zodiac constellations and it is represented by the symbol ♑.

It was one of the constellations originally catalogued by the Greek astronomer Ptolemy in the 2nd century.

Capricornus is home to several notable stars as well as to the famous globular cluster Messier 30.

FACTS, LOCATION & MAP

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Capricornus Constellation Map, by IAU and Sky&Telescope magazine

Capricornus is the 40th biggest constellation in the sky, occupying an area of 414 square degrees.

It lies in the fourth quadrant of the southern hemisphere (SQ4) and can be seen at latitudes between +60° and -90°.

The neighboring constellations are Aquarius, Aquila, Microscopium, Piscis Austrinus, and Sagittarius.

Capricornus has three stars with known planets and also contains a Messier object, M30 (NGC 7099).

The brightest star in the constellation is Deneb Algedi, Delta Capricorni.

There are five meteor showers associated with Capricornus: the Alpha Capricornids, the Chi Capricornids, the Sigma Capricornids, the Tau Capricornids, and the Capricorniden-Sagittarids.

Capricornus belongs to the Zodiac family of constellations, along with Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Aquarius, and Pisces.


MYTH

Even though Capricornus is the second faintest constellation in the sky, after Cancer, it is associated with myths and images that go way back to the 21st century BC.

The story of Capricornus originated with the Babyonians and Sumerians. The Sumerians knew it as the goat-fish, or SUHUR-MASH-HA, while the Babylonian star catalogues dating back to 1000 BC mention the constellation as MUL.SUHUR.MAŠ, also meaning “goat fish.” In the early Bronze Age, Capricornus marked the winter solstice and, in modern astrology, Capricorn’s rule still begins on the first day of winter.

The Greeks associated the constellation with the forest deity Pan, who had the legs and horns of a goat. Crotus, his son, is usually identified with another amphibious creature, represented by the neighboring constellation Sagittarius.

Pan was placed in the sky by Zeus in gratitude for his coming to the other gods’ rescue on several occasions. During the gods’ war with the Titans, Pan helped scare the Titans away by blowing his conch shell and, later, he warned the gods that Typhon, a monster sent by Gaia to fight the gods, was approaching. He also suggested that the gods disguise themselves as animals until the danger passed.

In the myth, Pan eluded the monster himself by jumping into the river Nile and turning the lower part of his body into that of a fish. Zeus eventually killed Typhon with his thunderbolts and, in reference to the myth, Capricornus is still often depicted as a goat with the tail of a fish.

In another story, Capricornus is identified as Amalthea, the goat that suckled Zeus when he was an infant, hiding from his father Cronos. Cronos had devoured his other children, all future gods and goddesses, because of a prophecy that he would be overthrown by one of them.

MAJOR STARS IN CAPRICORNUS

Deneb Algedi – δ Capricorni (Delta Capricorni)

Delta Capricorni is the brightest star in the constellation, with an apparent visual magnitude of 2.85. The star is known by its traditional names Deneb Algedi and Sheddi. Deneb Algedi comes from the Arabic ðanab al-jady, which means “the tail of the goat.” The star is located near the ecliptic and can be occulted by the Moon and, very rarely, by planets.

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Conjunction of Mercury and Venus, with Gamma and Delta Capricorni to the right; photo: Y. Beletsky, ESO, March 2008

Deneb Algedi is a four-star system 39 light years from Earth. The brightest star, Delta Capricorni A, is a white giant that belongs to the spectral class A. It has the luminosity 8.5 times that of the Sun.

It is a spectroscopic eclipsing binary star. The unresolved companion star orbits with the giant around a common centre of mass every 1.023 days, resulting in the star’s luminosity dropping 0.2 magnitudes during the eclipses. Deneb Algedi is a Delta Scuti type variable, a star that varies in brightness due to both radial and non-radial pulsations of its surface.

Two other stars are believed to be orbiting in the system. Delta Capricorni C is a sixteenth magnitude star one arcminute away, while Delta Capricorni D, a thirteenth magnitude star, is two arcminutes away from the primary star.

Dabih – β Capricorni (Beta Capricorni)

Beta Capricorni is the second brightest star in Capricornus. Its traditional name, Dabih, comes from the Arabic al-dhābiḥ, which means “the butcher.”

Dabih is not a single star, but a star system, 328 light years distant, located near the ecliptic. It consists of Dabih Major (Beta-1 Capricorni), the brighter component, with an apparent magnitude of 3.05, and Dabih Minor (Beta-2 Capricorni), which has an apparent magnitude of 6.09. The two are separated by 3.5 arcminutes, or 0.34 light years, and complete one orbit every 700,000 years or so.

Both Dabih Major (Beta-1) and Dabih Minor (Beta-2) are composed of multiple stars. Beta-1 has at least three components. The brightest one is an orange K-type bright giant with an apparent magnitude of 3.08. The second brighest component is a blue-white B-type main sequence dwarf, which has a magnitude of 7.20. The two are separated by 0.05 arcsconds and have an orbital period of 3.77 years. The second component has an unseen companion that orbits it every 8.7 days.

Beta-2 Capricorni is a double star composed of an A0-class giant with a magnitude of 6.1, 40 times more luminous than the Sun, and a mercury-manganese star located about 3 arcseconds away.

Algiedi – α Capricorni (Alpha Capricorni)

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Algiedi (Alpha Capricorni), image Wikisky

Algiedi (or Algedi) is an optical binary star. Its name comes from the Arabic al-jady, which means “the billy goat.” It is composed of two star systems, Prima Giedi (Alpha-2 Capricorni) and Secunda Giedi (Alpha-2 Capricorni), which are separated by 0.11 degrees in the sky.

Alpha-1 Capricorni is a double star approximately 690 light years distant. It consists of a yellow G-type supergiant with a magnitude of 4.30, and an eight magnitude companion 0.65 arcseconds away.

Alpha-2 Capricorni is a yellow G-type giant, about 109 light years distant. It has a magnitude of 3.58 and is the brighter of the two components.

Nashira – γ Capricorni (Gamma Capricorni)

Nashira is a blue-white A-type giant, approximately 139 light years distant. Its name is derived from the Arabic phrase for “bearer of good news.” It has an apparent magnitude of 3.69 and lies close to the ecliptic. The star’s brightness varies by 0.03 magnitudes. It is classified as an Alpha-2 Canum Venaticorum type variable, a chemically peculiar star with strong magnetic fields.

Yen – ζ Capricorni (Zeta Capricorni)

Zeta Capricorni is a double star composed of a yellow G-type supergiant and a white dwarf. The system has an apparent magnitude of 3.77 and is approximately 398 light years distant. The brighter component is a Barium star that is particularly notable for having an overabundance of praseodymium.

Dorsum – θ Capricorni (Theta Capricorni)

Dorsum is a white A-type main sequence dwarf, about 158 light years distant. It has an apparent visual magnitude of 4.08. The star’s traditional name comes from the Latin word for “the back (of the goat).”

Baten Algiedi – ω Capricorni (Omega Capricorni)

Omega Capricorni is an M-type red giant star, approximately 630 light years from Earth. Its traditional name, Baten Algiedi (or Algedi), means “the belly of the goat” in Arabic. The star has an apparent magnitude of 4.12. It is a variable star, exhibiting regular variations in brightness and absolute magnitude.

ψ Capricorni (Psi Capricorni)

Psi Capricorni is a yellow-white giant belonging to the spectral class F5 V. It is 47.9 light years distant and has an apparent magnitude of 4.15.

DEEP SKY OBJECTS IN CAPRICORNUS

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Messier 30 (NGC 7099) in Capricornus, photo: Hubble Space Telescope (NASA, ESA)

Messier 30 (NGC 7099)

Messier 30 is a globular cluster approximately 28,000 light years distant and about 90 light years across in size.

The cluster is approaching us at the speed of 181.9 km/s. It was one of the first deep sky objects discovered by Charles Messier in 1764. The cluster has an overall spectral type F3.

M30 is relatively dense and belongs to the concentration class V. The brightest stars in the cluster are magnitude 12 red giants.

Like Messier 15, Messier 70, and many other globular clusters in the Milky Way Galaxy, M30 has undergone a core collapse. Its core is now only 0.12 arc minutes in size, and half of the cluster’s mass is contained in a spherical radius that is 17.4 light years across.

Messier 30 is easy to observe even in small telescopes.