Capricornus Constellation Facts, History & Stars

Capricornus is a southern sky constellation best recognized as being part of the zodiac. Contrary to popular belief, Capricornus is not represented by a goat, but rather a sea-goat: a half goat, half fish creature of Greek mythology.

It’s one of the 88 modern constellations and also featured in Ptolemy’s 48 listed constellations.

This constellation’s name is Latin for “horned goat”, but could also be interpreted as “goat horn” or even “having horns like a goat’s”. Capricornus is the smallest formation in the zodiac, though it does make the top 40 biggest constellations overall in the sky.

How to Locate Capricornus

Capricornus is bordered by a few prominent constellations including Aquila, Aquarius, Piscis Austrinus, Microscopium, and Sagittarius. Eridanus and Pisces are nearby too, and so this area of the sky has been donned the Sea because of its collection of water-related constellations.

Capricornus can be a bit difficult to spot if you don’t know what to look for. It’s one of the fainter constellations in the zodiac and does not look anything like a sea-goat. In fact, it’s usually described as a lopsided triangle.

The best way to spot it is to locate Sagittarius, which is far more obvious, first. Then follow the ecliptic to find Capricornus wedged between Sagittarius and Aquarius.

Another way to find this constellation from the northern hemisphere is to look for the Summer Triangle asterism. If you follow a line between Vega and Altair, Capricornus’s triangle lies just a little further along this trail.

For northern observers, Capricornus will hang low in the south of the sky. For those in the southern hemisphere, you’ll have to search higher in the northern region of the sky to view it. Regardless of your location, the best time to see Capricornus is early to mid-September, at around 10 pm.

Capricornus Mythology and History

Some of Capricornus’s myth has been lost in time, and historians are uncertain of its exact origins. The most accepted theory is that this myth can be traced quite far back in Greek mythology. Capricornus is associated with both Pan and Amalthea, though the stories regarding them vary significantly.

Where Pan is concerned, the tale goes that he warned the other gods of the arrival of Typhon; a water monster sent to destroy them. In an effort to trick Typhon he suggested that all the gods hide their appearances by taking on the form of animals. Pan, who had the legs and horns of a goat, hid away in the Nile. He also changed the lower half of his body to resemble a fish, giving rise to the myth of the sea-goat.  The gods evaded Typhon, who Zeus ultimately killed, and so Pan was placed in the sky as Capricornus as a reward for protecting them.

There isn’t as much evidence to suggest that Capricornus and Amalthea were the same character, but some stories imply that they were. In these renditions, Amalthea is the goat which suckles Zeus as an infant, while hiding away from Cronos, his father. Cronos had an intense fear due that one of his children would rise to defeat him – since this was prophesized – and so he would devour all his offspring in an effort to stop this from coming true.

Still, other sources state that Capricornus can be traced back as far as 1,000 BC, as part of Sumerian and Babylonian catalogs. We also know that back in the Bronze Age, Capricornus was the signifier of the winter solstice.

Stars in the Constellation Capricornus

Capricornus may be one of the faintest constellations to the naked eye, but there are still some fascinating points to look out for when you stargaze. It contains a collection of stars that are worth observing, three of which have known planets.

  • Delta Capricorni/ Deneb Algedi: With an apparent magnitude of 2.85, Delta Capricorni is the brightest binary star system in Capricornus. The star has a luminosity almost 9 times that of our Sun and is a white giant. There is an unresolved companion star orbiting Delta Capricorni, which drops the star’s luminosity by 0.2 magnitudes for the duration of these eclipses. It is a spectroscopic eclipsing binary star due to this and several other factors.

An additional two stars are also thought to orbit Delta Capricorni. They are Delta Capricorni C and Delta Capricorni D. The star system is close to the ecliptic and so can be occulted by the moon and to a less frequent degree, the planets too. It’s situated 39 light-years away from Earth. Its traditional name is derived from Arabic, and means “the tail of the goat”.

  • Beta Capricorni/ Dabih: This is the second brightest star in the constellation Capricornus. It is a star system comprised of Dabih Major and Dabih Minor. Dabih Major or Beta-1 Capricorni is the brighter of the system and has a visual magnitude of 3. Dabih Minor or Beta-2 Capricorni is magnitude 6. It takes several hundred thousand years to complete an orbit around each other.

Dabih Major has at least three stars in its system, the brightest of which is a giant star just under magnitude 4.0. Dabih Minor is a double star also containing a giant star. Beta Capricorni is 328 light-years away from us, and its traditional name, Dabih, stems from the Arabic for “the butcher”.

  • Alpha Capricorni/ Algiedi: Alpha Capricorni is an optical binary comprised of two systems. Alpha-1 Capricorni contains a yellow supergiant with a visual magnitude of 4.27, as well as an eight magnitude star. Alpha-2 Capricorni is a yellow giant star with a magnitude of 4.0. The traditional name, Algiedi, is a derivative of the Arabic for “billy goat”.
  • Gamma Capricorni/ Nashira: This is a giant blue/white star lying close to the ecliptic. It shines at magnitude 3.67 and is a variable star; its brightness typically varying by 0.03. Gamma Capricorni has strong magnetic field. Nashira comes from the Arabic phrase for “bearer of good news”. This star is approximately 139 light-years away from us.
  • Zeta Capricorni/ Yen: Zeta Capricorni is another double star, containing a yellow supergiant star and a white dwarf. Together, the stars shine 3.74. The brighter of the two is a Barium type star that stands out for its excess of the element praseodymium. Zeta Capricorni is almost 400 light-years away from us.
  • Omega Capricorni/ Baten Algiedi: Omega Capricorni is a red giant variable star with a visual magnitude of 4.11. The traditional name. The traditional Arabic name loosely means “the goat’s belly”. Omega Capricornus is approximately 630 light-years away from Earth.
  • Psi Capricorni: Psi Capricorni is a giant magnitude 4.15 star found nearly 50 light-years away from Earth.

Deep Sky Objects in Capricornus

Though Capricornus is a fairly large constellation, there is only one notable deep sky object within it: the famous Messier Object M30, a globular cluster.

  • M30/ NGC 7099: This globular cluster was one of the first of Charles Messier’s deep-sky finds, back in 1764. It is a popular target among amateur astronomers because it is easily viewed through binoculars, and viewing it through small telescopes is just as magnificent. The best time to view this cluster is August.

M30 is 28,000 light-years away from us and approaches us at a speed of 181.9 km/s. It spans roughly 90 light-years and is estimated to be almost 12.94 billion years old. Its combined mass is 160,000 times that of our Sun.

The exact way in which globular clusters are formed is not well-established yet, but some models suggest M30 is the result of a satellite dwarf galaxy, rather than a cluster which formed in the Milky Way. This is because it follows a retrograde orbit through the inner galactic halo.

Capricornus Meteor Showers

There are five meteor showers that originate in Capricornus; Alpha Capricornids, Chi Capricornids Sigma Capricornids, Tau Capricornids, and Capricornids-Sagittariids.

Of these Alpha Capricornids is the best for viewing and occurs between July 15th and August 10th. This meteor shower has relatively bright meteors for you to spot, but keep in mind that they are infrequent.