Equuleus constellation lies in the northern sky. Its name means “little horse” or “foal” in Latin.
The constellation is associated with several Greek myths, most notably the one about Hippe, the daughter of the centaur Chiron and the nymph Chariclo. The creator of the constellation is unknown, but Equuleus was introduced by the Greek astronomer Ptolemy in the 2nd century.
Equuleus is a small, faint constellation with few notable deep sky objects and no stars brighter than fourth magnitude. It is sometimes also known as Equus Primus, or the First Horse, because it rises just before the constellation Pegasus.
FACTS, LOCATION & MAP
Equuleus is the second smallest constellation in the night sky, after Crux (the Southern Cross). It occupies only 72 square degrees.
The constellation is located in the fourth quadrant of the northern hemisphere (NQ4) and can be seen at latitudes between +90° and -80°. The neighboring constellations are Aquarius, Delphinus and Pegasus.
Equuleus does not have any stars brighter than magnitude 3.00 or located within 10 parsecs (32.6 light years) of Earth. The brightest star in the constellation is Kitalpha, Alpha Equulei. The nearest star, HD 200779, is 48.41 light years distant from Earth. Equuleus contains three stars with known exoplanets. HD 200964 (spectral class K0IV) has two planets, while WASP-90 (F6) and HAT-P-65 (G2) have one transiting planet each.
Equuleus does not contain any Messier objects. There are no meteor showers associated with the constellation. Equuleus belongs to the Heavenly Waters family, along with Carina, Columba, Delphinus, Eridanus, Piscis Austrinus, Puppis, Pyxis, and Vela.
Equuleus, the foal, is usually associated with Hippe, the daughter of the centaur Chiron in Greek mythology. Hippe was seduced by Aeolus and became pregnant with his child. Too ashamed to tell her father, she hid the pregnancy from Chiron. She escaped to the mountains and stayed there until she gave birth to the child, named Melanippe.
When Chiron came looking for Hippe, she prayed to the gods that he doesn’t find her and they turned her into a mare. It was the goddess Artemis who placed Hippe among the constellations. She still appears to be hiding from Chiron, with only her head showing behind Pegasus. (Chiron is represented by the constellation Centaurus.)
Equuleus constellation is also sometimes associated with Celeris, a foal given as a present to Castor by Mercury. The name Celeris means “speed” or “swiftness.” The foal was either the brother or offspring of Pegasus, the famous winged horse, represented by the neighboring constellation.
MAJOR STARS IN EQUULEUS
Kitalpha – α Equulei (Alpha Equulei)
Alpha Equulei is a spectroscopic binary star of the spectral type G0III. It has a visual magnitude of 3.92 and is approximately 186 light years distant. It is the brightest star in Equuleus.
The star’s name, Kitalpha, is derived from the Arabic phrase qiṭ‘a(t) al-faras which means “a piece (or section) of the horse.”
Kitalpha is about 75 times more luminous than the Sun and has 2.72 times the mass.
δ Equulei (Delta Equulei)
Delta Equulei is another binary star in Equuleus. The components in the system belong to the spectral classes G0 and F5 and have visual magnitudes of 4.49 and 5.4. The system is approximately 60.3 light years distant from the Sun and has a combined apparent magitude of 4.47.
γ Equulei (Gamma Equulei)
Gamma Equulei, or 5 Equulei, is also a double star. It belongs to the spectral class A9 Sr Eu. It has a visual magnitude of 4.7 and is 118 light years distant.
Gamma Equulei is a chemically peculiar star that undergoes occasional variations in brightness and is also classified as a roAp star, or a rapidly oscillationg Ap star. (An Ap star is a peculiar star of the type A that shows an overabundance of certain metals and usually rotates much slower than regular A type stars.)
The companion star has an apparent magnitude of 9.05 and is located 1.26 arc seconds away from the main component.
β Equulei (Beta Equulei)
Beta Equulei is a main sequence star belonging to the spectral class A3V. It has four visual companions that are not physically related to the main star. The system has a combined apparent magnitude of 5.159 and is about 360 light years distant from Earth.
λ Equulei (Lambda Equulei)
Lambda Equulei is another binary star in the constellation. The primary component in the system is a main sequence star belonging to the spectral class F6V. The system has an apparent magnitude of 6.72 and is approximately 332 light years distant from the solar system.
ε Equulei (Epsilon Equulei)
Epsilon Equulei is another multiple star in Equuleus. It consists of four components. It has a visual magnitude of 5.3 and is 196.4 light years distant from the Sun.
3 Equulei – ζ Equulei (Zeta Equulei)
Zeta Equulei, or 3 Equulei, is an old giant star belonging to the spectral class K5 III. It is approximately 770 light years distant from the solar system. The star has a visual magnitude of 5.593 and is 949 times more luminous than the Sun.
4 Equulei is another binary star. It is a white main sequence star with an apparent magnitude of 5.94, about 120.4 light years distant.
The star belongs to the spectral class F8V. It is twice as luminous as the Sun. Its estimated age is 2.2 billion years.
HIP 103652, or HR 8038, is a main sequence star of the spectral type A6Vp. It has a visual magnitude of 5.98 and is 235.523 light years distant.
HR 8038 is also a binary star system. It is moving through the galaxy at the speed of 30.3 km/s and will come within 124 light years of the Sun in about 2.1 million years.
6 Equulei is an A-type star still on the main sequence. It belongs to the spectral class A2 Vs and has a visual magnitude of 6.07. It is about 440 light years distant.
6 Equulei is sometimes also known as Gamma Equulei D. This is not because it orbits the Gamma star, but because the two are an optical double separated by 339.13 arc seconds.
HD 200964 is a subgiant of the spectral type K0 IV. It has a visual magnitude of 6.64 and is some 223 light years distant. The star is notable because two large extrasolar planets were discovered in its orbit in July 2010.
The planet closer to the star is almost double the mass of Jupiter, while the more distant planet is slightly less massive than Jupiter. The inner planet has an orbital period of 614 days and the outer one orbits the star every 825 days. This adds up to a 4:3 resonance: every time the bigger planet orbits the star four times, the smaller one orbits the star three times.
DEEP SKY OBJECTS IN EQUULEUS
NGC 7015 is a galaxy with a visual magnitude of 12.4. It is 2.0’x1.8′ in size and about 212 million light years distant.
NGC 7040 is a spiral galaxy with an apparent visual magnitude of 14.0. Its coordinates are 21h 13m 16.5s (right ascension), +08°51’53.2 (declination).
NGC 7046 is a barred spiral galaxy 1.9’x1.4′ in size. It has an apparent visual magnitude of 13.10. The galaxy was discovered by William Herschel in October 1790.
NGC 7045 is not really a deep sky object, but a binary star in Equuleus. It was discovered by John Herschel in July 1827 and included on the list of NGC objects. It has a visual magnitude of 12.0.