Constellations of the Month: September – Equuleus:
We continue September with the next constellation of the month, Equuleus, the “Little Horse” or “Foal.”

Equuleus constellation map courtesy of Openverse

Equuleus, The “Little Horse” or “Foal” – The Equuleus constellation is an equatorial constellation, located in the northern and southern hemispheres, symbolizing the “little horse” or “foal.”  Its name translates to “little horse” or “foal” in Latin. This foal constellation is linked to various Greek myths, particularly the tale of Hippe, the daughter of the centaur Chiron and the nymph Chariclo. Although the originator of the constellation remains unknown, Equuleus was first documented by the Greek astronomer Claudius Ptolemy in the 2nd century CE, alongside other Greek constellations. Equuleus is characterized as a small and faint constellation, containing few significant deep sky objects and lacking stars brighter than fourth magnitude. It is occasionally referred to as Equus Primus, or the First Horse, due to its rising just before the Pegasus constellation. The larger Pegasus symbolizes the winged horse in Greek mythology. Equuleus is not very hard to find but can be tough to spot in areas with light pollution due to its faint stars. It is located between Enif, the brightest star in Pegasus, and Altair, a bright star in Aquila. Delta and Gamma Equulei are on the line between Enif and Altair, while Kitalpha and Beta Equulei are south of this line.

SDSS NGC 7046 courtesy of Openverse

Key points regarding Equuleus:

• Meaning: The term “Equuleus” translates to the “Little Horse” or “Foal” in Latin. In Greek mythology, this constellation lacks any stars that are brighter than magnitude 3.00 or situated within 10 parsecs (32.6 light years) from Earth. The constellation’s brightest star is Kitalpha, also known as Alpha Equulei, which has an apparent magnitude of 3.919. The closest star, HD 200779, is located 48.41 light years away from Earth. Within Equuleus, there are three stars that host known exoplanets. HD 200964, classified as spectral class K0IV, has two planets, whereas both WASP-90 (F6) and HAT-P-65 (G2) each have one transiting planet. The constellation features one star that has been formally named. The name recognized by the International Astronomical Union (IAU) is Kitalpha (Alpha Equulei A). Equuleus does not include any Messier objects, nor are there any meteor showers linked to this constellation. It is part of the Heavenly Waters constellation family, which also includes Carina, Columba, Delphinus, Eridanus, Piscis Austrinus, Puppis, Pyxis, and Vela.
• Notable stars: Alpha Equulei is a binary star system composed of Kitalpha, a yellow giant about 2.3 times the Sun’s mass and much brighter, and another white star. Kitalpha is located around 190 light years away with a visual magnitude of 3.919. Delta Equulei, the second brightest star in the constellation, is a binary system 59.4 light years away, with a visual magnitude of 4.47, and both stars are slightly larger and more massive than the Sun. Gamma Equulei, a double star about 118 light years from Earth, is known for its brightness changes and has a faint companion. Beta Equulei is a single white main sequence star, larger and more luminous than the Sun, located 133 light years away with a visual magnitude of 5.19. Epsilon Equulei is a multiple star system with four stars, about 180 light years away, with components slightly more massive than the Sun.
• Other features: NGC 7015 is a spiral galaxy with a visual magnitude of 13.25 and a size of 1.9 x 1.6′, located 203.2 million light years away. It was discovered by Édouard Stephan in 1878. NGC 7040 is another spiral galaxy, with an apparent magnitude of 14.9, lying 257.5 million light years away, discovered by Mark Harrington in 1882. NGC 7046 is a barred spiral galaxy with a magnitude of 13.75 and a size of 1.9 x 1.3′, located 176 million light years away, discovered by William Herschel in 1790. NGC 7045 is a binary star with a visual magnitude of 12.0, discovered by John Herschel in 1827.
• Mythology: Equuleus, known as the little horse constellation, is typically linked to Hippe, the daughter of the centaur Chiron in Greek mythology. According to Greek tradition, Hippe was seduced by Aeolus and became pregnant. Ashamed to reveal this to her father, she concealed her pregnancy from Chiron. She fled to the mountains where she remained until she gave birth to her child, whom she named Melanippe. When Chiron sought out Hippe, she prayed to the gods for protection from being found, and they transformed her into a mare. In one rendition of the story, it was the goddess Artemis who placed Hippe among the stars. She appears to be evading Chiron, with only her head visible behind Pegasus. (Chiron is symbolized by the constellation Centaurus.) The Equuleus constellation is also occasionally associated with Celeris, a foal gifted to Castor by Mercury. The name Celeris translates to “speed” or “swiftness.” This foal was either the sibling or descendant of Pegasus, the renowned winged horse, which is depicted in the larger adjacent constellation.
• Visibility: Equuleus is the 87^th largest constellation (2^nd smallest constellation in the night sky, following Crux, the Southern Cross). It covers an area of merely 72 square degrees. This constellation is situated in the fourth quadrant of the northern hemisphere (NQ4) and is observable at latitudes ranging from +90° to -80°. Its neighboring constellations include Aquarius, Delphinus, and Pegasus. The name Equuleus is pronounced /ɪˈkwuːliəs/. In English, it is referred to as the Little Horse or Foal. The genitive form of Equuleus, which is utilized in star nomenclature, is Equulei (pronunciation: /ɪˈkwuːliaɪ/). The three-letter abbreviation, which was officially adopted by the International Astronomical Union (IAU) in 1922, is Equ.

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Constellations:

Equuleus courtesy of Openverse

Constellations of the Month:
September – Equuleus

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