Equuleus ( ) is a

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of stars that are visible in the night sky. Its name is

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for "little horse", a

foal A foal is an equine up to one year old; this term is used mainly for horses, but can be used for donkeys. More specific terms are colt for a male foal and filly for a female foal, and are used until the horse is three or four. When the foal i ...

. Located just north of the

celestial equator The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract projectio ...

, it was one of the 48 constellations listed by the 2nd century astronomer

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...

, and remains one of the 88 modern constellations. It is the second smallest of the modern constellations (after

Crux Crux () is a constellation of the southern sky that is centred on four bright stars in a cross-shaped asterism commonly known as the Southern Cross. It lies on the southern end of the Milky Way's visible band. The name ''Crux'' is Latin for c ...

), spanning only 72 square degrees. It is also very faint, having no stars brighter than the fourth magnitude.

Notable features

Stars

The brightest star in Equuleus is

Alpha Equulei Alpha Equulei (α Equulei, abbreviated Alpha Equ, α Equ), officially named Kitalpha , is a star in the constellation of Equuleus. It is a high proper-motion star only 190 light-years away. Nomenclature ''α Equulei'' ( Latinised ...

, traditionally called Kitalpha, a yellow star magnitude 3.9, 186 light-years from Earth. Its traditional name means "the section of the horse". There are few

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

s in Equuleus. Only around 25 are known, most of which are faint.

Gamma Equulei Gamma Equulei, Latinized from γ Equulei, is a double star in the northern constellation of Equuleus. It is located at a distance of around from Earth and is visible to the naked eye with a slightly variable apparent visual magnitude of ...

is an alpha CVn star, ranging between magnitudes 4.58 and 4.77 over a period of around 12½ minutes. It is a white star 115 light-years from Earth, and has an

optical companion In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

of magnitude 6.1,

6 Equulei 6 Equulei is a probable (95% chance) astrometric binary star system in the northern constellation of Equuleus, located 380 light years from the Sun. It is barely visible to the naked eye as a dim, white-hued star with an apparent vis ...

. It is divisible in binoculars. 6 Equulei is an astrometric binary system itself, with an apparent magnitude of 6.07.

R Equulei R Equulei is a class M Mira variable star in the constellation Equuleus Equuleus ( ) is a constellation of stars that are visible in the night sky. Its name is Latin for "little horse", a foal. Located just north of the celestial equ ...

is a

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavelen ...

that ranges between magnitudes 8.0 and 15.7 over nearly 261 days. It has a spectral type of M3e-M4e and has an average B-V colour index of +1.41. Equuleus contains some

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...

s of interest. γ Equ consists of a primary star with a magnitude around 4.7 (slightly variable) and a secondary star of magnitude 11.6, separated by 2

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

Epsilon Equulei Epsilon Equulei, Latinized from ε Equulei, is a star system of apparent magnitude +5.23 in the constellation of Equuleus. It is located 180 light years away from the Solar System, based on its parallax. Star system Two stars make up ...

is a triple star also designated 1 Equulei. The system, 197 light-years away, has a primary of magnitude 5.4 that is itself a binary star; its components are of magnitude 6.0 and 6.3 and have a period of 101 years. The secondary is of magnitude 7.4 and is visible in small telescopes. The components of the primary are becoming closer together and will not be divisible in amateur telescopes beginning in 2015. δ Equ is a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

with an orbital period of 5.7 years, which at one time was the shortest known orbital period for an optical binary. The two components of the system are never more than 0.35 arcseconds apart.

Deep-sky objects

Due to its small size and its distance from the plane of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

, Equuleus contains no notable deep sky objects. Some very faint

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

between magnitudes 13 and 15 include NGC 7015, NGC 7040, NGC 7045 and NGC 7046.

Mythology

Sidney Hall - Urania's Mirror - Pegasus and Equuleus (best currently available version - 2014)

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical co ...

, one myth associates Equuleus with the foal Celeris (meaning "swiftness" or "speed"), who was the offspring or brother of the winged horse

Pegasus Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

. Celeris was given to Castor by

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

. Other myths say that Equuleus is the horse struck from

Poseidon Poseidon (; grc-gre, Ποσειδῶν) was one of the Twelve Olympians in ancient Greek religion and myth, god of the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 In pre-Olympian Bronze Age Greece, he was venerated as a ch ...

's trident, during the contest between him and

Athena Athena or Athene, often given the epithet Pallas, is an ancient Greek goddess associated with wisdom, warfare, and handicraft who was later syncretized with the Roman goddess Minerva. Athena was regarded as the patron and protectress of ...

when deciding which would be the superior. Because this section of stars rises before

, it is often called Equus Primus, or the First Horse. Equuleus is also linked to the story of Philyra and

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

. Created by

Hipparchus Hipparchus (; el, Ἵππαρχος, ''Hipparkhos''; BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equi ...

and included by

, it abuts Pegasus; unlike the larger horse it is depicted as a horse's head alone.

Equivalents

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categorized in the twe ...

, the stars that correspond to Equuleus are located within the Black Tortoise of the North (北方玄武, ''Běi Fāng Xuán Wǔ'').AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 15 日
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References

* Burnham, Robert (1978). ''Burnham's Celestial Handbook: An observer's guide to the universe beyond the solar system'', vol 2. Dover Publications * Hoffleit+ (1991) ''V/50 The Bright Star Catalogue'', 5th revised ed, Yale University Observatory
Strasbourg astronomical Data Center
* * Ian Ridpath & Wil Tirion (2007). ''Stars and Planets Guide'', Collins, London. . Princeton University Press, Princeton. .

External links

The Deep Photographic Guide to the Constellations: Equuleus

Warburg Institute Iconographic Database (medieval and early modern images of Equuleus)
{{DEFAULTSORT:Equuleus Constellation Constellations Northern constellations Constellations listed by Ptolemy