Constellations: Equuleus 'the Foal' Content from the guide to life, the universe and everything

Constellations: Equuleus 'the Foal'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
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Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium
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Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Name:Equuleus (Latin: 'the Foal')
Short form:Equ
Area:72 sq deg
Co-ordinates1:Right Ascension 21h, Declination +10°

The constellation of Equuleus the Foal is in the Northern Hemisphere and at only 72 square degrees it is the second smallest by area. It is best seen in the late summer-early autumn months in the south at around midnight. Its three primary stars form an acute triangle pointing north-south. Although its brightest stars are only fourth magnitude it is easily located between Pegasus on its eastern border and Delphinus on its western side. All three sit on the northern border of Aquarius. The easiest way to locate this constellation is to first find the much more prominent Delphinus and then look to its south-eastern side the distance of about the width of two full moons. There are located three rather dim stars in a roughly triangular shape with its northern base over its southern apex.

Mythology and History

Equuleus is the 'foal' or 'little horse' Celeris, the brother of the winged horse Pegasus. He was reputed to have been given by Mercury (the messenger of the Gods), to Castor, the mortal one of the heavenly twins who was skilled in pugilism and horsemanship. The creation of the constellation has been attributed to the greatest of the ancient Greek astronomers, Hipparchos. The Foal was known to Ptolemy who listed it as one of his 48 constellations, but referred to it only as the upper part of an animal figure. To later astronomers it was Equus Primus or Equus Prior, which referred to it preceding the rising and setting of Pegasus in the nightly procession across the sky. The 1551 Latin translation of the Almagest calls it Praecisio Equi.


Northern observers will see the primary stars of Equuleus as a rather dim triangle with the brightest of these only +3.92 magnitude. Alpha Equulei is sometimes known by the name Kitalpha, which to early Arabian astronomers represented the whole asterism. It is a spectroscopic binary and forms the southern point of the triangle. Gamma and delta create the northern base. Both are binary stars which can be separated in large aperture telescopes. Beta is another binary system.

Star Table

StarDesignationName or Catalogue NoBrightness (m)Distance
(light years)
α Equalpha EquuleiKitalpha+3.92186Binary
δ Equdelta EquuleiHIP 104858+4.4660Binary
γ Equgamma EquuleiHIP 104521+4.68115Binary
β Equbeta EquuleiHIP 105570+5.15360Binary

Deep Sky

Equuleus' position in the sky is a relatively barren area as it is divorced from the mainstream of the Milky Way. Consequently there are no star clusters or nebulae that might have attracted Charles Messier to give them a number, or that are easily seen with amateur equipment. There are several face-on galaxies: NGC 7015, NGC 7040 and NGC 7046, but none are brighter than 13th magnitude, making them available only to larger telescopes.

Extrasolar Planets

The orange subgiant star HD 200964 has two gas giants in orbit, at 1.6 AU and 1.95 AU. One exoplanet, WASP-90 b, was discovered by the transit method in 2013. HAT-P-65 b is a hot gas giant orbiting its star in just 2.6 Earth days.

Equuidae in Nature

The horse family Equuidae includes the modern horse and other living sub species Ass, Donkey and Zebra2. Females give birth to one foal usually, but occasionally twins are born. Their gestation period lasts up to 360 days, although mares have the ability to delay birth if they are not happy with their surroundings. Foals are able to stand and walk within an hour of their birth. They are weaned after six to eight months.

Equuleus in Modern Culture

A production of Peter Shaffer's play Equus ran from 27 February until June 2007 at the Gielgud Theatre in London's West End. It was notable for the debut of Daniel Radcliffe who had previously starred in the title role of the series of 'Harry Potter' films. The play is remarkable for one scene during which Daniel is required to play naked. This was a notable departure from his film appearances in which it was only his magic wand that he was expected to wave.

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2And other such creatures when horsing around takes place.

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