Equuleus (Latin for horse-let (i.e. a foal)) is the second smallest of the 88 modern constellations, only Crux being smaller.

Despite its smallness and lack of bright stars (none are brighter than fourth magnitude), it was also one of Ptolemy's 48 constellations.

Notable features

Equleuus is the second smallest constellation, at 72 square degrees. The only constellation that is smaller is Crux. It is not a particularly conspicuous constellation; its brightest star is Kitalpha (α Equ), at magnitude 3.92m.

There are few variable stars in Equuleus. Only around 25 are known, most of which are obscure. γ Equ is an alpha CVn star , ranging between magnitudes 4.58m and 4.77m over a period of around 12½ minutes. R Equ is a Mira variable that ranges between magnitudes 8.0m and 15.7m over nearly 261 days.

Equuleus contains some double stars of interest. γ Equ consists of a primary star with a magnitude around 4.7m (slightly variable) and a secondary star of magnitude 11.6, separated by 2 arcseconds. ε Equ consists of four components. The brightest three are of magnitudes 6.0m, 6.3m, and 7.2m. δ Equ is a binary star 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.

Notable deep sky objects

Due to its small size and its distance from the plane of the Milky Way, Equuleus contains no notable deep sky objects.

Mythology

Equuleus is associated with the foal Celaris , who was the brother of the winged horse Pegasus. Celaris was given to Castor by Mercury.

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