Equuleus

This tiny constellation of faint stars has been known as the 'foal' (or literally 'little horse') for more than two thosand years. There are several varying stories of its origins, but perhaps the most likely is the suggestion that it represents Celeris, the foal of Pegasus. Equuleus lies directly to the west of Pegasus in the sky, so a connection between the two ancient horse-constellations seems perfectly plausible.

Equuleus is the smallest constellation visible from the northern hemisphere, and indeed would be the smallest in the entire sky but for the southern constellation of Crux. Equuleus' angular area is just 72 square degrees, but Crux is marginally smaller at 68 square degrees.

Equuleus in the Sky

Equuleus can be located in the sky using the Square of Pegasus as a starting point. Extending out from the southwest corner of the Great Square is a triangle of stars representing the head of Pegasus, and that 'head' points directly towards Equuleus. The small constellation falls between the tip of Pegasus' nose (the star Enif) and bright Altair, in the head of Aquila the Eagle to the west.

Though it is surrounded by recongisable constellations, the general faintness of Equuleus' stars can make it difficult to spot. In the night sky, it tends to be most easily seen as a long, narrow, southward-pointing triangle of dim stars. Gamma and Delta Equulei form the triangle's base, and it points southward like an arrowhead towards the marginally brighter star Kitalpha.

Stars

Equuleus' small size, combined with the fact that it encompasses a region of sky well outside the main plane of the Milky Way, means that it contains no bright stars and few other objects of note. The constellation contains only nine stars numbered by Flamsteed (compared with a more typical number of eighty-nine such stars in neighbouring Pegasus).

Alpha Equulei is the brightest of Equuleus' stars, and the only one to have a traditional common name: Kitalpha (a name that translates rather prosaically as 'part of the horse'). With a visual magnitude of +3.9, Kitalpha is hardly a truly bright star in any absolute sense (there are nearly five hundred brighter stars in the sky). Kitalpha is in fact a rather luminous yellow subgiant, but its distance of 186 light years from the Solar System makes it faint in the skies of Earth. It is a binary star, with a small blue companion orbiting the main yellow star.

Though conventionally the Beta star of a constellation is its second-brightest, Equuleus certainly does not follow that pattern. Beta Equulei is a dim white star in the eastern parts of the constellation, so faint that it is on the edge of naked-eye visibility.

The other two prominent stars in the constellation are Gamma and Delta Equulei, lying close together in the sky, northward of Kitalpha. Both of these stars are rather closer to the Sun than Kitalpha, but also less intrinsically luminous, and so appear fainter to an observer on Earth. Delta Equulei is notable as being somewhat similar to the Sun; some sixty light years distant (about a third of the distance to Kitalpha), it is only a little hotter and larger.

Deep Sky Objects

This sparse area of sky is almost devoid of deep sky objects, but on Equuleus' southern border with Aquarius lies a dense group of galaxies. This group contains about a hundred individual galaxies filling an area of sky larger than the disc of the Moon, but the group as a whole is enormously distant (about 175 million light years from the Milky Way) and hence extremely faint. Most prominent among these (but with an apparent magnitude of just +13.1) is a sprawling barred spiral galaxy designated NGC 7046.