Equuleus is the second smallest constellation, and despite having no bright stars was one of Ptolemy’s original 48 constellations and is recognized by the IAU as one of the 88 modern constellations. Covering only 72 square degrees and possessing 3 main stars, Equuleus harbors on 10 stars with Bayer/Flamsteed designations. It is bordered by the constellations of Aquarius, Delphinus and Pegasus. Equuleus is visible to all observers at latitudes between +90° and ?80° and is best seen at culmination during the month of September.
As for mythology, Equuleus the “Little Horse”, has its fair share of legend. It is mainly associated with the foal Celeris, the offspring of the mighty winged horse, Pegasus. Celeris was a gift given to Castor by the messenger god, Mercury. As legend goes, Equuleus is the horse struck from Neptune’s trident, during the contest between him and Athena when deciding which would be the superior. Because this section of stars rises before Pegasus, it is often called Equus Primus, or the First Horse. Equuleus is also linked to the story of Philyra and Saturn. The parents of Chiron, who may represent the constellation of Centaurus.
Now, let’s roam around the skies of Equuleus with binoculars, starting with Alpha, the “a” shape on our map. Alpha Equulei proper name is Kitalpha, which means “part of the horse”. What it is… is a unique spectroscopic binary star. At a distance of about 186 light years from Earth, Kitalpha shines away merrily about 75 times brighter than our Sun. But the class G primary giant star is dying – its helium core contract. Nearby is its white dwarf companion. Very nearby. These two stars are so close together that the stellar spectral class is mixed, G + A, with two spectra present at the same time. What’s happening? The dwarf companion star is unevolved hydrogen-fuser. One day the mass transfer between the two should lead to some very interesting conclusions!
Point your binoculars towards Delta – the figure “8” shape on our map. Delta Equulei goes by the name Pherasauval, which loosely means “the first horse”. Pherasauval is a binary star system with a class G0 star and a class F5 one. What makes it a real curiosity is because its mass can’t quite be determine – and because we’re looking at a pair of stars that are pretty much the same as our own Sun at a distance of 60 light years from our solar system. Take a look through a telescope to split this pair apart and dream of what it would be like to be a planet where two suns were always in the sky!
Now take a look a Gamma Equulei – the “Y” shape on our map. This is an easy double star to split with binoculars (A and D), but use a telescope because this is a multiple star system! The primary star (A) is magnitude 4.7 and the B star (secondary) is a disparate magnitude 11. A bit further away, look for an optical 12th magnitude companion and a 6th magnitude D star as well!
While there are almost no deep sky objects bright enough to be hunted down with most amateur telescopes, larger aperture telescopes might be interested in trying their luck with 13th magnitude NGC 7015 (RA 21:05.7 Dec +11:25). Also known as Stephan IX, this faint lenticular galaxy was was catalogued for the first time in 1888 in the New General Catalogs by the Danish astronomer John Dreyer.
If you’re really challenged, try your hand at a small group of galaxies head by UGC 11697 (RA 21h 12m 06.0s Dec +11 38′ 00″). At magnitude 15 and about 1 arc minute in size, you’re going to have fun spotting it!