06 October 2017 by Brian Jones
For autumn, we turn our attention to the tiny constellation Equuleus (little horse), which takes the form of a small trapezium of faint stars visible immediately to the west of the much larger constellation Pegasus. Equuleus can be tracked down fairly easily provided the sky is dark, clear and moonless. If you have any difficulty, then binoculars will help.
Get your bearings
Such is the position of Equuleus that it can be seen from anywhere north of latitude 77°S, making it accessible to ramblers and trekkers located in almost any inhabited part of the world. To find it, first of all seek out the large pattern of stars in Pegasus known as the Great Square of Pegasus, formed from the four bright stars Sirrah, Scheat, Markab and Algenib.
For those of you observing from mid-northern latitudes, this pattern of stars will be visible high in the southern sky, although from mid-southern latitudes you will need to look a short way above the northern horizon (and bear in mind that it will appear inverted in relation to how it is depicted on this chart). Now follow an imaginary line from Sirrah diagonally across the Square of Pegasus, through Markab and on roughly as far again, until you reach the relatively bright star Enif, from where the small but distinctive pattern of Equuleus is easily tracked down.
Bright and beautiful
The brightest star in Equuleus is magnitude 3.92 Kitalpha, its name being aptly derived from the Arabic Qit’at al-Faras – meaning ‘the section of the horse’. You can read more about star names here. Kitalpha shines from a distance of around 190 light years, which means the light we are seeing today from this star actually set off towards us during the reign of George IV.
The second brightest star in the group is Delta Equulei, which lies much closer to us. The light from this magnitude 4.47 star having taken just 60 years to reach our planet. Much further away than either of these is faint Beta Equulei which, shining at magnitude 5.16 from a distance of 330 light years, lies at roughly twice the distance of magnitude 5.30 Epsilon Equulei, the light from which reaches us from 175 light years away. You can read more about magnitudes on Starlight Nights.
The magnitude 4.70 white giant star Gamma Equulei completes the main outline of Equuleus. The light from Gamma set off towards us 118 years ago, just before the end of the reign of Queen Victoria. A closer look at Gamma will reveal that it forms a wide double with the magnitude 6.07 star 6 Equulei. However, the relationship between these two stars is nothing more than a line-of-sight effect, 6 Equulei being located at a distance of around 440 light years, nearly four times that of Gamma. You can read more about star colours on Starlight Nights.
Provided the sky is exceptionally dark, clear and moonless, you may just be able to pick out the faint glow from 6 Equulei and resolve this pair with the naked eye, although you will probably need the help of binoculars to bring out both stars quite well.
So, take the time to look upwards and seek out tiny Equuleus as he trots across the star-filled heavens. Happy stargazing!
Walk’s resident stargazer, Brian Jones, has recently begun co-editing the popular Yearbook of Astronomy (formerly known as Patrick Moore’s Yearbook of Astronomy). For more stargazing inspiration, follow Brian on Twitter @StarsBrian.
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