Gamma Arietis
AKA: Mesarthim or STF 180. Position: 01 hr 53.5 min +19 deg 18 min.
Due south at 22.16 (GMT) on 15 November 2019
Image Credit: Les Brand (HAS)
To find this star, look for the Square of Pegasus which is in the south-west around 10 pm. Then follow the line formed by the bottom of the square eastwards. You will see two fairly bright stars close together, Alpha Arietis and Beta Arietis, and to the west (“right”) of this pair and slightly lower is the dimmer Gamma Arietis. The two stars are practically equal – the primary is 4.52 and the secondary 4.58 – and they are both white. With a separation of 7.5″, they are fairly close together and would benefit from a fairly high magnification, but they should be separated with a small telescope thanks to their equal brightness. While the stars are white (they are both stellar class A0), some observers have detected a hint of colour in the secondary, see what you think. Despite the relative tightness of this double, this was one of the first double stars to be seen through a telescope, recorded by the polymath Robert Hooke in 1664. Both the position angle and separation have changed since their data were recorded by William Herschel in 1779, it was a much easier target for Herschel with a separation of 10.2″, and it is a true binary star.