Double Star of the Month:
54 Leonis
AKA: STF 1487. Position: 10 hrs 55 min 36.8 sec 24 degrees 44 min 59 sec
Due south at 22:20 (BST) on 15 April 2021.
Image credit: Jeremy Perez (http://www.perezmedia.net/beltofvenus)
Used with permission
This month we have a double which is a bit tighter than my usual easy doubles (be warned the doubles of the month are becoming more difficult!). 54 Leonis is above the back of the Lion, about halfway between Regulus and Denebola, on the same level as the middle of the hook of the Sickle asterism. It is fairly faint at magnitude 4.5 and you will probably have to use your finderscope to locate it. The companion is magnitude 6.3 and the separation is 6.8 arcseconds so you will need to use a fairly high magnification, perhaps 80x to 100x. The main star is spectral class A0 and the secondary is A2, which suggests that they are both white. However I see the main star as yellowish-white and some observers even see it as yellow. Similarly I see the secondary as blue or perhaps red; this is often seen as blue, probably because of the contrast with a yellowish star. The two stars are about 2.5 times the mass of the Sun and they are rapid rotators (see Star of the Month for March 2021) so they are both egg-shaped. Given their similarities it is not surprising that they are a true binary system, which is about 330 light years away from us. The main star is 411 million years old or almost half of its lifetime on the main sequence. William Herschel observed it on 21 February 1777, describing it as considerably unequal (in brightness), brilliant white and ash-coloured. However he was not the first astronomer to discover its duplicity, since it had been observed by the German-Moravian Jesuit astronomer Christian Mayer about the same time.
If you observe 54 Leonis in April 2021, you get a bonus in the shape of the dwarf planet Vesta. Vesta is below 54 Leonis (and slightly to the right or west) on the same level as the bright double Gamma Leonis or Algieba (see Double Star of the Month for March 2020). Vesta will be about magnitude 6.1 and just to the left (or east) of the star m Leonis which is magnitude 5.5, you should be able to get them in the same field of view.