The Stars of Spring
As winter fades and spring arrives the stars in our evening sky change and new stars, not seen over the winter, make a reappearance.
Two of those stars are Arcturus, in the constellation of Bootes, and Spica, in Virgo, both of which will become early evening objects in April (in early March Spica doesn’t rise until 2130, three hours after sunset).
Spica, or the “ear of wheat” is held by Virgo the Virgin, and its presence in the evening sky has long been used by ancient astronomers as an indication that spring is coming.
To find these stars start with the curved handle of the Plough and continue that arc down to Arcturus. Spica is the same distance again beyond Arcturus. You can use the common mnemonic: “Arc to Arcturus and spike down to Spica”.
These stars should be easy to spot as they’re very bright, Arcturus being the fourth brightest star in the night sky at -0.04 magnitude (only Sirius, Canopus and Alpha Centauri are brighter, and only one of these – Sirius – is visible from the UK), and Spica is the 15th brightest at +1.04 magnitude.
Arcturus is so bright for two reasons: (1) is it intrinsically quite bright, being an orange giant star (the Sun would fit inside Arcturus 17000 times), and (2) it is quite close to us, being only 37 light years away.
Spica, by comparison, is intrinsically even brighter (it too is a giant star, but it is a super-hot blue-white giant compared to the rather cooler orange Arcturus), but it is a little smaller (“only” 400 Suns would fill it) and much further away, around 260 light years distant.