As Orion sinks in the W and the Plough wheels overhead at nightfall today, the signature constellation of our spring sky stands high on the meridian. Leo, the celestial lion since antiquity, squats and faces W with his head and mane represented by the arc of stars we dub the Sickle. Leo's leading star, Regulus, marks the Sickle's handle or, alternatively, Leo's heart and shines at magnitude 1.4 from a distance of 77 light years (ly). Look for it near the Moon on Wednesday.
The name Regulus or "little king" was given by Copernicus in recognition of its ancient role as one of four royal stars that guarded the four quarters of the sky or the year. The others are Aldebaran, Antares and Fomalhaut.
In its apparent annual journey around our sky, the Sun passes closer to Regulus than any other comparable star, with the conjunction occurring this year on 23 August when the Sun's northern edge misses the star by a mere 12 arcminutes. In fact the Sun crosses the constellation between 11 August and 18 September, even though astrologers claim that the Sun is "in Leo" between about 23 July and 23 August.
Leo's second star, magnitude 2.1 Denebola at 36 ly, marks the lion's tail. Look more than 20° below and to the left of Denebola for the conspicuous planet Saturn, and further in the same direction for Spica, the leading star in Virgo, the next zodiacal constellation after Leo.
Algieba in the Sickle is a striking double star with component stars 4.6 arcseconds apart. Each is a giant, much larger and brighter than our Sun, and the brighter one may have at least one planet that is significantly larger than Jupiter. Don't be confused by the fact that Algieba has another more distant neighbour, the star 40 Leonis which lies less than a Moon's breadth away to its south.
Eta, between Algieba and Regulus, is a white supergiant some 2,000 ly distant and so luminous that it would outshine Venus if placed at Regulus's range. In contrast, it would take a thousand stars like the red dwarf Wolf 359 just to rival the light output of our Sun. This tiny star shines at the 13th magnitude from a distance of 7.8 ly, so don't expect to see it without a large telescope even though only four stars in the entire sky lie closer to the Sun, and three of these are forever below the horizon as seen from Britain.
R Leonis, a red slowly pulsating variable star of the Mira type, spends most of its time at telescopic brightness but is currently visible through binoculars below a stellar pair 2° above and to the left of Omicron. Finally, the spiral galaxies M65 and M66 stand side by side and midway between Iota and Theta in Leo's hindquarters. At mag 9 and 35 million ly away, they may just be glimpsed through binoculars but are easy through a telescope.