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    Articles > April 2000
 
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Secrets of the Night Sky

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  In the Neighborhood of the "Little King"
Regulus, the brightest star in the constellation Leo, lies at the base of an easy to find figure of stars (or asterism) known as "The Sickle." These stars form the head and chest of a reclining westward-facing lion. Regulus means "Little King" in Latin but has at times also been known as Cor Leonis, "The Heart of the Lion." Use the sky map to find "The Sickle." It looks like a backward question mark high up in the southern sky. Can you see the pattern of six stars?

The Constellation of Leo
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A few degrees north of Regulus (on the sickle) lies the seemingly inconspicuous star known as Eta Leonis. It is in fact a hot white supergiant star over 15,000 times more luminous than our Sun. Eta Leonis appears fainter than Regulus because it is nearly 30 times further away from us than Regulus. If Eta Leonis were at the same distance as Regulus (77 light years) it would appear almost as bright as Venus and outshine every other star in the night sky. If it were the same distance as Sirius (8.6 light years) it would appear 50 times brighter than Venus and be visible even in the daytime!

Near the paw of the great lion, about 5 west of Regulus, lies another inconspicuous star that shines bright for only a few days each year. The star is known as R Leonis, a red giant variable star that changes brightness as it undergoes a periodic expansion and contraction in size. It steadily brightens and fades between about magnitudes 5 and 10 over a period of 312 days.

This year R Leonis is expected to reach maximum brightness around late April or early May. Use binoculars to observe its distinct reddish glow over a period of a few weeks. R Leonis may even become visible to the unaided eye.

The Planets in April
Jupiter, Saturn and Mars are visible close together and very low in the western sky. The crescent Moon will join them on 6 April. Sky watchers in Japan and Australia will see the Moon cross in front of the Hyades star cluster on the evening of 8 April. Clear skies until next month!


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