The frosty stars of winter continue to dominate the evening sky. Yet there’s already a hint of spring in the nighttime air. Leo, the lion, one of the best-known constellations of spring, is in good view by around 9 o’clock, and climbs high across the south later on. Look for its bright heart, the star Regulus, with its head to the upper left of Regulus and the body and tail to its lower left.
The constellations change with the seasons because of Earth’s orbit around the Sun.
In relation to the “fixed” stars, Earth rotates on its axis once every 23 hours and 56 minutes. In other words, any given star returns to the same position in the sky 23 hours and 56 minutes later from one day to the next.
During that time, Earth moves in its orbit around the Sun. Because of that, the Sun returns to the same position in the sky every 24 hours — four minutes longer than the cycle for the more-distant stars. So except for the ones that are so close to the Pole Star that they’re always in the sky, the stars rise and set about four minutes earlier each day.
That’s not much of a difference from one night to the next. Over a month, though, it adds up to two full hours. So stars that are low in the east at 9 o’clock tonight — like those of Leo — will stand high in the south at the same hour a couple of months from now. That gives each star and constellation a season of its own — with Leo ready to stand high in the evening skies of spring.
Script by Damond Benningfield, Copyright 2013
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