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The Sun changes hemispheres today. It crosses the equator from north to south. That ushers in autumn here in the northern hemisphere, and spring in the south.
There’s also a division of hemispheres in the evening sky — a division that also marks the changing seasons. The western half of the sky features some of the most prominent stars and constellations of summer, while the eastern sky features the stars of autumn.
As night falls, look low in the south and southwest for two bright markers of summer — the teapot of Sagittarius and the curved body of Scorpius, the scorpion. And off to the left of Sagittarius, in the southeastern sky, look for Capricornus and Aquarius, two denizens of autumn. They’re fainter than the summer stars, though, so they’re tougher to pick out.
Over the next few weeks, Scorpius and then Sagittarius will drop out of the evening sky, but their autumn counterparts will climb higher.
It’s all caused by our changing perspective on the stars. Every star rises and sets four minutes earlier each day. So that gives us new stars to admire with each season — and a season for each star.
One symbol of summer straddles the eastern and western halves of the sky tonight: the Summer Triangle. And that seems fitting, since the name is a bit off. The triangle is in good view in the evening skies of summer, but it remains in the evening through the next change in seasons — when autumn gives way to the cold nights of winter.