If you’re ready for a taste of summer, look no farther than the dawn sky. The constellations in view at first light are just what you’ll see as night falls in July and August. Scorpius is low in the south, with Sagittarius in the southeast. The Big Dipper hangs from its handle in the northwest. And the Summer Triangle — the stars Vega, Deneb, and Altair — stands high in the east.
As Earth orbits the Sun, our viewing angle on the stars changes. As a result, each star rises about four minutes earlier each night. So a star that rises at dawn now, will rise eight hours earlier in July, 10 hours earlier in August, and 12 hours earlier in September.
Now you might think this all means that we’d see the current morning configuration 12 hours earlier in the night during September — half a year from now. And you’d be partially right. The same configuration of stars will be in the sky at that hour. But the Sun sets later then, so it’s still daylight when the stars stand in their current dawn positions. So by sunset then, Scorpius and the others will have rotated farther to the west. That means the best time to see this setup in the early evening sky is a month or two earlier — July and August.
That all sounds a bit confusing, but trust us: The stars have been following that pattern for a long time — moving the same stars we see in the dawn sky now into the evening sky during the short nights of summer.