September’s arrived, and that means stargazers have a final few weeks to see the long, starry arc of the Milky Way and all its attendant splendor. The rich constellations of Scorpius and Sagittarius are moving westward, but the lengthening nights keep these stars accessible for a little longer, at least for observers in the northern hemisphere. Also in September, a string of bright planets from Venus in the west to Mars in the southeast remains visible to liven up the sky. Here’s what to see in the night sky this month…