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When is fall? The fall or autumn equinox on Sept. 22 signals the beginning of a new astronomical season, but stargazers can already see it coming.
As autumn approaches, one of the night sky's most familiar star patterns -- the Big Dipper (known as the Plough in the U.K. and Ireland) -- remains a signpost. Visible on clear September evenings, this seven-star asterism (a shape of stars, not an official constellation) moves into a noticeably low position in the northern sky after sunset.
Step outside after sunset on any clear night this September and turn your gaze toward the north-northwest horizon. The Big Dipper will be hanging low in the sky, its bowl tilted towards due north.
It is always thus. The phrase "spring up, fall down" is used by stargazers to remember how the Big Dipper rides high in the evening during springtime, then sinks low in the evening during fall. However, it always orients towards north.
You'll need an unobstructed northern horizon, though you should be able to find the stars of the Big Dipper an hour or two after dark. Notice its seven stars, from its bowl to the tip of the handle. See how its handle curves, then go in an "arc to Arcturus" to a bright star slightly lower on the horizon. Arcturus is the brightest star in the constellation Boötes.
Return to the four stars in the Big Dipper's bowl. Trace a line from the bowl's two outer stars upward and you'll find Polaris, the North Star -- where Earth's northern axis points. This is the star that the Big Dipper revolves around. Now come down from Polaris to the horizon -- that's due north. Now go beyond Polaris and you'll find the W-shaped constellation Cassiopeia, which is always opposite the Big Dipper.
As the Big Dipper gets lower on the horizon, Cassiopeia gets higher, with both completing one rotation of Polaris every 24 hours.
As the fall equinox approaches on Sept. 22 -- as hinted at by the position of the Big Dipper after sunset -- there's plenty to see in the night sky. For early risers, there's the remains of a planet parade. Venus shines brightly near the eastern horizon before dawn, while Jupiter and Saturn are higher in the sky. Saturn's bright opposition on Sept. 21 means it is exceptionally bright -- if you can find a small telescope, you'll see its fabulous rings. Uranus and Neptune require a small telescopes to see, but their presence makes this the last five-planet line-up until 2028.
Further ahead, there could be something special coming when Comet Lemmon (C/2025 A6), once mistaken for an asteroid, is forecast to brighten in mid-October. Its closest approach on Oct. 20-21 coincides with dark new moon skies and the peak of the Orionid meteor shower.