Sky Watch: September 2018

Best Night Sky Events of September 2018

By Bob Berman
September 9, 2018
An Autumn Sunset
Abigail Lockey

Welcome to your September 2018 Sky Watch. We’ll help you spot the best night sky events of September, including four bright planets, several beautiful Moon pairings, and a glowing green comet! Also, note the upcoming autumnal equinox!

Sky Watch September 2018

by Bob Berman, as featured in The 2018 Old Farmer’s Almanac

What’s up in the September night sky? Here are the highlights:

Bright Planets

In the Northern Hemisphere, four planets are still all highly visible in the night sky. They are lower in the sky and starting to dim, so spot these bright planets on the next clear night in September!

  • Venus, brilliant in the western sky, reaches its greatest brilliancy at magnitude –4.8 in the latter half of this month though it has gotten much lower and nearer the horizon. Look for Venus in the western sky after sunset as our “Evening Star.”
  • Jupiter shines bright above Venus after sunset, with their separation narrowing each evening. The Red Planet fades to magnitude –1.6 at midmonth, matching Sirius, the night’s brightest true star. 
  • Mars and Saturn light up the southern sky at nightfall. Mars, so dazzling over the summer, starts to dim this month as Earth moves ahead of Mars in orbit. 
  • Mercury is bright at magnitude –1 in the predawn east from the 1st to the 6th, when it meets Leo’s blue star, Regulus.

See planet rise and set times for your location here.

Moon Pairings

  • Watch the Moon pass to the right of Jupiter on the 13th, to the left of bright Saturn on the 17th, and then above Mars on the 19th.

Glowing Green Comet

Credit: NASA

Sky watchers will get views of glowing green comet 21P/Giacobini-Zinner during most of September—with only binoculars or a small backyard telescope. It’s coming closest to Earth on September 9–10 than it has in 72 years. Look high up in the skies after midnight on Sunday or before dawn on Monday if you want to see a comet with a great tail and bright head. Learn more about viewing comet 21P—plus, comet facts.

Autumnal Equinox

Click here for a free sky map to navigate the night sky!


The Old Farmer's Almanac

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