(Looking for last month’s ‘Night Sky’? Find it at this link…)
September marks a change of seasons as the Sun crosses the celestial equator heading south and the Full Harvest Moon arrives. All five bright planets make an appearance this month. Saturn and Neptune reach opposition, Mercury makes its best appearance in the morning sky for 2024, and Mars lies among the bright stars of Gemini as it brightens and grows bigger. And though it’s not visible until at least month’s end, the promising Comet C/2023 (A3) Tshuchinshan-ATLAS reaches perihelion on its way (hopefully) to a great show in October. Here’s what to see in the night sky this month…
1-15 September. Over the next two weeks, northern-hemisphere observers with very dark sky can see the zodiacal light in the east about 90-120 minutes before sunrise. This whitish wedge of light appears to thrust upward from the horizon. The zodiacal light is simply sunlight reflected off tiny dust particles in the inner solar system.
3 Sept. New Moon, 01:56 UT
5 Sept. A slender crescent Moon emerges in the evening sky and tonight lies less than 7º from Venus in the west-southwest after sunset.
5 Sept. Mars lies a little less than one degree south of the star cluster M35 in Gemini. Grab a pair of binoculars or a little telescope to capture both in the same field of view high in the eastern morning sky before dawn.
5 Sept. Mercury reaches greatest western elongation 18º from the Sun. It appears low in the east-northeast morning twilight sky for the first three weeks of September and makes its best morning apparition for northern observers in 2024. The planet reaches an impressive brightness of magnitude -1.0 on Sept. 13.
6 Sept. Spica, Virgo’s brightest star, lies just a few degrees from a fattening crescent Moon in the southwestern evening sky.
7-8 Sept. Saturn reaches opposition and rises in the east as the Sun sets in the west. Like last year, the planet lies in the constellation Aquarius as it makes its closest approach to Earth in 2024. The planet is slowly moving northwards and now lies about 7º south of the celestial equator so it’s well positioned for all observers to get good views of its magnificent ring system. It’s worth the effort: Saturn is one of the most beautiful objects to observe in a telescope. At opposition, its disk spans about 19” and its rings about 44”. The rings are tilted just 3º to our point of view this year which makes for a unique view. Our Saturn Observing Guide will help you get a good view of this lovely celestial object and understand what to look for. Saturn remains visible through the rest of the year.
9 Sept. Look to the east-northeast for Regulus and Mercury rising together in the morning twilight sky. The pair are separated by about half a degree.
10 Sept. As northern summer winds down, the bright star Antares flickers bright in the southwestern sky as darkness falls. This evening a half-lit Moon hovers about 6 degrees east of the red supergiant.
11 Sept. First Quarter Moon, 06:06 UT
17 Sept. A full Moon lies about 2 degrees south of Saturn in the southern sky. Observers in western North America, Hawaii, and northern Australia will see the Moon occult Saturn in the early morning hours (early evening in Australia). Find timing of the occultation for dozens of locations at this link.
17-18 Sept. A modest partial lunar eclipse is visible in most of the Americas. Greatest eclipse occurs at 02:44 UT on Sept. 18th (that’s 10:44 p.m. EDT, for example). The northern part of the Moon passes through the umbra so a slight darkening will be visible.
18 Sept. Full Moon, 02:34 UT
21 Sept. Neptune reaches opposition near the ‘Circlet of Pisces’, about 5 degrees south-southeast of the star Lambda Piscium. The planet itself, which lies today at a distance of 4.3 billion kilometers, shines at magnitude 7.8 and spans a diameter of just 2.4”. You can spot the planet in binoculars, but you need a telescope at about 150x or more to reveal its pale blue-green disk.
22 Sept. Taurus rises higher in the early-morning sky and today a waning gibbous Moon passes across the Pleiades star cluster.
22 Sept. The Sun crosses the celestial equator moving south at 12:44 UT. This marks the beginning of autumn in the northern hemisphere and spring in the southern hemisphere.
24 Sept. Last Quarter Moon, 18:50 UT, (the ‘Harvest Moon”’).
24 Sept. Comet C/2023 (A3) Tshuchinshan-ATLAS reaches perihelion about 0.39 AU from the Sun. Later in the month, the comet emerges into the morning sky for southern hemisphere observers and in October into the evening sky for northern hemisphere observers. Here’s a guide to help you see this possibly spectacular comet for yourself.
25 Sept. Look eastward well before sunrise to spot Mars rising 5 degrees south of a thick lunar crescent. Wedged between the knees of Gemini, Mars shines at magnitude +0.5 and shows a disk about 7.3” wide. It may tantalize telescopic observers with a few surface details on nights and mornings of rock-solid seeing.