What to See in the Night Sky in September 2023

From fall’s official welcome to a trio of brightly visible planets, this month is all about change.

Michael d'Estries

Published August 31, 2023

Dust off that sweatshirt, grab a blanket, and enjoy the waning weeks of summer while you're looking up into the evening sky. Below are just some of the beautiful celestial highlights to look forward to in September 2023.

September’s Late New Moon Gives Way to Dark Skies (Sept. 14)

September’s new moon will arrive on Sept. 14, with the lunar surface illuminated by the sun facing away from Earth. This phenomenon will give way to exceptionally dark skies devoid of moonlight and perfect for observing galaxies, planets, and other celestial wonders.

If you want a dark sky target, try finding the Andromeda Galaxy. Located approximately 2.5 million light-years from Earth, it’s the farthest object visible to the naked eye. To locate it, head out when skies are completely dark and look to the lower-right of the constellation Cassiopeia (a series of stars shaped like an "M" or "W"). Andromeda will appear as a glowing smudge on the sky. If you own a pair of binoculars, bring those along to help enhance the view!

If you happen to be immortal, you can expect views of the Andromeda Galaxy to improve over time. Astronomers estimate that in 4 to 5 billion years, our own Milky Way Galaxy and Andromeda will collide and combine to form one giant elliptical galaxy. You can view a simulation of how spectacular our night sky will become as a result of this collision here.

Venus Puts on a Spectacular Morning Show (Sept. 18)

For those of you who rise early, Venus has been practically impossible to miss over the last several weeks. The second planet from the Sun has been steadily increasing in brightness, and this crescendo will culminate on Sept. 18th, when Venus achieves its peak luminosity for this cycle. On this day, the "morning star," as it's often referred to, will be at its most radiant, outshining other heavenly bodies in the pre-dawn sky.

But this dazzling display won't last indefinitely. After reaching this zenith of brightness, Venus will begin its gradual transition back towards the sun's vicinity. Over time, it will shift from its position as a beacon in the morning to a brilliant point of light in the evening skies. So, if you haven't already, make sure to take a moment in the early morning to appreciate this natural wonder. It's a celestial treat that's hard to ignore!

Neptune at its Closest (and Brightest) to Earth (Sept. 19)

Neptune, the eighth and farthest known planet in our solar system (sorry, Pluto!), will reach its annual opposition (when the Earth passes between it and the Sun) on Sept. 19th. Despite having a mass 17 times that of Earth, this gas giant is so far away (it takes light four hours to travel between Neptune and Earth during opposition) that it appears very dim even at its closest. To view it, Earth-Sky recommends consulting this chart from TheSkyLive and investing in a tripod-mounted pair of binoculars or a telescope.

Fun fact: Neptune’s winds can reach speeds up to 1,500 mph—the fastest yet detected in our solar system. It’s also our coldest planet, dipping down to temperatures of -366.6 F. Have your stargazing guests ponder that while you attempt to locate this blue-tinged wonder.

Bid Adieu to Summer and Greet the Fall Equinox (Sept. 23)

The first day of autumn in the Northern Hemisphere will officially arrive on this day, and for our friends in the Southern Hemisphere, it's the first day of spring! At 2:49 a.m. EDT, we'll say goodbye to the balmy days of summer and welcome the start of fall with the autumnal equinox. The autumnal equinox happens the moment the sun crosses the celestial equator, which is an imaginary line in the sky that corresponds to Earth’s equator.

In anticipation of the colder months ahead, the fall equinox offers an important reminder to start thinking about firewood, pumpkins, and dusting off your warmer clothing. According to the Farmers' Almanac’s long-range forecast (which, like any long-range weather forecast, should be taken with a grain of salt), the coming winter will make “cold-weather fans rejoice,” with "more snow and low temperatures nationwide.”

View Tiny Mercury at its Brightest (Sept. 22)

Mercury, the smallest of our solar system’s planets, will make itself a bit easier to spot in the early morning of September 22 as it reaches its greatest elongation. Leading up to this date, Mercury will brighten from magnitude -0.3 to -1.0. The only downside to all of this is that Mercury will only reach 15 degrees above the horizon before dawn spoils the show, so make sure you have a clear view of the eastern horizon.

Catch a View of the Harvest Moon (Sept. 28)

September’s full moon, nicknamed the "harvest moon," will rise on the evening of Sept. 28th and reach peak illumination at 5:58 a.m. EDT on the morning of the 29th.

As its name implies, this full moon is so-called due to its timing (rising for several days just after sunset) in providing crucial light to farmers harvesting their crops. Unlike other full moons, the naming of this one is tied specifically to the fall equinox. As such, the harvest moon can sometimes occur in early October (as it did in 2020). When that happens, September’s full moon is appropriately called the “corn moon.”

Welcome Back the Haunting Zodiacal Light (late September)

This celestial object (aka the Zodiacal light) also signals the start of fall for the Northern Hemisphere. It's described as a "cone-shaped glow," similar to the Milky Way's dusty look, but made out of comet and asteroid dust. It’s estimated that for this phenomenon to remain a steady presence in our skies, some three billion tons of matter must be injected into it each year by comets. For best viewing, look up your local sunrise time and subtract an hour—and make plenty of coffee to keep you awake as this "false dawn" appears.

https://www.treehugger.com/what-to-see-night-sky-september-2023

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