Astronomical autumn begins on September 22nd at 9:54 p.m. Eastern Daylight Time or 1:54 UTC on September 23rd. The sun shines directly overhead at the equator, and day and night are roughly equal at about 12 hours each for all areas around the planet and everyone sees the sun rise due east and set due west. The equinox, and for a few weeks before and after, are often also known for challenging morning and evening commutes with east-west roads aligning with the sun, making glare and driving in general challenging.
Besides the equinox, here are a few other astronomical highlights for the month of September. First, lets look at our nearest neighbor, the moon:
Sept 3: Last quarter
Sept 9: New moon
Sept 16-17: First quarter
Sept 25: Full moon (Harvest moon)
So, the first half of September will provide the best opportunity for evening stargazing before bright moon light washes out deep sky objects during the evening hours after mid-month.
The four brightest planets are also still visible in the evening sky during September, with Venus and Jupiter setting in the west early in the evening, while Saturn and Mars remain fairly high in the Southwest and South during the evening hours respectively. While Venus is growing larger in apparent size, all the other three planets are growing smaller in apparent size each day, so try to view them early in the month when they are as high in the sky as possible, which means right after sunset.
On September 25th Venus reaches its maximum brightness, at magnitude -4.6, the same day as the full moon.
In terms of deep sky objects, the ring (M57) and dumbbell (M27) nebulas are high overhead during the evening hours and situated for good viewing. The great globular cluster in Hercules M13, is still high in the west during the evening and is a great sight in telescopes 8" and larger in aperture, still nice in 6" scopes, and visible, though not well resolved into individual stars, in smaller scopes. The Andromeda galaxy (M31) is rising higher in the sky in the east during the evening each day, and is also a nice evening sky target now as well. The multitude of wonderful deep sky objects in Sagittarius are starting to shift lower into the southwestern portion of the sky during the evening hours during September. So, this will be the last chance to view many of them before they start to set to close to nightfall later this fall.
In order to locate many of these objects I highly recommend Sky Safari (https://skysafariastronomy.com) for mobile phones and tablets, Stellarium (https://stellarium.org/) for your computer, or if you want to go old school and take printed paper outside with you, Skymaps.com is hard to beat. Here is the PDF you can print for the month of September from the www.skymaps.com website: http://www.skymaps.com/skymaps/tesmn1809.pdf
Be sure to take advantage of the cooler, drier evenings that fall brings to take a peak at the night sky.