There may be no better month to get outside and look at the stars than September, when warm evenings meet rapidly lengthening nights, the Milky Way remains visible overhead, and the changing seasons can increase your chances of seeing the northern lights.
For stargazers in the Northern Hemisphere, summer presents an obvious problem: Darkness arrives late. By September, however, sunset is getting noticeably earlier each evening, providing far more time under dark skies with mild weather in most locations. Days can still feel summery, while nights tend to remain pleasant enough to spend hours outside with a pair of stargazing binoculars or a good backyard telescope. The only challenge is finding a clear sky.
The balance between daylight and darkness changes particularly quickly around the fall equinox, which occurs on Sept. 22 this year. That's when the sun crosses Earth's equator, bringing day and night close to equal in length around the world. From then on, nights become longer than days across the Northern Hemisphere until the winter solstice on Dec. 21.
As an occasional bonus, auroras tend to occur more frequently around the equinoxes. During this time, the orientation of Earth's magnetic field creates favorable conditions for interactions with the solar wind (the cause of auroras), but there are never any guarantees.
September stargazing highlights
This month, there's plenty happening overhead.
All five planets visible to the naked eye can be seen during September, although not simultaneously; Venus and Mercury are visible in the evening, while Mars and Jupiter come out in the morning. Saturn is visible for much of the night, while Neptune reaches opposition on Sept. 26, meaning it is on the opposite side of Earth as the sun, offering the closest and most direct viewing opportunity.
The moon also passes close to several bright planets during the month (it passed Jupiter before dawn on Sept. 8 and will nudge Venus after dark on Sept. 13 and 14), while the full Harvest Moon rises on Sept. 26, with Saturn following after it minutes later.
September is also one of the last good opportunities of the year for Northern Hemisphere observers to see the brightest parts of the Milky Way in the evening. The star-rich regions of Sagittarius and Scorpius are sinking toward the western horizon, while the iconic Great Square of Pegasus rises in the East to announce the arrival of the autumn sky.
With all those cosmic treats on tap, this month certainly hits the sweet spot for stargazers.
