Poster’s Note: The text for this month’s installment from Dee Sharples, “The Sky In September 2025,” is provided below. Those wishing to listen to the article can click on the audio link below.
In September, the number of hours of darkness are increasing and we should still experience plenty of mild temperatures for observing the night sky. The autumn equinox occurs on Monday, September 22nd, at 2:19 p.m. EDT. The hours of daylight and darkness will be almost equal with 12h 9m 4s of daylight, almost half the hours in a day. But on Thursday, September 25th, the number of hours of daylight and darkness will be even more equal with sunrise at 7:01 a.m. and sunset at 7:01 p.m., with 12h 0m 9s of daylight.
The planet Saturn can be found in the eastern sky in the evening, high in the southern sky at midnight, and setting in the west in the early morning. It will shine at magnitude 0.6 looking like a medium-bright yellowish star.
At the beginning of September, Neptune, the most distant planet in our solar system, will be visible in binoculars just 1.7° northeast of Saturn ending the month 3° away. This separation increases because of the faster speed Saturn travels around the Sun. Neptune will shine with a bluish hue at a dim magnitude 7.7. It’s 2.8 billion miles from the Sun, taking 165 Earth years to orbit the Sun once, so its movement among the stars can hardly be noticed.
Saturn is only 886 million miles from the Sun and takes 29.5 Earth years to orbit it once. For comparison, our Earth lies 93 million miles from the Sun and takes 365.25 days (that’s 1 year) to orbit once. Center Saturn in your binoculars and move them half of your field of view, and Neptune will be near the center of your eyepiece.
Jupiter will rise in the east by 3:00 a.m. on September 1st and a few hours earlier by the end of September. It will be very bright at magnitude –2.0, and viewing it through even a small telescope will show the dynamic orbits of the four Galilean moons (Io, Europa, Ganymede, and Callisto) around Jupiter.
This montage shows the best views of Jupiter’s four large Galilean moons as seen by the New Horizons spacecraft during its flyby of Jupiter in late February 2007. The four moons are, from left to right: Io, Europa, Ganymede and Callisto. The images have been scaled to represent the true relative sizes of the four moons and are arranged in their order from Jupiter. Io, 2,260 miles in diameter; Europa, 1,938 miles in diameter; Ganymede, 3,268 miles in diameter; Callisto, 2,995 miles in diameter.
Venus, at a brilliant magnitude -3.9, rises in the east at 4:00 a.m. on September 1st. The pretty Beehive star cluster (M44) will be just 1° north of the planet, and both will be 20° above the horizon at 6:00 a.m.
A quick way to measure distances in the night sky is to hold your hand out at arm’s length. Using your fingers and fist as a ruler, the amount of sky blocked by your little finger is equal to 1°, the amount blocked by three fingers is 5°, the amount blocked by your fist is 10°. Move them between the horizon and an object, or between objects, to estimate how far apart they are.
