Skywatch Line for Monday and Tuesday, September 22 and 23, 2025, written by Alan French
This is Dudley Observatory’s Skywatch Line for Monday and Tuesday, September 22 and 23, 2025, written by Alan French.
The Sun rises at 6:43 A.M. on Monday and sets at 6:52 P.M. On Tuesday it rises at 6:44 A.M. and sets at 6:50 P.M.
Happy Autumnal Equinox! The Autumanl Equinox marks the time when the Sun, in its journey southward, is above the equator and we enjoy approximately equally long days and nights. This year it occurs at 2:19 P.M on Monday, the 22nd. It marks the beginning of fall. The Sun will continue to move south and lower in our skies until the beginning of winter, the Winter Solstice.
In the Southern Hemisphere this is the Vernal Equinox and the beginning of spring. While our days continue to grow shorter, in the southern hemisphere days will continue to lengthen as the Sun moves higher in their sky.
The Moon was new on Sunday afternoon and is moving toward first quarter. The ecliptic now makes a shallow angle with the horizon and is very low across the sky. The Moon is also south of the ecliptic, so these young Moons are not much higher than the Sun, set soon after sunset, and are deep in bright evening twilight. Monday’s slender 1.6% crescent sets only 12 minutes after sunset. Tuesday’s 4.3% sunlit Moon sets 33 minutes after sunset, but at 7:10 P.M. will be not quite 2 degrees above the horizon. If you have a good view 20 degrees south of the sunset location (west) and clear skies near the horizon, there is a chance to catch Tuesday’s Moon.
As the Moon moves toward first quarter it will remain low in the sky after sunset. When it reaches first quarter next Monday it will only be 16 ½ degrees high at 8:00 P.M.
Saturn, which reached opposition early Sunday, is 31 degrees above the southeastern horizon at 10:00 P.M. It shines at magnitude +0.6 now, a modest gain of 0.1 magnitude in the last month. In the coming month it will only lose 0.2 magnitudes. The planet’s lovely rings are now tilted only 2 degrees from our vantage point. Although not at their most impressive, they are visible through telescopes. We will again enjoy them with their maximum tilt, and most impressive views, in 2032.
Jupiter still rises after midnight but is rising earlier each night. On Tuesday morning it rises at 12:49 A.M. and is due south and highest at 8:08 A.M. The best time to catch Jupiter is around 5:30 A.M., when the sky is still dark and it is toward the southeast and 49 degrees high. Jupiter’s four brightest moons appear as stars, roughly in line, to either side of the planet in any telescope and can even be spotted in steadily held binoculars when well away from the planet.
At 5:30 Tuesday morning Europa and Io will be to the east of the planet, close together, and Callisto and Ganymede will be to the west, with Ganymede almost three times as far from Jupiter as Callisto. At 5:30 A.M. Wednesday, Callisto will be to the east and Io, Europa, and Ganymede will be to the west, with Io closest to Jupiter and Ganymede farthest away.