Skywatch Line for Wednesday and Thursday, February 26 and 27, 2025, written by Alan French
This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, February 26 and 27, 2025, written by Alan French.
The Sun rises at 6:35 A.M. on Wednesday and sets at 5:41 P.M. On Thursday it rises at 6:34 A.M. and sets at 5:43 P.M. This Thursday gained 19 minutes; 47 seconds of daylight compared to last Thursday. At the end of the month, we will have gained 1 hour and just over 17 minutes of daylight compared to the last day of January.
The Moon was at last quarter on Thursday, February 20, and is now approaching new. It will be new early Thursday evening. It is out of sight now.
At 7:00 P.M. Venus will be 17 degrees above the western horizon, still at magnitude -4.6. Through a telescope, on Wednesday at 7:00 P.M., Venus appears 47.3 arcseconds across and 16.5% sunlit. By Thursday at 7:00, it will be 48 arcseconds across and 15.5% sunlit. While the difference may not be obvious by eye, especially with views separated in time, it illustrates how fast things are now changing.
At 7:00 P.M. bright Jupiter is high in the south southwest, standing 66 degrees above the horizon and well placed for telescope observations. As we often mention, even a small telescope will reveal the four largest and brightest moons of Jupiter, the Galilean moons, Io, Europa, Ganymede, and Callisto, appearing as stars to either side of the planet and roughly in line. Sometimes, of course, a moon might be passing in front of or behind the planet.
When passing behind the planet, moving west to east, the moon is occulted by Jupiter. Jupiter also casts a shadow, and a moon may be invisible because it where we should see it, but it is in the planet’s shadow and not reflecting sunlight, eclipsed by the planet. With Jupiter past opposition, we see the planet’s shadow to its east. Moons moving out from behind the planet toward the east are eclipsed by the planet’s shadow and do not appear until they have moved some distance from Jupiter’s limb and back into sunlight.
When moving east to west the moons will be passing in front of Jupiter. When the moon is in front of the planet it can be hard to see, visibility depends on the contrast between the moon and the belt or band it is in front of. The moons cast a shadow that is very black, and those are easy to see against the bright cloud tops. As with the planet, since we are past opposition, the moon’s shadows are to their east, and they move onto the planet after the moon itself.
On Wednesday night at 7:00 P.M. all four moons are the west of Jupiter. Io is closed to the planet with Europa next. Callisto and Ganymede are farther out and close together, with Callisto to the north.
At 7:00 P.M. Thursday Io and Europa are to the east of Jupiter, with Europa farthest away, and Ganymede and Callisto to the west, with Callisto a good distance farther away than Ganymede.