This is Dudley Observatory’s Skywatch Line for Friday, October 16, through Sunday, October 18, written by Sam Salem.
On Friday, Sun rises at 7:10am and sets at 6:10pm; Moon rises at 6:40am and sets at 6:30pm. New Moon occurs on Friday at 3:31pm. New Moon travels between Earth and the Sun. New Moons travel across the sky with the Sun all day, lost in the sun’s glare. This new Moon occurs only 4.5 hours after perigee, the Moon’s closest approach to Earth, triggering large tides. On Saturday, you might be able to spot the young Moon at day’s end. The Moon will be low in the west, in the glow of sunset. This young, pale, crescent after sunset will be a challenge to spot, even with binoculars. Be sure to find an unobstructed horizon in the direction of sunset.
From time to time, Jupiter’s Great Red Spot (GRS) and the little round, black shadows cast by Jupiter’s four Galilean moons are visible in backyard telescopes as they cross, or transit, the planet’s disk. On Friday, Jupiter’s Great Red Spot should transit Jupiter’s central meridian around 9:22pm. An hour later, at 10:23pm, Jupiter’s moon Io reappears from eclipse out of Jupiter’s shadow just east of the planet, very close to Callisto, with Europa and Ganymede farther out. A small telescope will show Io swelling into view over the course of a couple minutes, turning Callisto into an imitation double star. On Saturday evening, witness the rare event of two shadows transiting with the Great Red Spot. As the sky darkens, the diffuse shadow of Callisto, the crisp, round shadow of closer-in Io, and the great Red Spot will all be completing a group transit event that began before sunset, at 5:25pm. The three objects will rotate off of Jupiter’s limb at 7:25pm.
Mars, at magnitude –2.6 in constellation Pisces, came to opposition last Tuesday. It is still essentially at its closest to Earth, remaining 22.5 to 22.0 arcseconds in apparent diameter. This is bigger that we will see it again until September 2035. Mars is climbing into good view a little earlier every night. In late dusk it glares fiery orange, low in the east. It’s high in the southeast around 11pm, and it’s its highest at its telescopic best around 1am, blazing in the south.
Try to spot Uranus unaided this weekend. Uranus, at magnitude 5.7 in constellation Aries, is well up in the east by 10pm, about 18 degrees east of Mars. Uranus is only 3.7 arcseconds wide, but that’s enough to appear as a tiny fuzzy ball, not a point, at high power in even a small telescope. Neptune, at magnitude 7.8, in constellation Aquarius, is higher in the south-southeast at that time. Neptune is 2.4 arcseconds wide, harder to resolve except in good seeing.
The W-shaped Cassiopeia stands high in the northeast these evenings, a flattened W standing on end. The third segment of the W, counting down from the top, points almost straight down. Extend that segment twice as far down as its own length, and you’re at the Double Cluster in Perseus. This pair of star-swarms is dimly apparent to the unaided eye in a dark sky. Use averted vision to view the Double Cluster by looking directly at the object, but looking a little off to the side, while continuing to concentrate on the object. The Double Cluster is visible with binoculars and it looks lovely in a telescope.