This is Dudley Observatory’s Skywatch Line for Wednesday, May 31, and Thursday, June 1, written by Alan French.
The Sun rises at 5:20 A.M. on Wednesday and sets at 8:26 P.M. On Thursday it rises at 5:20 and sets at 8:27. This Thursday has just over 10 minutes more daylight than last Thursday.
The Moon reached first quarter Saturday and is now moving toward full. On Wednesday the Moon will be toward the southeast as the Sun sets, appearing 88% sunlit. The gibbous Moon will be due south and highest, 35 degrees above the horizon, at 10:16 P.M. Thursday night’s Moon will be lower in the southeast as the Sun sets, and will be due south or transit at 11:04 P.M., appearing 95% full and 28 degrees high. The Moon will reach full late this coming Saturday.
While the full Moon tends to draw photographers, the waxing gibbous Moon offers some enticements. Craters and mountains along the terminator show up well and add interest to a photo, and modern “super-zoon” digital cameras, or a telephoto or an interchangeable lens digital camera provide enough image scale to show these details. Today’s digital cameras allow plenty of room for experimenting with exposure settings, and image processing software allows adjustments for best appearance. This writer generally mounts his camera on a tripod, uses a time delay on the shutter, and underexposes by one stop, slightly adjusting lighting in Photoshop Elements. See what gives you the best results!
Venus continues to dominate the western sky after sunset, now shining at magnitude -4.3. Through a telescope, Venus now appears just over half in sunlight. At it catches up with Earth on its faster, inner orbit, it will grow larger, but we’ll see less of its sunlit face. Brightness increases as it moves closer, but decreases because we see a smaller part of the sunlit face. The two almost balance out, but the increase has a slight upper hand. At its brightest, Venus will reach magnitude -4.7 in early July.
At 9:46, the end of nautical twilight, Venus will be 20 degrees above the western horizon, nicely strutting its brilliance. Nautical twilight is the second phase of twilight, when the horizon is still visible at sea. It ends when the Sun is 12 degrees below the horizon and the horizon is no longer visible. (In the morning, it begins when the Sun is 12 degrees below the horizon.)
The third and darkest phase of twilight is astronomical twilight. The Sun is more than 12 degrees below the horizon, but our atmosphere still scatters some of its light into our night sky and brightens it slightly. With a gibbous Moon in the sky, its effect will be invisible. Astronomical twilight ends when the Sun reaches 18 degrees below the horizon and no sunlight reaches our night sky. For us, that is now 10:39 P.M. The time is mostly of interest to serious stargazers on Moonless nights and under dark skies away from light pollution. New York’s Adirondacks include some of the remaining truly dark skies in the country.
The first phase of twilight, civil twilight, is from when the Sun sets to when its geometric center is six degrees below the horizon. During civil twilight only the brightest stars and planets are visible.