This is Dudley Observatory’s Skywatch Line for Friday, June 26, through Sunday, June 28, written by Sam Salem.
On Friday, Sun rises at 5:19am and sets at 8:38pm; Moon sets at 12:08am and rises at 10:56am.
On Saturday evening, the Moon shines about 8 degrees under Leo’s 2nd-magnitude tail-tip star, Denebola. Denebola forms an almost perfectly equilateral triangle with brighter Spica off to its left and Arcturus above them. All three sides of the triangle are close to 35 degrees long. This has been called the Spring Triangle. The Moon reaches its first quarter phase on Sunday, at 4:16 a.m. At that time, the relative positions of the Earth, Sun, and Moon will cause us to see the Moon half-illuminated on its right-hand side. Sunlight striking the Moon at a shallow angle produces spectacularly illuminated landscapes along the pole-to-pole terminator line that separates the lit and dark hemispheres. First quarter moons always rise around noon and set at midnight, so they are visible starting in the afternoon hours.
Several times a year, for a few hours near its first quarter phase, a feature on the Moon called the Lunar X becomes visible in strong binoculars and backyard telescopes. If skies are clear, point your lenses to the Moon this Saturday around 8pm. The Lunar X is predicted to peak in intensity at 8pm, but the phenomenon will be visible for approximately two hours on either side of that time. When the rims of the craters Parbach, la Caille, and Blanchinus are illuminated from a particular angle of sunlight, they form a small, but very obvious X-shape. The Lunar X is located near the terminator, about one third of the way up from the southern pole of the Moon. The prominent round crater Werner sits to its lower right.
Venus is getting a little higher and easier to spot every morning in the east-northeast as dawn brightens. Venus is low in the dawn, look for it just above the east-northeast horizon. If you look early enough before dawn grows bright you may be able to catch the Pleiades 9 degrees above it. Venus is on its way up to a fine showing as the bright Morning Star through summer and fall. Mars, at magnitude –0.4, rises in the east around 1am shining bright orange at the Aquarius-Pisces border. Watch for it to clear the horizon lower right of the Great Square of Pegasus. By the first light of dawn, Mars shines high and prominent in the southeast. In a telescope Mars has grown to 11 arc-seconds in apparent diameter. Mars is as gibbous as it gets, 84% sunlit. Mars will appear fully twice this diameter when it passes closest by Earth around opposition in the first half of October. Neptune, at magnitude 7.9 in constellation Aquarius, is well up in the southeast before dawn begins, in the vicinity of Mars.
Jupiter and Saturn now rise around the end of twilight. Jupiter rises first, then dimmer Saturn follows, about 20 minutes behind, lower left of Jupiter. The planets are about 5½ degrees apart. Look farther to Jupiter’s right to see the Sagittarius Teapot resting upright. The two giant planets shine at their highest and telescopic best around 3 a.m. Jupiter and Saturn straddle the border of constellations Sagittarius and Capricornus. Jupiter will reach opposition on the night of July 13th, Saturn on July 20th.