This is Dudley Observatory’s Skywatch Line for Friday, July 3, through Sunday, July 5, written by Sam Salem.
On Friday, Sun rises at 5:22am and sets at 8:37pm; Moon sets at 3:48am and rises at 7:27pm.
The Moon will reach its full phase on Sunday, at 12:44 a.m. This full Moon will feature a shallow penumbral lunar eclipse. The entire eclipse will be visible from all of Central and South America, the southeastern half of North America, and western Africa. The latter stages of the eclipse will be visible in the rest of the USA, except Alaska. For us in the Americas, the Moon will turn precisely full during the nighttime hours on Saturday-Sunday, to present a partial Penumbral eclipse of the Moon. It’ll be such a faint eclipse that some will not notice it even while staring straight at it.
On Saturday, at 7:34 a.m. Earth will reach aphelion, its maximum distance from the Sun for this year. The aphelion distance of 94,511,180 miles is 1.67 per cent farther from the Sun, than the mean Earth-Sun separation of 92,955,807.3 miles, which is also defined to be 1 Astronomical Unit (1 AU). Earth’s perihelion, or minimum distance from the Sun, will occur on January 4.
When the full Moon rises over the southeastern horizon at dusk on Sunday, it will form a triangle below Jupiter and dimmer, yellow-tinted Saturn. The Moon and planets will fit within the field of view of binoculars. Over the course of the night, the diurnal rotation of the sky will shift the Moon to the planets’ left, and the Moon’s orbital motion will carry it closer to Saturn than Jupiter. Jupiter and Saturn are now at their best. Later this month, Earth will pass between each of these planets and the Sun, so that both Jupiter and Saturn reach their oppositions. Jupiter reaches opposition on July 13-14 and Saturn on July 20.
In the eastern pre-dawn sky between July 3 and 12, Venus’ orbital motion will carry it directly through the Hyades star cluster, the large, triangular grouping of stars that forms the face of Taurus, the bull. Its traverse offers an opportunity to easily see the daily motion of a planet. Look with unaided eyes while the sky is still somewhat dark, around 4:30 a.m. Use binoculars to nicely frame the planet and the cluster’s stars surrounding it.
From time to time, the small, round, black shadows cast by Jupiter’s four Galilean moons and the Great Red Spot can be seen in amateur telescopes as they cross, or transit, the planet’s disk for a few hours. Starting in late evening on Thursday, and continuing into Friday, see Ganymede’s relatively large shadow traverse the planet, accompanied by the Great Red Spot. Ganymede’s shadow will cross Jupiter’s northern hemisphere between 10:30pm and 1:50am. The spot will complete its passage by 1:30am. With a large telescope look for Ganymede’s pale disk following behind its shadow.