This is Dudley Observatory’s Skywatch Line for Friday, July 12 through Sunday, July 14, written by Sam Salem.
On Friday, Sun rises at 5:28am and sets at 8:34pm; the waxing gibbous Moon rises at 4:48pm and sets at 2:14am. On the evenings of this weekend, watch for the bright waxing gibbous Moon swing by planet Jupiter. On Friday evening, the gibbous Moon forms a triangle with Jupiter, to its lower left, and Antares, the brightest star in constellation Scorpius the scorpion, under it. On Saturday early evening, the waxing gibbous Moon is parked roughly 3 degrees to the left of Jupiter. The conjunction will be a delight in binoculars. Jupiter is so bright that it can easily withstand the lunar glare.
Spotting Mars, at 1.8-magnitude, now requires some effort. It can still be done, but you’re going to need an unobstructed west-northwest horizon and binoculars to catch the planet. We won’t see Mars again for several months. It’s in conjunction with the Sun in September and begins to emerge at dawn in early October. Jupiter gleams at magnitude –2.5. It rises before sunset and is visible in the south-southeast half an hour after sunset. The best time to view Jupiter in a telescope is when it culminates, at roughly 10:30pm. On Saturday evening, all four Galilean moons appear on Jupiter’s celestial west side, relatively close to the planet. Trailing behind Jupiter is 0.1-magnitude Saturn. Venus, at magnitude –3.9, is the sole dawn planet. Like Mars, Venus is nearing the end of its current apparition. The “morning star” pops up in brightening twilight, 45 minutes ahead of the Sun.
Saturn reached opposition on Tuesday. Now is the time to see the ringed planet at its absolute best for the year. The planet is up all night and reaches the meridian around 12:30am. This week it is highest in the south for best telescopic viewing from about midnight to 2am. During this opposition Saturn resides in eastern Sagittarius. Unfortunately, the planet is low in the south even as it crosses the meridian. The situation will slowly improve in the next weeks. In the absence of steady seeing conditions, you’ll often be restricted to low or medium magnification. Even so, Saturn’s magnificent rings will be apparent. The ring system, measured tip to tip, currently appears about as wide as Jupiter’s disk. The rings are tilted toward Earth by an angle of 26 degrees, which is only one degree shy of maximum. This will permit easier sightings of Cassini’s Division, a 4,700-kilometre-wide gap that separates Saturn’s two brightest rings. During moments of steady seeing, the threadlike feature should be visible even in a 60mm refractor. Keep an eye out for Saturn satellites, the brightest of which is 8.5-magnitude Titan, located a few arc-minutes west of the rings this weekend.
After nightfall, Altair, the lowest star of the Summer Triangle, shines in the east-southeast. Altair is the brightest star in constellation Aquila, the eagle. It’s the second-brightest star on the eastern side of the sky, after star Vega climbs high to its upper left. The star name Altair has been used since medieval times. It is an abbreviation of the Arabic phrase “an-nasr aṭ-ṭāʼir “the flying eagle”. Above Altair by a finger-width at arm’s length is little 3rd-magnitude orange Tarazed (Gamma Aquilae). A bit more than a fist-width to Altair’s lower left is compact little constellation Delphinus, the Dolphin, leaping leftward. Look for even smaller, dimmer constellation Sagitta, the Arrow, above the midpoint between Delphinus and Altair.