This is Dudley Observatory’s Skywatch Line for Friday, July 31, through Sunday, August 2, written by Sam Salem.
On Friday, Sun rises at 5:46am and sets at 8:16pm; Moon sets at 2:30am and rises at 6:19pm. The waxing gibbous Moon shines just over the Sagittarius Teapot on Friday evening. On Saturday evening, the nearly full Moon forms a triangle with Jupiter and Saturn. Shortly before dusk, the Moon, Jupiter, and Saturn will rise together over the southeastern horizon, with the Moon positioned directly below bright Jupiter. The Moon and Jupiter will fit into the field of view of binoculars. As they cross the sky during the night, the Moon will creep east, towards dimmer Saturn, and the diurnal rotation of the sky will move Jupiter below the Moon.
This weekend, view Venus and Mercury preceding the Sun in the eastern sky, an hour before sunrise. At that time, Venus is about 24 degrees high, while Mercury is just about 3 degrees above the horizon. The two will gain altitude with time but the sky will continue to brighten as well. Magnitude –4.6 Venus is receding from Earth. This weekend, it appears 43 percent lit, but its disk is only 27 arcseconds across. Venus is located about between the bright stars Aldebaran in Taurus and Betelgeuse in Orion, just northeast of a line between the two. It’s nearly level with magnitude 3 Alheka, Taurus’ zeta star. When the very bright planet Venus rises in the east at around 3am, it will be positioned less than a finger’s width to the upper left of the Ruby Star. That star, also designated 119 Tauri and CE Tauri, is a giant, aging, pulsating variable star that shines with a deep red color. The pair will be visible in binoculars and backyard telescopes until the sky begins to brighten. At magnitude -4.6, Venus will outshine the magnitude +4.3 star by a factor of nearly 3,500. Mercury, at magnitude –0.7, is 68 percent lit and 6 arcseconds wide. It’s located in Gemini the Twins, whose bright stars Castor and Pollux glow nearby. Pollux is just 7 degrees northeast of Mercury.
Mars, at magnitude –1.0, rises due east around midnight, a bright yellow-orange fire-spark, between constellations Pisces and Cetus. Watch Mars rise below the Great Square of Pegasus. By dawn Mars shines high and bright in the south-southeast. In a telescope, Mars grows to 14 arcseconds in apparent diameter, which is as big as it appears at some oppositions. Around this year’s opposition of Mars in early October, it will appear 22.6 arcseconds wide. Mars is still very gibbous, 86% sunlit. In a telescope, look for its white South Polar cap and for subtler dark surface markings. Uranus, at magnitude 5.8 in constellation Aries, is high in the east before dawn, far to the east of Mars. Neptune, at magnitude 7.8 in constellation Aquarius, is high in the south before dawn, far west of Mars.
Comet C/2020 F3 NEOWISE has passed Earth on its way back out of the Solar System. The comet’s increasing distance from Earth and the continuous reduction in heating from the Sun are causing NEOWISE to fade in brightness over time. It’s a lot harder to see with naked eyes now. It will be visible in binoculars and telescopes for another couple of weeks. Then, it becomes a telescope-only target after about mid-August.