All three bright outer planets remain prominent in the evening sky this July.
At dusk, find bright Jupiter in the west-southwest to west, apricot-colored Mars in the southern sky, and Saturn not far to the left of Mars. Venus passed behind the sun in early June, but by mid-July, it emerges into our early evening sky very low in the west-northwest bright twilight glow, 20 minutes after sunset. Look from a place with a view unobstructed by mountains, and use binoculars to help you spot Venus in bright twilight in its first weeks. Binoculars will reveal Mercury near Venus from mid-July until late August. That’ll bring the total to all five bright planets visible simultaneously!
Attend a star party hosted by one of the local astronomy clubs for telescopic views of Jupiter’s cloud belts and four largest moons; Saturn’s spectacular rings and largest moon Titan; the south polar cap and other markings on Mars; and many deep-sky wonders beyond the solar system, in our Milky Way galaxy, and beyond!
Our chart depicting the sky at evening mid-twilight in July follows positions of naked-eye planets and stars of first magnitude or brighter in the sky when the sun is 9 degrees below the horizon, roughly 45 minutes after sunset. Planets are plotted as dots, one for each day, with labels for dates at weekly intervals.
On this map, you’ll find bright Jupiter starting well up, a little south of due west, at dusk in early July 2016, with faint Regulus, heart of Leo, preceding it as they sink toward the western horizon over the course of the month.
Mars starts a little east of due south at dusk in early July. Note the shape of the triangle it forms with Saturn to its left, and the red twinkling star Antares, heart of the Scorpion, below Saturn. The triangle will shrink in coming weeks.
The Summer Triangle of Vega, Deneband Altair ascends the eastern sky at dusk in July. Its brightest star, blue-white Vega, marks the top of the triangle. Two other bright stars, golden Arcturus and blue-white Spica, are high in the southwest quarter of the sky.
Mercury and Venus first appear on our evening mid-twilight chart in late July, but if you observe earlier in twilight, some 20 to 30 minutes after sunset, and use binoculars, you can catch their closest pairing very low in the west-northwest on July 16, as Mercury (magnitude -1.0) passes just 0.5 degrees north (to the upper right) of Venus (-3.9). (You’ll need a viewing site where mountains don’t block your view!) On the previous evening, July 15, you can spot Mercury 0.8 degrees to the right of Venus, with the two setting at about the same time. On following evenings, Mercury shifts to the upper right of Venus, and next above it, and then toward Venus’ upper left, with their separation widening. During July 16-Aug. 19, Mercury appears higher than Venus, and sets as much as 18 minutes after Venus during from July 30 to Aug. 4.
Follow the moon: Its day-to-day change in position against the stars, averaging 13 degrees per day, is much more noticeable than that of the planets. Watch the moon change from a thin crescent to just past full July 5-20, while passing the planets and the bright stars plotted on our evening twilight charts. Watch for these events:
Tuesday, July 5: See the first crescent moon, age 40.5 hours after new, half an hour after sunset. Binoculars give fine views of this thin moon very low in the west-northwest, provided mountains don’t obstruct your view. Sighting of this crescent marks the start of a new month, ending the fasting month of Ramadan.
Thursday, July 7: Regulus, heart of Leo, appears closely north of the crescent moon.
July 8 and 9: Jupiter is closely to the upper left of the moon on Friday, then not-so-closely to the lower right of the moon on Saturday.
Monday, July 11: The moon is near first quarter phase. Look for the star Spica, the spike of wheat in hand of Virgo, a few degrees north of the moon.
July 13 and 14: Mars is widely to the lower left of the gibbous moon on Wednesday, and not-so-widely to the lower right of the moon on Thursday.
Friday, July 15: Saturn is closely below the moon. Note Antares, heart of Scorpius, the Scorpion, below Saturn.
Saturday, July 16: A close pairing of Mercury-Venus in bright twilight is described above.
Tuesday, July 19: The moon passes full phase shortly before 4 p.m., and rises in the east-southeast at 7:45 p.m., or 10 minutes before sunset in Palm Springs. Because of our surrounding mountains, you must wait several minutes until the moon’s disk begins to appear.
Watch for the moonrise on subsequent evenings: Wednesday, July 20, at 8:30 p.m.; Thursday, July 21, at 9:12 p.m.; Friday, July 22, at 9:52 p.m.; Saturday, July 23, at 10:31 p.m.; Sunday, July 24, at 11:10 p.m., nearly due east; and Monday, July 25, at 11:49 p.m. You’ll notice the moon rising farther north each night until night of July 30-31, when it will rise in the east-northeast at 3:31 a.m. on Sunday morning, July 31.
Early in July, before the moon gets bright, and again beginning around July 22 or 23—when the waning moon after full starts rising late in the evening—go to a dark location after nightfall and enjoy spectacular views of the summer Milky Way. Follow its path from the “W” of Cassiopeia low in the north-northeast, through the Summer Triangle along the Northern Cross, or neck of Cygnus, the Swan, then down toward the Teapot of Sagittarius to the left of Scorpius in the southern sky. Part of the Milky Way resembles a puff of steam rising out of the spout of the Teapot. From within the Summer Triangle and southward, look for the long Great Rift, where the river of the Milky Way is divided into two streams by clouds of obscuring interstellar dust in the foreground blocking the light of the stars beyond. A pair of binoculars will easily resolve the bright Cygnus Star Cloud (where we look into our own spiral arm, along the neck of the Swan) into multitudes of stars!
Telescopic views of planets: Jupiter’s dark equatorial cloud belts and up to four of the bright satellites discovered by Galileo offer a pleasing view for small telescopes.
Mars, still showing a fair-sized disk after its closest approach in late May, displays surface detail! This month, Mars’ southern hemisphere spring equinox will occur on July 4. Although the south pole of Mars is then on the Martian terminator (day-night boundary), that pole is now tipped 15 degrees out of Earth’s view—the surrounding south polar cap of frozen carbon dioxiode (or its overlying cloud cover) is near its maximum extent, reaching halfway from pole to equator, far enough to spill over the southern limb. So whenever you look at Mars early this summer, you’ll see a bright southern edge to Mars’ disk.
Enjoy Saturn’s rings this summer! They’re now tipped from edge-on by almost the greatest angle possible. Using as high of a magnification as your telescope and atmospheric conditions allow (I often use 200x with my 6-inch reflector), try for the Cassini Division dividing the outer A ring from the broader, brighter B ring. This narrow gap is nearly two-thirds of the way from the inner edge of B toward the outer edge of A. Look also for Titan, Saturn’s largest moon, taking 16 days to complete one circuit about the planet. Its nearly circular orbit is almost nine times as large as the outer edge of Saturn’s A ring, in nearly the same plane as the rings now tipped 26 degrees from edge-on, and so it appears as an ellipse.
Titan will appear farthest west of Saturn on July 3 and 19, and farthest east on July 11 and 27. We are seeing the north face of the rings and of Titan’s orbit, so we’ll see Titan at superior conjunction (the far side of Saturn) four days after it appears farthest to the west, and at inferior conjunction (near side of Saturn) passing south of the planet four days after greatest elongation east.
Venus, just emerged from the far side of the sun, appears tiny and full, and low in twilight. It will become much more interesting for telescopic viewing as it nears the end of its evening apparition.
Predawn sky: There are no morning planets visible to the unaided eye in July. (Uranus and Neptune require at least binoculars and detailed finder charts.) But cooler mornings make for more comfortable sky viewing. As dawn begins to brighten, we find the Summer Triangle well up in the western sky, getting lower as the month progresses. Fomalhaut, mouth of the Southern Fish, is in south to south-southwest, and Capella, the Mother Goat star, is ascending in the northeast. To Capella’s lower right, we find ruddy Aldebaran, eye of Taurus the Bull. Before the sky brightens, look above Aldebaran for the beautiful Pleiades star cluster (the Seven Sisters), a wonderful target for binoculars!
Late in July, the two brightest stars of Orion the Hunter rise into view: reddish Betelgeuse with blue-white Rigel to its right. Between them lies the Hunter’s belt of three stars in a nearly vertical line. Orion will rise two hours earlier as each month passes.
The Astronomical Society of the Desert hosts monthly star parties at Sawmill Trailhead (elevation 4,000 feet). For dates, with map and directions to the site, visit the Society’s website at www.astrorx.org.
Sky’s the Limit Observatory in Twentynine Palms offers star parties most Saturday evenings, except when the moon is close to full. For details, visit www.skysthelimit29.org.
Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. Robert D. Miller, who provided the twilight charts, did graduate work in planetarium science and later astronomy and computer science at Michigan State University. He remains active in research and public outreach in astronomy. Dr. Jeffrey L. Hunt, a retired planetarium director now living in the Chicago area, did the Venus map below. He has taught astronomy and sky watching to all ages. He studied astronomy education at Abrams Planetarium at Michigan State University. Jeff writes an astronomy blog at jeffreylhunt.wordpress.com and can be followed on Twitter at @jeff_hunt.