August 2016 has a rare gift for skywatchers: For most of the month, all five naked-eye planets can be seen during evening twilight, and they participate in beautiful pairings and groupings!
From a site with an unobstructed view of the western horizon, begin within a half-hour after sunset to catch Venus before it sinks too low. Use our evening twilight chart link to guide you. Venus, at magnitude -3.8, is visible with the unaided eye, even low in bright twilight, if you know where to look. (It will get higher in coming months, setting in a dark sky starting in October.)
Jupiter, next in brightness at magnitude -1.7, is easy to find not long after you spot Venus. For most of August, Jupiter appears to the upper left of Venus, getting one degree closer each day until their spectacular close pairing on Saturday, Aug. 27. Thereafter, Jupiter will appear to the lower right of Venus, getting increasingly difficult to see.
Use binoculars all month, if necessary, to catch Mercury, starting August at mag -0.1 while 8 degrees to the upper left of Venus, and fading to magnitude +0.5 by Aug. 24 while 6 degrees to the lower left of Venus.
As the sky darkens, Mars (magnitude -0.8 to -0.3), Saturn (+0.3 to +0.5), and first-magnitude Antares—6 degrees from Saturn all month—become easy for the unaided eye to see. The two planets and the red supergiant star will have a striking arrangement Aug. 23 and 24.
In morning twilight Aug. 4-14, look daily within an hour before sunrise and watch for the first appearance of Procyon, about 6-7 degrees north of east, and Sirius, in the east-southeast. The “Dog Star” Sirius is nearly in line with Orion’s belt, and completes the almost equilateral Winter Trianglewith Betelgeuse (Orion’s shoulder) and Procyon. The name Procyon means “before the dog,” because the star rises several minutes before Sirius does, and so gives notice of the imminent rising of the Dog Star. The heliacal rising (first morning appearance) of Sirius was a very important event in ancient Egypt, as it gave notice of the imminent flooding of the Nile River, which occurred around the summer solstice. Now, because of precession, the 26,000-year wobble of the Earth’s axis, the first appearance of Sirius occurs several weeks after the start of summer and the rise of the Nile.
Aug. 4, beginning 30 minutes after sunset: Find the 2.3-day-old crescent moon low in the west, and Venus 11 degrees to its lower right. Mercury appears 2 degrees to the left of the moon, nearly 9 degrees to the upper left of Venus, and 15 degrees to the lower right of Jupiter. Mars and Saturn are 10 degrees apart in the southern sky. Six solar system bodies—Venus-Mercury-moon-Jupiter-Mars-Saturn—span 100 degrees.
Aug. 5: Jupiter is about 1 degree above the moon.
Aug. 6: Three planets, Jupiter-Mercury-Venus, appear 12 degrees, 24 degrees and 33 degrees to the lower right of the moon. Mars and Saturn appear 57 degrees and 65 degrees to the moon’s upper left. Venus and Mars appear 90 degrees apart—in quadrature—this evening. Verify that by observation!
Aug. 7 and 8: The moon is near Spica, brightest star in Virgo.
Aug. 8 and 9: Mars is 0.9 degrees from Delta Scorpii, the middle and brightest of three stars in the head of the Scorpion.
Aug. 10: The moon passes first quarter phase at 11:21 a.m. Tip for telescopic observation of the moon in daytime:When the moon is within two days before or after half full—this month, on the afternoons of Aug. 8-11, near first quarter phase, and on mornings of Aug. 23-26, near last quarter phase—thread a singlepolarizing filter into a low-power eyepiece of your telescope. Next, while viewing the moon, rotate the eyepiece until the blue sky surrounding the moon appears darkest, increasing contrast of the moon against the sky for wonderful daytime views of lunar craters and other features!
Aug. 11-12: As darkness falls, note the beautiful diamond-shaped arrangement of moon-Mars-Antares-Saturn, about 6-7 degrees on each side. The peak of the Perseid meteor shower occurs after moonset, in Friday, Aug. 12’s predawn darkness hours! The dark, moonless sky should be wonderful for observing meteors.
Aug. 12: The moon is 8 degrees to the upper left of Saturn. The famous ringed planet marks the top vertex of an attractive triangle of three “stars.” Compare the color and brightness of its two other members, Mars and Antares. Venus is 15 degrees to the lower right of Jupiter, getting a degree closer each day!
Aug. 16: Mercury is at its greatest elongation, 27 degrees east of the sun. Since Mercury is more to the left of the setting sun, rather than high above it, the planet sets well before darkness falls; this is an unfavorable apparition for observers at mid-northern latitudes, despite Mercury’s unusually large angular distance from the sun. Here in Southern California, we will have an easier time spotting it than folks in northern part of the state.
Aug. 17-18: Venus is 10 degrees to the lower right of Jupiter at dusk. Five planets span 84 degrees. Also, the full moon occurs overnight, at 2:26 a.m. on the 18th. The moon shines with enhanced brightness in that hour as it narrowly misses the penumbra of Earth’s shadow and reflects sunlight toward us.
Aug. 19: Mercury is 3.8 degrees to the lower left of Jupiter, their minimum distance apart in a quasi-conjunction.
Aug. 22: Venus is 4.9 degrees to the lower right of Jupiter.
Aug. 23: Venus and Jupiter are within 3.9 degrees; Mercury and Jupiter 4.3 degrees; and Mercury and Venus 6.4 degrees, in a nearly isosceles triangle.
Aug. 23 and 24: In order from top to bottom, Saturn, Mars and Antares nearly line up, as Mars goes 4.4 degrees south of Saturn and 1.8 degrees north of Antares!
Aug. 25, predawn (using a telescope): The moon occults 3.7-magnitude Gamma Tauri, point of “V” of Hyades star cluster, from 1:17-2:10 a.m. in the Coachella Valley. The daytime occultation of Aldebaran is visible through a telescope: Disappearance on the moon’s bright side occurs in here at 10:24 a.m., with reappearance at the moon’s dark side at 11:27 a.m. Last quarter phase occurred on Aug. 24, at 8:41 p.m., so the moon on Aug. 25 is a fat crescent. Follow waning moon mornings through Aug. 31.
Aug. 25: Venus and Jupiter are within 1.8 degrees.
Aug. 26: Venus and Jupiter are within 0.8 degrees.
Aug. 27:This is the first evening Jupiter appears to the lower right of Venus. The planets are just 0.2 degrees apart, as seen from California—and about 0.1 degrees apart from the Eastern U.S. Alert your friends in that part of the country! Mercury, faded to magnitude +0.8, appears 5.1 degrees south (to the lower left) of the bright pair, and may be missed.
Aug. 28: Venus and Jupiter are 1.2 degrees apart. Their separation increases by about 1 degree daily. Venus and Mercury are 5 degrees apart, the minimum distance for this passage.
Aug. 31: Venus and Jupiter are 4.3 degrees apart, with Jupiter getting lower each evening. On what date will you last spot Jupiter?
Sept. 1: The new moon occurs at 2:03 a.m.
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 did graduate work in planetarium science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.