The cornucopia of astronomical treats this month includes two “super” moons and one “blue” moon; evening twilight moonrises Aug. 1-3 and Aug. 30-Sept. 2; spectacular views of the Milky Way during the moon’s absence in the first hour after nightfall Aug. 6-19; the moon uncovering Antares Aug. 24; and Saturn rising in early evening.
Late-night and early-morning morsels include prime moonless views of the Perseid meteor shower; a star masquerading as a satellite of Jupiter; a rich, star-filled eastern predawn sky; and a supersized Venus crescent rocketing up from the horizon day by day in late August.
At the start of August, Venus sets very soon after sunset, too early to appear on our evening mid-twilight map. By late in August, Saturn becomes visible in the evening twilight, low in the east-southeast, joining a half-dozen bright stars already present and well seen: The Summer Triangle of Vega, Altair and Deneb high in eastern sky; Arcturus, the “Bear-watcher” star, high in west-southwest, with Virgo’s Spica 33 degrees to its lower left; and Antares, heart of the Scorpion, crossing through south to south-southwest. Left of the Scorpion is the Teapot asterism within Sagittarius, the Archer. The Milky Way star clouds look like steam issuing forth from the Teapot’s spout, whose top two stars mark the arrow aimed just below the Scorpion’s heart. Faint Mars and fading Mercury, low in bright twilight in the west, will be a serious challenge, requiring binoculars.
Saturn reaches opposition on the night of Aug. 26-27, as Earth passes between the sun and Saturn. The ringed planet is then visible all night; find it low in the east-southeast at dusk, high in the south in middle of night, and low in the west-southwest at dawn. A telescope reveals the rings tipped 9 degrees from edgewise, closer to edge-on than at Saturn’s oppositions in recent years.
On Aug. 1, Saturn is 6.4 degrees west-southwest of 3.8-magnitude Lambda Aquarius and retrograding. At the end of evening twilight on Aug. 31, Saturn is 8.5 degrees west-southwest of Lambda Aqr, 4.4 degrees east-northeast of Iota Aqr, and 9.6 degrees east-northeast of 2.9-magnitude Delta Cap.
As the month begins, the Summer Triangle is sinking in the west to northwest in morning twilight. Jupiter, high in southeast, remains the brightest morning “star,” but it soon gets competition. During the second week, the “Dog Star” Sirius begins to appear above the east-southeast horizon, below and in line with the Belt of Orion, which is midway between Rigel and Betelgeuse, but not plotted on the chart. Sirius is the brightest nighttime star, but falls short of Jupiter’s current brilliance by a full magnitude. Sirius, Procyon and Betelgeuse form the Winter Triangle. If you can spot Sirius while it is still low in the sky, turn around and catch Altair about to set just north of west. If you can spot Sirius before Altair sets, then you can see both the Summer and the Winter Triangle simultaneously!
Look 1 1/2 to 2 hours before sunrise, in the darkness before dawn, and you’ll be struck by the number and beauty of bright stars visible in the eastern sky. Extend Orion’s belt away from Sirius, upward past Aldebaran and the Hyades star cluster, forming the V-shaped head of Taurus, the Bull, and onward to the compact Pleiades, or Seven Sisters star cluster. These are wonderful subjects for binocular viewing! Look also for the Great Nebula in the Sword of Orion.
Halfway between Orion’s belt and the North Star is Capella, the “Mother Goat” star, rising high in the northeast. Below Capella and rising higher to the left of Orion in August’s morning skies are Pollux and Castor, the “Twin” stars of Gemini, just 4 1/2 degrees apart.
It should be an excellent year for the Perseid meteor shower. Peak activity is expected in the predawn darkness hours of Aug. 13. Meteors can light up anywhere in the sky, but what all members of this shower have in common is that their tracks, extended backward, will radiate from a point in the constellation Perseus, below the “W” of Cassiopeia in the northeast. The moon will be just a thin crescent, rising less than three hours before sunrise, so will not interfere with viewing.
Distant Uranus and Neptune are easy to locate in the late night to predawn skies this month. Uranus, near magnitude 5.7, is easily picked up with binoculars 2.7-2.9 degrees southeast of 4.3-magnitude Delta in Aries and will commence retrograde on Aug. 31. Neptune, of magnitude 7.8 and so more of a challenge, is already in retrograde, conveniently very close to the 5.5-magnitude star 20 in Pisces. Through binoculars, look southeast of the Circlet of Pisces and northwest of Iota Ceti for a compact, six-star asterism we’re calling Neptune’s Dipper.
Look near Jupiter for 5.5-magnitude Sigma in Aries at the start of morning twilight. Note also 5.8-magnitude Omicron Ari 1.7 degrees west of Sigma. The 5.3-magnitude star Pi Ari forms an isosceles triangle with Sigma and Omicron, to their north, and 2.4 degrees from each. This triangle will help the viewer notice small changes in the position of Jupiter.
On Aug. 1, Jupiter is 1.5 degrees west-southwest of Sigma Ari. By Aug. 7, Jupiter closes the distance to 1 degree. On Aug. 8, Jupiter is equidistant from both Omicron and Sigma Ari, 0.9 degrees from each. On Aug. 13, Jupiter is 0.5 degrees west-southwest of Sigma Ari. On Aug. 21, Jupiter is 1.3’ (arcminutes) from Sigma Ari at start of a.m. twilight, and still just 1.1 degrees from Sigma Ari one hour after Jupiter rises in late evening on Aug. 21. On Aug. 22, Jupiter is 1.6 degrees from Sigma at start of morning twilight.
Is that an extra Galilean moon of Jupiter? For several mornings, Aug.18-26, Jupiter may seem to have a fifth Galilean moon, actually the 5.5-magnitude star Sigma Ari.
Getting back to morning sky at mid-twilight: Closer to sunrise, Venus first appears above the horizon, just north of east, around Aug. 22. Venus then outshines Jupiter by nearly two magnitudes, but for its first several days, the twilight glow will make Venus seem less bright than it is. Once Venus becomes visible, you can see the morning lineup of three bright planets: Venus, low, north of east; Jupiter, high in south; and Saturn, low in west-southwest.
Keep track of Venus daily as sunrise approaches. Telescopes, and even a pair of binoculars, will reveal Venus’ crescent phase, changing from 4 percent illuminated and 16 degrees to the upper right of rising Sun on Aug. 22, to 11 percent and 26 degrees to the upper right of the sun on the 31st.
This month, the moon is full twice, on Aug. 1 and again on Aug. 30. Both full moons occur near the moon’s perigee, when it’s closest to Earth, so expect much trumpeting in the media about “super moons.” Further, the second full moon in the same calendar month is sometimes (incorrectly) called a “blue moon.” We’ll have a genuine blue moon as originally defined—the third full moon of an astronomical season with four—on Aug. 19, 2024.
Since the full moon is at opposition to the sun, rising around sunset and setting around sunrise, watch for Saturn near the moon, from nightfall on Aug. 2 until dawn on Aug. 3, and again during all the darkness hours on the nights of Aug. 29 and 30.
Here is a listing of the moon’s encounters with other naked-eye planets and prominent stars.
Predawn: Aug. 8, last quarter (half full), near Jupiter.
Aug. 9, fat crescent, near the Pleiades (Seven Sisters) star cluster.
Aug. 10, waning crescent near Aldebaran and the Hyades cluster.
Aug. 13, a thin crescent to the right of Pollux and Castor, the Twins; below them the next morning.
Aug. 15, a very challenging 1 percent old crescent moon, 2-3 degrees up in the east-northeast, 32 minutes before sunrise; less than 10 degrees from the sun.
In early dusk on Aug. 17, using binoculars 40 minutes after sunset, try for the 3 percent young crescent moon, nine degrees north of west and only 3-4 degrees up. Can you spot faint Mars, 11 degrees to the moon’s upper left? How about Mercury, 9 degrees to the lower left of the moon, and 5.3 degrees to the lower right of Mars?
Aug. 18, 40 minutes after sunset, the 7 percent crescent should be easy for the unaided eye in clear, unobstructed skies. Use optical aid for faint Mars, about 1 degree below, and fading Mercury, 5.5 degrees to the lower right of Mars.
Aug. 20, one hour after sunset, the 19 percent moon is easy, low in the west-southwest, with Spica 5 degrees to the left. On the next evening, the 28 percent moon will be 7-8 degrees to Spica’s upper left.
On Aug. 24, the 57 percent gibbous moon occults, or covers Antares. The event will occur in daylight or bright twilight from western U.S., so a telescope will be required.
From Reno, the advancing dark edge of the moon snuffs out the star shortly before 6:40 p.m., more than an hour before sunset. The star reappears along the illuminated edge of the moon, more than halfway from the southern cusp (the lower point of the crescent) to its midpoint, at 7:39 p.m., as the sun is about to set. As the moon moves away from Antares, and the sky darkens, the star will become easier to observe. By 9:11 p.m., the moon will have moved its own diameter to the east of the star.
Robert Victor originated the Abrams Planetarium monthly Sky Calendar in October 1968 and still helps produce an occasional issue. He enjoys being outdoors sharing the beauty of the night sky and other wonders of nature.