August opens with bright Mars in the sky nearly all night, setting about 45 minutes before sunrise. It is just past its perihelic opposition and closest approach. Watch Mars dim in brightness and diminish in size as our planet pulls away from its outer neighbor. Mars, the second brightest planet, shines 4° above the southeast horizon during early evening twilight. The other three bright planets – Venus, Jupiter, and Saturn – are farther west. Mercury still has an eastern (evening) elongation, but it sets only 8 minutes after the sun. This speedy planet is headed for its inferior conjunction early in the month. At Nautical Twilight, 70 minutes after sunset, brilliant Venus, approaching its greatest elongation, is in the west between Regulus and Spica, 29° to Spica’s lower right. Watch Venus close the gap with Spica during the month. It is on a shorter and faster solar orbit. Venus is slowly catching Earth in the same way Earth caught and passed Mars. (From Mars, Earth just passed what we call inferior conjunction for Earth’s inner planets.) Jupiter is in the south-southwest in Libra, near Zubenelgenubi. Saturn, above the Teapot of Sagittarius, is in the south-southeast as the sky darkens. For the summer season the change of the length of daylight is noticeable during the month. At the beginning of August, the sun is in the sky for 14 hours, 25 minutes. With twilight, the dawn to dusk time is 18 hours, 13 minutes. By month’s end daylight is reduced to 13 hours, 10 minutes and 16 hours, 38 minutes with the three phases of twilight. Here are the highlights for the beginning of the month:
- August 1: It’s Perseid Meteor Shower showtime! The shower’s peak display occurs during the moon’s New phase this year. The meteors appear to emerge from a point in space (radiant), much like the effect of falling snowflakes when you drive through a snowstorm. During the shower period, Perseids can be seen anywhere in the sky, at any time of the night. Some meteors are flashes that catch your eye, while others are brighter, leaving a train that persists for a short time. Trace the path of the meteor backward toward Perseus to determine whether it’s a Perseid or a sporadic meteor (not associated with the shower). When reversing the track, the random meteor’s origin is in another part of the sky. The highest meteor counts occur as the radiant approaches the zenith after midnight and before the beginning of morning twilight. To get a maximum meteor count, watch in a group of five observers, four looking above each cardinal point and one looking toward the zenith. Cut the official estimates in half if you’re observing in or near town, because many of the meteors are dim; yet, others are bright and impressive to see. Divide the predicted rate by 5, if you’re observing alone. It is important to note that the predicted rates for all meteors visible are across the entire sky, not visible to an individual observer. After midnight on the peak mornings, we see the meteoroids’ orbits nearly head on. So, at prime times, lone observers may see 10 meteors per hour in a dark location, 5 per hour in town. This evening, Venus sets at Astronomical Twilight (sun’s altitude is −18°), 150 minutes after sunset. For the remainder of the apparition, Venus sets during twilight.
- August 4: The moon is at its Last Quarter phase, 1:18 p.m. CDT.
- August 6: In the morning near the time of Astronomical Twilight, about 2 hours before sunrise, the waning crescent moon is 5.1° from Aldebaran. The star is 28° up in the eastern sky. The moon is 1.2° above Gamma Tauri, in the Hyades star cluster. Take in the view of the moon and star cluster with binoculars. In the evening sky, Jupiter is 90° east of the sun. One hour after sunset, it’s 23° up in the southwest, about 1° to the upper right of Zubenelgenubi.
- August 7: Have you looked for Perseids? If you wait long enough, you’ll see a few.
- August 8: At 2 hours before sunrise, the waning crescent moon is 13° up in the east-northeast. While not in the best observing location, use binoculars to note that the moon is 4.6° to the lower left of the star cluster M35. Mercury is at its inferior conjunction, 9:06 p.m. CDT.
- August 9: Start looking for Sirius about 45 minutes before sunrise for its first appearance in your morning sky before sunrise, its helical rising date. You’ll need a clear southeast horizon as Sirius appears only about 4° above the horizon at this first appearance. “Dog Days” may be associated with the helical rising of Sirius. It is coincidence is this occurs during the hot, humid days of August.
- August 10: While the moon is near its new phase, visit a remote location, even for a short visit, to see the Milky Way arching across the sky from north to south. Look for the bright nebulae and star clusters in the southern region in Sagittarius and surrounding regions, the Sagittarius Star Cloud, and the Scutum Star Cloud. Be sure to check out the dust clouds of the Great Rift, nearly overhead in Cygnus and follow it southward as it breaks the glow of the Milky Way into two parts. Some of my favorite August targets are the Ring Nebula, Epsilon Lyrae, Albireo, mainly because the double stars are celestial gems to show to new observers. Albireo’s contrasting star colors always impress beginning sky watchers. With binoculars, look for the “Double Cluster” h Persei and χ Persei.
- August 11: The moon is at its New phase at 4:58 a.m. CDT. There is a partial solar eclipse visible from north and eastern Europe, northern parts of North America, and northern and western parts of Asia.
- August 12: Look for Perseids after midnight and before morning twilight begins.
- August 13: This year’s peak Perseid rate may occur this morning according to NASA’s meteor expert Bill Cooke, cited in a space.com article (https://tinyurl.com/yb7ww7lh).
- August 14: At mid-twilight (75 minutes after sunset, sun’s altitude is -9°), Venus is 4° up in the west. The waxing crescent moon is 6.6° to the upper left of Venus. Gamma Virginis is about 2° to the lower right of the moon, and nearly 5° to the upper left of Venus. Spica is 16° to the upper left of Venus.
- August 15: At mid-twilight (60 minutes after sunset), Spica is 9° up in the west-southwest, with the waxing crescent moon (4.7 d, 27%) 6.5° above the star. The Venus-Spica gap is 15°.
At mid-month at evening Nautical Twilight (75 minutes after sunset), the four bright planets span the sky from east to west, ranging from Mars in the southeast, Saturn in the south, Jupiter in the southwest, and Venus low in the west. Venus is near its greatest elongation. Watch Venus close the gap with Spica for a widely-spaced conjunction at month’s end. In the morning dim Mercury, only 11° west of the sun, is moving toward a favorable morning greatest elongation at month’s end. Now, though, it is quite dim, but watch it brighten about 30 times during the next two weeks. Continue to look for Perseid meteors. Here’s what’s up during the second half of the month:
- August 16: Jupiter, 18° up in the southwest at mid-twilight (50 minutes after sunset), passes 0.5° from Zubenelgenubi. This is the third conjunction during Jupiter’s apparition. The waxing crescent moon is 7° to the right of Jupiter.
- August 17: Venus reaches its greatest elongation (45.9°), 70 days before its inferior conjunction. The thick waxing crescent moon is 6.6° to the upper left of Jupiter. Slow-moving Jupiter remains close to Zubenelgenubi, 0.6° this evening. Watch the gap widen during the next several weeks as Jupiter creeps eastward.
- August 18: The moon is at its First Quarter phase, 2:49 a.m. CDT.
- August 19: At mid-twilight, Antares stands 18° up in the south-southwest with the waxing gibbous moon 10° to the upper left of the star and 16° to the right of Saturn.
- August 20: The Venus-Spica gap is 10°. Venus is 32° to the lower right of Jupiter. This evening, the waxing gibbous moon is 3.9° to the right of Saturn.
- August 21: This evening, the waxing gibbous moon is 8.1° to the left of Saturn, 25° up in the south during mid-twilight.
- August 22: The moon (11.7 d, 90%) is 8.8° to the upper right of Mars.
- August 23: At 30 minutes before sunrise, Mercury, 8° up in the east-northeast, 21° below Pollux and 22° to the lower left of Procyon. During the next two weeks, look for Mercury far below Pollux. The gap between them grows about 0.5° each day. Have you looked for Sirius during morning twilight? In the evening sky, the moon is 8° to the upper left of Mars.
- August 24: What is the last date that you see a Perseid meteor?
- August 26: Mercury is at its morning greatest elongation. The separation from the sun is only 18.3°, but the ecliptic has a 25-degree inclination, favorable for locating Mercury. Mercury rises 90 minutes before sunrise in the east-northeast. Look for it with binoculars 23° below Pollux. The moon is Full at 6:56 a.m. CDT. In the evening sky the Venus-Spica gap is 5°.
- August 27: Mars’retrograde ends this evening near the kite-shaped asterism Dog’s Country. The group made of Omega Sagittarii, 59 Sagittarii, 60 Sagittarii, and 62 Sagittarii. Tonight, Mars is 2.6° from Omega Sagittarii.
- August 31: Venus passes 1.2° below Spica. After this conjunction, Venus sets much earlier each evening, nearly mirroring the setting time of Spica. They disappear into bright twilight together, not setting more than about 15 minutes apart as they head toward their respective solar conjunctions. This evening Venus is 24° to the lower left of Jupiter.
As the month ends, the summer planet parade begins to lose its brightest planet. Now setting 85 minutes after sunset, Venus is heading toward its phase of greatest brightness. Through a telescope, Venus displays a thick evening crescent phase that is 29.5” across. With Venus near Spica, the pair begins to descend into evening twilight. Speedy Mercury, now fading from the morning sky, is moving toward its superior conjunction late in September. Jupiter, visible in the southwest in Libra east of Zubenelgenubi, appears to be heading toward an evening conjunction with Venus. Watch what occurs next month. Saturn, slowest moving among the other brighter planets in the planet parade, begins the evening in the south. Spectacular Mars, shining in the sky nearly all night, starts the evening in the south-southeast. The moon rises in the east around 10:30 p.m. When did you first see Sirius in the pre-sunrise sky? How many Perseids did you see? Did you check your star charts to determine the Perseids’ radiant location? Did you observe the Milky Way?