Sunday, Aug. 1 — Crescent moon near Uranus (before dawn)
When the waning crescent moon rises in the Americas at about 12:30 a.m. local time on Sunday morning, Aug. 1, it will be positioned several finger widths below (or 3.5 degrees to the celestial southeast) of the magnitude 5.8 planet Uranus. Early risers in Europe and Africa will see the pair closer together. While Uranus can normally be seen easily in binoculars (red circle), note its location between the stars of Aries and Cetus, and look for it on a night when the bright moon has moved away.
Sunday, Aug. 1 — Double shadow transit and Jupiter's Great Red Spot (1009-1020 GMT)
On the morning of Sunday, Aug. 1, observers with telescopes in the western half of North America and the Pacific Ocean region can see a rare event on Jupiter! At 3:30 a.m. CDT (0830 GMT) the Great Red Spot will join the round black shadow cast by Jupiter's moon Ganymede while it is crossing Jupiter's disk. At 5:09 a.m. CDT (1009 GMT), Europa's smaller shadow will join them. About 12 minutes later, Ganymede's shadow will complete its transit and disappear, leaving the GRS and Europa's shadow to cross until about 8 a.m. CDT (1300 GMT). In more easterly time zones, the sun will rise before the event has ended.
Monday, Aug. 2 — Saturn at opposition (all night)
During the wee hours of Monday, Aug. 2 in the Americas, Saturn will reach opposition among the stars of central Capricornus. Objects at opposition are visible all night long — rising at sunset and setting at sunrise — because Earth is positioned between them and the sun. At opposition, Saturn will be at a distance of 830.6 million miles, 1.337 billion km, or 74.3 light-minutes from Earth, and it will shine at magnitude of 0.18 — its brightest for 2021. While planets at opposition always look their brightest, Saturn's peak magnitude 0.18 will be enhanced by the Seeliger effect, backscattered sunlight from its rings. In a telescope (inset) Saturn will show an apparent disk diameter of 18.6 arc-seconds, and its rings will subtend 43.3 arc-seconds. Saturn's rings will be tilting more edge-on to us every year until the spring of 2025. This year they are already closed enough for Saturn's southern polar region to extend beyond them. Opposition is also a fine time to view a handful of Saturn's moons with a backyard telescope in a dark sky.
Wednesday, Aug. 4 — Juno stands still (overnight)
On the night of Wednesday, Aug. 4, the main belt asteroid designated (3) Juno will complete a westerly retrograde loop across the stars of central Ophiuchus. After standing still tonight, it will return to traveling prograde eastward. To see the magnitude 10.7 object, aim your telescope 2.3 degrees above and between the bright stars Saik and Yed Posterior, which outline the lower right (southwestern) corner of the Serpent-Bearer's body.
Friday, Aug. 6 — Milky Way star clusters (all night)
With the moon approaching its new phase, this weekend's darker evenings will be ideal to explore the countless knots and clumps of stars distributed along the Milky Way, many of which were included in Charles Messier's list of the sky's best deep sky objects. Scan with binoculars to spot the objects, and then follow up with a backyard telescope at low magnification. Particularly good clusters include Messier 39 and Messier 29 in Cygnus, Caldwell 16 in Lacerta, the Wild Duck cluster (Messier 11) and Messier 26 in Scutum, and the Sagittarius Star Cloud (Messier 24).
Sunday, Aug. 8 — Double shadow transit on Jupiter (1245-1420 GMT)
In the wee hours of Sunday, Aug. 8 observers with telescopes in the Pacific Ocean and Eastern Asia regions can see the round, black shadows of two of Jupiter's moons drift across that planet together. At 12:45 a.m. Hawaiian Standard Time (1045 GMT), Ganymede's shadow will begin to follow the Great Red Spot across Jupiter. At 2:45 a.m. HST (1245 GMT), Europa's smaller shadow will begin to cross. Ganymede's shadow will move off the planet at 4:20 a.m. HST (1420 GMT). Europa's shadow will complete its transit an hour later, just as the Ganymede itself clears Jupiter's limb.
Sunday, Aug. 8 — New moon (1350 GMT)
The moon will reach its new phase on Sunday, Aug. 8 at 9:50 a.m. EDT (1350 GMT). While new, the moon is traveling between Earth and the sun. Since sunlight can only reach the far side of the moon, and the moon is in the same region of the sky as the sun, the moon becomes unobservable from anywhere on Earth for about a day (except during a solar eclipse). After the new moon phase Earth's planetary partner will return to shine in the western sky after sunset.
Tuesday, Aug. 10 — Crescent moon near Venus (after sunset)
Look just above the western horizon after sunset on Tuesday, Aug. 10 to see the young crescent moon shining a palm's width to the right (or 6.5 degrees to the celestial northwest) of the extremely bright planet Venus. On the following evening, the orbital motion of the moon will shift it a similar distance to Venus' upper left (celestial east). During August, the greatly tilted ecliptic (green line) will prevent Venus from climbing very high for mid-Northern latitude skywatchers.
Thursday, Aug. 12 — Perseid Meteor Shower peak (predawn)
The spectacular Perseid meteor shower, which runs between July 17 and 26 every year, will peak during mid-day in the Americas on Thursday, Aug. 12. That means that the best time for seeing the most Perseid meteors in North America will be the hours before dawn on Thursday morning, when the shower's radiant in Perseus will be highest in the northeastern sky. This is the most popular shower of the year, delivering up to 100 meteors per hour at the peak. Derived from debris dropped by Comet Swift-Tuttle, many Perseids are extremely bright and leave persistent trails. Although fewer meteors are seen before and after the peak, skywatchers can also expect to see plenty of meteors on Wednesday, Thursday, and Friday night. To enjoy meteor showers, find a safe rural location with plenty of open sky and just look up. This year, the young crescent moon will set shortly after sunset on the peak date — leaving the whole night dark for meteor-watching.
Sunday, Aug. 15 — Three shadows dance across Jupiter (1442-1820 GMT)
On the evening of Sunday, Aug. 15 observers with telescopes across Asia can watch three of the small black shadows cast by Jupiter's moons as they cross the planet's disk in a complex dance. At 11:42 p.m. Japan Standard Time (1442 GMT), Ganymede's shadow will move onto Jupiter, joining Callisto's shadow. They'll appear together for about 10 minutes until Callisto's shadow completes its own transit at 11:52 p.m. JST. At 12:08 a.m. Ganymede itself will begin to move onto Jupiter, and at 12:16 a.m. JST (1316 GMT) Europa's smaller shadow will appear at Jupiter's limb. The two shadows will cross Jupiter until 3:20 a.m. JST (1820 GMT). In the meantime, Europa's faster-moving shadow will overtake and merge with Ganymede's shadow for several minutes surrounding 2:24 a.m. JST (1724 GMT).
Sunday, Aug. 15 — First quarter moon (1519 GMT)
When the moon completes the first quarter of its journey around Earth on Sunday, Aug. 15 at 11:19 a.m. EDT (1519 GMT), its 90-degree angle away from the sun will cause us to see the moon half-illuminated — on its eastern side. At first quarter, the moon always rises around midday and sets around midnight, so it is also visible in the afternoon daytime sky. The evenings surrounding first quarter are the best ones for seeing the lunar terrain when it is dramatically lit by low-angle sunlight, especially along the terminator, the pole-to-pole boundary between the lit and dark hemispheres.
Wednesday, Aug. 18 — Mercury just misses Mars (after sunset)
On Wednesday, Aug. 18, the rapid eastward orbital motion of Mercury (red path) will carry it very closely past Mars, allowing both planets to share a blurry eyepiece view in a backyard telescope (red circle) — but use optics only after the sun has completely set. Magnitude -0.46 Mercury will be eight times brighter than Mars. On Wednesday, Mercury will be located 9 arc-minutes to the lower right (southwest of) the red planet. The following evening, look for Mercury positioned 1 degree to Mars' upper left. This conjunction will not be seen easily at mid-northerly latitudes; but observers in the southern USA and farther south can see the pair in a darker sky, sitting just above the western horizon before they set at 8:45 p.m. local time.
Friday, Aug. 20 — Jupiter at opposition (all night)
On Friday, Aug. 20, Jupiter will reach opposition among the stars of eastern Capricornus. Since Earth will be positioned between the sun and the gas giant on that date, Jupiter will rise at sunset, remain visible all night long, and set at sunrise. At opposition, Jupiter will be 373.1 million miles, 600.4 million km, or 33.3 light-minutes from Earth, and it will shine at its maximum brightness of magnitude -2.88 for 2021. Because Jupiter is approaching perihelion in January, 2023, the planet will sport a generous, 49 arc-seconds-wide disk at this year's opposition. Views of Jupiter in amateur telescopes (inset) will show its equatorial bands, and the Great Red Spot every second or third night. Around opposition, Jupiter and its four large Galilean satellites frequently eclipse and occult one another, and cast their round, black shadows on the planet — singly and in pairs.
Friday, Aug. 20 — Uranus pauses in Aries (overnight)
On Friday, Aug. 20, Uranus will cease its motion across the stars of southern Aries and prepare to commence a westward retrograde loop that will last until January, 2022. Tonight the magnitude 5.7 planet will rise shortly before 11 p.m. local time and remain visible until the predawn. Uranus will be surrounded by the 5th magnitude stars Sigma, Omicron, Pi, and Rho Arietis — creating a distinctive asterism for anyone viewing Uranus in binoculars (red circle).
Friday, Aug. 20 — Bright moon below Saturn (all night)
After the sun sets on Friday evening, Aug. 20, look towards the southeast for the bright waxing gibbous moon shining several finger widths below (or 4.5 degrees to the celestial south of) yellowish Saturn — with much brighter Jupiter positioned off to their left (east). As they cross the sky during the night, the moon and the ringed planet will (just barely) share the field of view of binoculars (red circle), and the diurnal rotation of the sky will lift the moon to Saturn's left. They'll set together in the west-southwest before dawn.
Saturday, Aug. 21 — Gibbous moon joins Jupiter and Saturn (all night)
After 24 hours of motion, the gibbous moon will hop east to sit below (south of) Jupiter and Saturn in the southeastern sky after dusk. The trio will make a lovely wide-field photo when composed with some interesting scenery. The moon will be somewhat closer to brighter Jupiter than Saturn — and just close enough for them to fit together in binoculars (red circle); but only until after midnight, because the moon's eastward orbital motion will draw it farther from the planet. By the time the moon drops below the west-southwestern horizon as the sun is rising (another photo opportunity), it will have shifted to Jupiter's left.
Sunday, Aug. 22 — Full Green Corn Moon (1202 GMT)
The August full moon will occur on Sunday, Aug. 22 at 8:02 a.m. EDT or 12:02 GMT. This full moon, colloquially called the "Sturgeon Moon," "Red Moon," "Green Corn Moon," and "Grain Moon," always shines among or near the stars of Aquarius or Capricornus. The indigenous Anishinaabe people of the Great Lakes region call this moon Manoominike-giizis, the Wild Rice Moon, or Miine Giizis, the Blueberry Moon. The Cree Nation of central USA and Canada calls the August full moon Ohpahowipîsim, the Flying Up Moon. The Haudenosaunee (Iroquois) of Eastern North America call it Seskéha, the Freshness Moon. The moon becomes fully illuminated because it is opposite the sun in the sky, causing the moon to rise at sunset and set at sunrise. Since the full phase will officially occur on Sunday morning in the Americas, the moon will appear to be full on both Saturday night and Sunday night. But magnified views will reveal a thin strip of darkness along the moon's western and eastern limbs on Saturday and Sunday night, respectively.
Sunday, Aug. 22 — Europa and Ganymede shadows on Jupiter (1842-2040 GMT)
On Sunday night, Aug. 22, observers with telescopes across Eastern Europe, eastern Africa, and Asia can watch the small black shadows of two of Jupiter's moons cross the planet's disk at the same time. At 8:42 p.m. Central European Standard Time or 18:42 GMT, Ganymede's large shadow will join Europa's smaller shadow already crossing. The two shadows will appear together for two hours until Europa's shadow moves off at 10:40 p.m. CEST, or 20:40 GMT, leaving Ganymede's shadow to complete its transit at 12:20 a.m. CEST or 22:20 GMT. In eastern Asia, the double shadow event will be observable during the wee hours of Monday morning.
Wednesday, Aug. 25 — Double stars in Lyra's parallelogram (all night)
Each corner of Lyra's parallelogram is marked by a double star. Zeta Lyrae (ζ Lyr), the corner closest to bright Vega, can be split with binoculars. Both components are white — one star slightly brighter than the other. Each of these stars also has a partner that is too close together to split visually. Moving clockwise, the southwest corner star is Sheliak, the brightest of a tight little grouping of stars visible in a telescope. Sheliak itself has a close-in, dim companion in an eclipsing binary system with a 13 day period. The hot, blue giant star Sulafat sits at the farthest corner from Vega. 620 light-years-distant Sulafat is much larger than Vega — an old star on its way to becoming an orange giant many years from now. Add the slightly dimmer stars Lambda Lyrae and HD 176051 to its south and west, respectively to form a naked-eye triple. Delta Lyrae (δ Lyr) marks the northeast corner of the parallelogram. Sharp eyes and binoculars will easily split the double into one blue and one red star. The blue star is one hundred light-years farther away than the red one; they just happen to appear close together along the same line of sight.
Friday, Aug. 27 — The Teapot tilts west (evening)
Moonless August evenings are ideal for viewing the deep sky objects near one of the best asterisms in the sky, the Teapot in Sagittarius. This informal star pattern features a flat bottom formed by the stars Ascella on the left (east) and Kaus Australis on the right (west), a pointed spout on the right (west) marked by the star Alnasl, and a pointed lid marked by the star Kaus Borealis. The stars Nunki and Tau Sagittarii form a handle on the left-hand (eastern) side. The bent line of three stars named Kaus — Borealis (north), Meridianalis (center), and Australis (south) — refer to the archer's bow. The asterism reaches maximum height above the southern horizon before 10 p.m. local time, when it will look as if it's serving its hot beverage — with the Milky Way representing rising steam.
Friday, Aug. 27 — Bright moon near Uranus again (overnight)
For the second time this month, the bright, waning gibbous moon will pass close to Uranus. After the moon has climbed high enough to become visible above the treetops late on Friday evening, Aug. 27, look for the magnitude 5.8 planet sitting several finger widths to its upper left (or 3.5 degrees to the celestial northeast) — close enough for them to share the view in binoculars (red circle). While the blue-green dot of Uranus can be seen in binoculars, it's a good idea to note its location between the stars of Aries and Cetus and hunt for it on a night when the bright moon has moved away.
Sunday, Aug. 29 — Two shadows and the Great Red Spot cross Jupiter (2242-2317 GMT)
Starting in late evening on Sunday, Aug. 29, telescope-users in the United Kingdom, Europe, and Africa can watch the Great Red Spot and the shadows of Jupiter's moons Europa and Ganymede cross Jupiter together. At 11:42 p.m. British Standard Time or 22:42 GMT, Ganymede's large shadow will appear along Jupiter's edge, not far from the Great Red Spot. Meanwhile, Europa's smaller shadow will be completing its own passage. The trio will remain visible until Europa's shadow moves off Jupiter at 12:17 a.m. or 23:17 GMT. Observers in the eastern part of South America can view the same event after local dusk.
Monday, Aug. 30 — A second third quarter moon (0713 GMT)
When a lunar phase occurs in the first few days of a calendar month, it can re-occur at month's end. For the second time in August, the moon will reach its third quarter phase at 3:13 a.m. EDT or 07:13 GMT on Monday, Aug. 30. The ensuing week of moonless evening skies will be ideal for observing deep sky targets.