AUGUST 2022 Giant planet time
Midsummer observing means giant planets, with Jupiter and Saturn visible before midnight. Both planets offer hours of amazing views. Saturn is visible all night, while Jupiter rises a bit later. You might catch elusive Mercury in the early evening if you’re lucky. And the morning sky carries the glories of a growing Mars and a brilliant Venus.
Mercury modestly hugs the western horizon all month. It’s a favorable apparition for Southern Hemisphere observers but is more challenging for those in the Northern Hemisphere. On Aug. 3, soon after sunset, you’ll find it only 0.8° north of Regulus, although the pair sets within an hour of the Sun. Try 30 minutes after sunset to spot magnitude –0.5 Mercury 4° high; use binoculars to find fainter Regulus.
Mercury’s elevation after sunset doesn’t improve much as August progresses, although its elongation from the Sun increases. Mercury slides southward along the horizon. By Aug. 14, it fades to magnitude 0 and stands 5° high due west 30 minutes after sunset.
Mercury reaches greatest eastern elongation Aug. 27 and fades to magnitude 0.3
— difficult to see in bright twilight. Try spotting it in binoculars on the 28th and 29th, as a crescent Moon enters the scene. Mercury lies 9.5° left of the Moon on the 28th and 6.5° below the Moon on the 29th.
Saturn rises in the east soon before 9 P.M. local time on
Aug. 1. It reaches opposition Aug. 14, so it is visible all night. The best time to view the planet is when it is highest in the southern sky, around 1 A.M. local time (local midnight using daylight saving time). It briefly brightens to magnitude 0.2 midmonth and is unmistakable within Capricornus the Sea
Goat as the brightest object in this part of the sky.
You’ll find 3rd-magnitude Deneb Algedi (Delta [δ] Capricorni) near Saturn, 1.7° southeast of the planet as
August opens. Saturn’s retrograde motion is easy to spot as the ringed planet wanders slowly westward at about 0.5° per week. August’s Full Moon, also opposite the Sun in the sky, lies within 5° of Saturn overnight on Aug. 11/12, shortly before the Perseid meteor shower peaks.
It’s the best time of the year to view Saturn’s rings, since the planet is closest to Earth at opposition (824 million miles), rendering the planet and its ring system at their largest apparent size to Earth dwellers. Saturn’s disk spans 19" across the
equator, but only 17" from pole to pole — the planet’s somewhat flattened disk is now evident as the tilt of the rings reveals more of the southern polar regions.
The rings span nearly 43" across and 10" along the minor axis. Compare this year’s view to last summer’s, and you’ll notice the distinct change in ring tilt. By 2025, the rings will appear edge-on.
Titan, Saturn’s largest moon, is an easy target for small scopes. You’ll find it north of Saturn Aug. 5 and 21, and due south Aug. 13 and 29. On
Aug. 19, a field star slightly dimmer than Titan’s magnitude 8.5 appears southwest of the planet; don’t confuse it for the moon, which lies southeast.
Closer to the rings, 10th-magnitude Tethys, Dione, and Rhea orbit with periods ranging from two to five days.
Two-toned Iapetus’ leading hemisphere is dark, causing the moon to appear faint at eastern elongations (12th magnitude) and brighter at western ones (10th magnitude). This month, Iapetus is brightest Aug. 7, when it reaches western elongation 9' west of Saturn. It moves to superior conjunction early
Aug. 27 for U.S. observers.
Usually, Iapetus skims past the northern hemisphere of Saturn’s disk, but the current shallow tilt of its orbital plane causes an occultation instead. It’s a
challenging event, given the brightness of Saturn and its rings, combined with Iapetus’ paltry 11th-magnitude glow. Digital imaging is likely to best capture the event. Iapetus lies just above the rings and begins to disappear around 12:25 A.M. EDT Aug. 27 (late on Aug. 26 in all other U.S. time zones).
Other moons also undergo eclipses and transits across the planet’s disk; these will increase over the next few years.
Neptune is an easy binocular object at magnitude 7.7. It starts the month in southwestern Pisces, 5° due south of Lambda (λ) Piscium, the Circlet’s southeasternmost star. You can also home in on Neptune by looking 13.5° southwest of Jupiter. The region is best viewed starting a couple of hours after midnight, when Neptune rises above 35° altitude in the southeastern sky.
Through binoculars on
Aug. 1, you’ll find a star of similar brightness 0.4° to the planet’s east. Neptune’s motion carries it westward; on Aug. 31, the pair is 1° apart. A telescope will reveal the distant planet’s dim bluish disk, spanning a mere 2". Neptune reaches opposition in September.
Jupiter lies in northwestern Cetus. It rises in the hour before midnight on Aug. 1 and soon before 9 P.M. local time by the 31st. It moves westward each night. Jupiter shines a brilliant magnitude –2.7 most of the month and reaches magnitude –2.8 in the last week of August.
The giant’s apparent diameter spans 49" by late August. The best views are in the early morning hours, when the planet stands high in the southern sky. It lies due south at 53° altitude by 5 A.M. local time (an hour before sunrise) on Aug. 1, and by 3 A.M. on Aug. 31.
Small telescopes reveal parallel dark equatorial belts, while larger scopes show progressively more detail, tempered by local seeing conditions. The planet’s temperate zones contain many spots, including the Great Red Spot that features every alternate night on average. All these features move quickly across the planet’s face, carried by Jupiter’s roughly 10-hour rotation period.
The four Galilean moons orbit Jupiter every two to 16 days. Dual transits are fascinating to follow; a fine example occurs Aug. 15/16. Less than an hour after Jupiter rises in the Midwest, Io’s shadow begins a transit at 11:24 P.M. EDT. Io itself stands 19" east of the planet’s limb at this time. Also spot
Ganymede 36" east of Io — note this for later. Io is the innermost large moon and moves faster than more distant Ganymede. Beginning at 11:59 P.M. EDT, Ganymede’s shadow appears
southeast of Io’s shadow. Now two shadows race across the jovian cloud tops, but faster Io’s will stay well ahead. Io itself begins a transit 24 minutes later.
By 1 A.M. EDT (midnight CDT), Io has caught up with Ganymede’s shadow and passes it within 30 minutes. Io’s shadow departs the western limb of Jupiter at 1:38 A.M. EDT, followed just under an hour later by Io. Ganymede’s huge shadow lingers until just before 3 A.M. EDT. If you stay up another few hours, you’ll catch Ganymede itself beginning its transit at 4:09 A.M. EDT. It leaves by 5:39 A.M. CDT, just as twilight arrives in the Midwest.
Mars and Uranus rise together in Aries soon after midnight local time on Aug. 1. Mars is easy to find, shining at magnitude 0.2. Uranus is much fainter, requiring binoculars to spot at magnitude 5.8. Center Mars in your binoculars and you’ll find Uranus 1.4° north of the Red Planet. Its bluish hue will contrast nicely with Mars.
Uranus has become the target of advanced imagers in recent years, and some elusive cloud features can be captured using high-speed video.
Visually in a telescope, Uranus renders a 4"-wide featureless disk. A Last Quarter Moon ventures within 4° of Uranus the morning of Aug. 18.
Mars moves eastward and crosses into Taurus Aug. 9, while Uranus remains in Aries; already, 4.7° separate them. Mars treks 6° south of the Pleiades between Aug. 16 and
19. The 19th is also when the Last Quarter Moon catches up and lies less than 3° from Mars. In the predawn sky, telescopes might show the contrasting dark Syrtis Major and the bright Hellas basin on the tiny disk.
By Aug. 31, Mars stands 5.7° northwest of similarly orangered Aldebaran, the brightest star in Taurus.
Mars season is now upon us: The Red Planet grows in apparent size from 8" to 10" during August. By the time it reaches opposition in December, Mars will be nearly double this size
— smaller than recent years but the best for some time to come.
Venus is a brilliant morning star at magnitude –3.9 all month. On Aug. 1, it rises in Gemini two hours before the Sun. The planet crosses into Cancer on Aug. 10 and by
Aug. 17 stands just under 1° west of the Beehive Cluster (M44). Look for the pairing in binoculars about 4° high one hour before sunrise.
Catch the waning crescent Moon 6.5° northwest of Venus Aug. 25 before sunrise. Venus’ elongation from the Sun continues declining, reaching 14° by Aug. 31. Fortunately, its brilliance still renders it visible even in the bright dawn sky.
Through a telescope, Venus changes from a 93-percent-lit disk spanning 11" on Aug. 1 to 97 percent lit and 10" across on Aug. 31.