The lone bright planet of August evenings shows more in a telescope than all the others combined.
Planet-watchers in August have one bright planet beckoning in the south at nightfall — Jupiter — and one high in the south around daybreak: Mars. The brightest planet, Venus, slips down out of the sunset sky and then, late in the month, emerges back into view before sunrise.
Jupiter is the first "star" you’ll see coming out on August evenings, burning brighter and brighter in the south as darkness deepens. Sparkling just 5° below it is golden-orange Antares, heart of the Scorpion, 1/20th as bright. In August Jupiter halts its retrograde (westward) motion against the stars and begins moving back eastward just before it can achieve a conjunction with Antares. But its motion is slow and slight, so use binoculars to note its changing position among the stars from night to night.
Telescopically, Jupiter's disk shrinks from 42″ to 38″ wide in August as Earth pulls away from it in our faster orbit around the Sun. But that’s still large enough to afford good views of details in its ever-changing dark belts and bright zones during moments of steady atmospheric seeing.
The asteroid Vesta, magnitude 7.2, passes 0.4° north of Jupiter on the evening of August 29th for the Americas.
Pluto is also in the south at nightfall, about 17° to Jupiter’s east-northeast. You can locate the controversial, 14th-magnitude speck with a 10-inch or larger telescope and a detailed finder chart.
There you’ll also find charts for spotting much easier Neptune (8th magnitude) and Uranus (6th magnitude) later in the night. Neptune, in Capricornus, reaches opposition on August 13th, so it’s highest in the middle of the night. A good telescope will show its pale blue-gray disk, just 2.3″ wide, as a nonstellar blob. Uranus, 3.6″ wide in Aquarius, appears to some people very pale gray-green. This year Uranus trails Neptune by about an hour and a half in their late-night journey across the sky.
Mars rises around 1 a.m. daylight-saving time at the beginning of August, and around midnight by month’s end. The brightening, fire-hued planet passes 5° to the lower right of the Pleiades on the morning of August 7th. Two weeks later it’s skimming just north of the northern arm of the Hyades V. On August 22nd Mars passes 4½° north of Aldebaran. They’re almost identical in color, but by then Mars is nearly twice as bright as Aldebaran (they’re magnitudes +0.3 and +0.9, respectively).
Mars is still tiny in a telescope, growing from 7″ to 8″ in August. Mars will be nearly 16″ wide around its late-December opposition.
Mercury is still visible before sunrise as August begins, but it quickly drops out of sight and reaches superior conjunction with the Sun on August 15th.
Saturn is in conjunction with the Sun on August 21st and remains out of sight all month. This is a shame, because Saturn and Mercury pass less than ½° apart on August 18th, when they’re only 3° from the Sun.
August 18th is the same day Venus is in conjunction with the Sun. This is its inferior conjunction — when it’s on the near side of its orbit to us and passing closer than any other planet can — so it races through this position and shoots up to shine low in the dawn hardly more than a week later.
Actually, Venus is so bright that at the start of August, pre-conjunction, you can try glimpsing it very low in the west shortly after sunset. At month’s end, look for it low in the east before sunrise. Throughout this period Venus is a very thin, long crescent, as shown on page 42. Get a telescope on it if you can.
The Moon is a thick waning crescent when it appears about 8° left of Mars before dawn on August 7th (for North America). New Moon occurs on August 12th, leaving skies dark for the peak of the Perseid meteor shower late that night. The Moon is just past first quarter when it glides close below Antares and Jupiter on the American evening of August 21st — one week before the full Moon undergoes its second total eclipse of the year.
Speaking of which, the big event this month for much of the world is the total eclipse of the Moon on August 28th. Centered on the Pacific, its visible from a little more than half the globe — including much of North America at dawn and East Asia at dusk. Totality is long (91 minutes) and deep, so the Moon will probably get rather dark around mid-eclipse (3:37 a.m. PDT).
Moon Phases
Last Quarter: Aug. 5, 5:20PM ET
New Moon: Aug. 12, 7:03PM ET
First Quarter: Aug. 20, 7:54PM ET
Full Moon: Aug. 28, 6:35AM ET
Other Sky Highlights
Aug. 5: Mars passes 5° south of the Pleiades in the morning sky
Aug. 12: Perseid meteors peak late tonight
Aug. 13: Neptune is at opposition
Aug. 18: Venus is in inferior conjunction, passing 8° south of the Sun
Aug. 28: Total lunar eclipse before dawn for the Americas
Aug. 29: Vesta (magnitude 7.2) passes 0.4° north of Jupiter tonight
© 2007 Reprinted with permission from Sky Publishing Corp.