Mars spends August on the border between Capricornus and Sagittarius. The planet’s westward motion against this background carries it from the former into the latter constellation on the 24th, but it comes to a halt four days later and then slowly heads east.
This region remains visible all night in early August, climbing highest in the south shortly before 1 a.m. local daylight time. It reaches the same position by 10:30 p.m. in late August. Mars peaks at an altitude of about 25° from mid-northern latitudes; the finest views through a telescope come within two hours of this peak.
Features on Mars appear best when they lie near the center of its disk. For observers in North America, Aurorae Sinus stands front and center on August’s first few evenings; Sinus Meridiani takes center stage on the 9th and 10th; Syrtis Major and Hellas follow suit from the 16th to the 18th; and Mare Sirenum takes over on the 30th and 31st.
Neptune rises by 10 p.m. local daylight time August 1 and during twilight by month’s close. But the best views will come after midnight. You’ll need binoculars or a telescope to track down the planet, which glows at magnitude 7.8 in eastern Aquarius. Use 4th-magnitude Phi (ϕ) Aquarii as a guide. Neptune lies 1.4° west-southwest of this star on the 1st and drifts 0.7° farther away by month’s end. A telescope reveals the planet’s blue-gray disk, which measures 2.4" across.
Uranus trails three hours behind Neptune. The closer planet won’t tax your observing skills as much because it shines at magnitude 5.8 — bright enough to see with the naked eye under a dark sky and an easy binocular object after it climbs high in the southeast in the hours before dawn. Uranus lies in Aries, 12° south of Hamal (Alpha Arietis). Three 6th-magnitude stars lie within 2° of the planet. Use a telescope to distinguish Uranus, which shows a 3.6"-diameter disk and a distinctive blue-green hue, from the pointlike stars.
The last week of August finds Mercury in the predawn sky. The planet reaches greatest elongation 18° west of the Sun on the 26th. But unlike August evenings, the ecliptic angles nearly straight up from the eastern horizon before dawn, and Mercury stands 8° high 45 minutes before sunrise. When viewed through a telescope, the magnitude –0.2 planet spans 7" and appears 43 percent lit.
Last August brought perhaps the most watched total solar eclipse in history. On August 11, 2018, observers in northern Canada, northern Europe, and parts of Asia can witness a partial solar eclipse. With a safe solar filter, viewers in these regions can watch the Moon pass in front of the Sun. From Beijing, the Moon covers one-third of our star’s diameter just before sunset.