By far the best planet shows this month are put on by (respectively), Saturn and Jupiter as both gas giants come to opposition within 17 days of each other, each visible more-or-less all night long, rising as darkness falls, moving across the meridian soon after midnight and descending toward the west-southwest horizon at dawn.
The nearly full moon will be passing both planets, first Saturn on Aug. 20, then Jupiter the following night. Venus continues to struggle to gain altitude, remaining low in the western twilight after sunset. Mercury joins Venus during the final week of August, though it will be even lower to the horizon. Finally, Mars begins a sabbatical of sorts as it will be invisible during a more than three-month transition from the evening into the morning sky.
In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm’s length measures roughly 10 degrees. Here, we present a schedule below which provides some of the best planet viewing times as well directing you as to where to look to see them.
Mercury is in superior conjunction on Aug. 1 and will have a very poor apparition during late August, in the western sky after sunset. This is its worst showing in 2021 for north temperate latitudes. The innermost planet climbs to only 9 degrees above the horizon at sunset and is 16 degrees to the lower right of Venus at month’s end. If you really want to try for it, use big binoculars and look due west about 30 minutes after sunset.
Venus continues to set about 90 minutes after the sun all month. Although its elongation from the sun is increasing, the angle between the ecliptic and the horizon is unfavorable for northern observers. The ecliptic’s slope is shallow at sunset at the beginning of August, and shallowest in September. So, from late June through October, Venus remains at the same altitude at sunset, just 15 to 17 degrees high (for observers around 40 degrees north latitude). What does change is Venus’s azimuth (its angular position relative to the horizon) at sunset, which moves from west to west-southwest during the course of August. On the evening of Aug. 10, about 45 minutes after sunset, look about 8 degrees above the western horizon for a 2.5-day old crescent moon and 6 degrees to its left you’ll see Venus.
Mars becomes lost in the sun’s afterglow and is now out of sight until late November.
Jupiter is at opposition on Aug. 19, so it is visible whenever the sky is dark and highest around midnight. It now burns right on the border between Capricornus and Aquarius, and comes into view early in evening twilight, though it’s still rather low in the southeast. This big planet peaks at a powerful magnitude -2.9. In good telescopes its disk is readily apparent, perhaps displaying darkish belts, light zones, spots, garlands and festoons. Prominent all through the overnight hours, and hovering 5 degrees below Jupiter on Aug. 21 will be a virtually full moon.
Saturn is at opposition on Aug. 2, a yellow-white gem at magnitude +0.2. It shines low in the southeast when darkness falls, but it’s easy enough to spot — unless you are hemmed in by trees and buildings to the southeast and south. As the evening grows late it rises higher while creeping out toward the south. With the exception of Jupiter to its far left (east), it is located well away from anything of comparable brightness. Saturn’s rings and moons perform an eternal, slow motion circus act for telescopic observers. The rings are currently tilted 18 to 19 degrees from edge on, less than they have been since 2012. Look for Titan, the brightest moon, about four ring-lengths west of Saturn on Aug. 14 and 31, and east around Aug. 6 and Aug. 22. On Aug. 20, about an hour or so after sunset, look southeast to see a waxing gibbous moon, and standing 5 degrees directly above it will be Saturn.
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications in New York’s lower Hudson Valley. Follow us on Twitter @Spacedotcom and on Facebook.