The Brightest Planets in August's Night Sky: How to See them (and When)
By Joe Rao, Space.com Skywatching Columnist |
Four bright planets span the evening sky at dusk. Over in the west-southwest is dazzling Venus, which sets after the end of evening twilight. Higher up in the west-southwest stands Jupiter, while in the south-southeast is Saturn. Finally, low in the southeast is Mars which spends August slowly diminishing in splendor from its pinnacle of brilliance that it reached at the end of July. It will appear only half as bright at the end of the month, compared to the beginning of the month. During the final week of August, after Mars has set, Mercury appears low above the east-northeast horizon at the break of dawn.
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 – rushes between Earth and sun (passing inferior conjunction) and later in the month it emerges into the dawn twilight. It should be visible without optical aid by the 22nd. On August 26th, it reaches greatest elongation, 18-degrees west of the sun. This is a rather good morning apparition, because the line from planet to sun forms a steep angle with our August morning horizon. It rises 1½ hours before sunrise.
Venus – continues to outshine August's other evening planets by a huge margin, brightening from magnitude -4.3 to -4.6 over the course of the month. It reaches its greatest elongation from the sun (46-degrees) on August 17th and resembles a roughly half moon phase (49-percent illuminated) through a telescope. Three days earlier, on the evening of the 14th, a four-day old crescent moon is poised high above Venus after sunset.
Mars – dominates the sky east of Saturn. Fresh from last month's opposition and close approach to Earth, is still very bright and fiery. But it fades noticeably during August, from magnitude -2.8 to -2.1, while its disk in a telescope it shrinks in apparent size by about 15-percent. Earth is fleeing ahead of Mars around the sun and is now leaving the red planet behind. The planet is highest when due south, which corresponds to around 12:30 a.m. at the beginning of the month; two hours earlier at the end. An even wider gibbous moon can be found on the 22nd sailing far above Mars.
Jupiter – hangs modestly high in the southwest at dusk. On August 6th, the king of the planets blazes at magnitude -2.1. This is also the day Jupiter reaches east quadrature (90-percent east of the sun). For many weeks around then, the eastern edge of its disk is noticeably shadowed, and eclipses of its largest moons are more readily observable. Jupiter sets as early as 10:20 p.m. (daylight saving time) by the end of the month. On the evening of the 17th, take note of Jupiter situated a good distance to the lower right of the moon. It is also passing only 0.6° north of Zubenelgenubi, Alpha (α) Librae. This is Jupiter's third rendezvous with this 3rd magnitude double star in less than eight months, and the closest in this unusual triple conjunction series.
Saturn – can be easily located by going out in late twilight and looking south-southeast at the beginning of August, or due south around month's end. Saturn is the bright "star" roughly a third of the way up in the sky; the farther south you are the higher it will be. Later in the evening Saturn swings low to the southwest. Below Saturn is the Teapot in Sagittarius. The pot starts August upright during twilight, then gradually tilts as if pouring in the following hours and weeks. As darkness falls on the evening of the 20th, look for Saturn well to the lower left of a 75-percent illuminated gibbous moon.
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, and he is also an on-camera meteorologist for Verizon FiOS1 News in New York's Lower Hudson Valley