August guide to the bright planets
Venus is the brightest planet, and – as seen from around the world – it’s dazzling this month in the west after sunset, impossible to miss as the evening “star.”
At mid-northern latitudes, Venus sets roughly 2 hours after the sun in early August. By the month’s end, that’ll taper to about 1 1/2 hours after sunset. What’s interesting is that – as seen from mid-northern latitudes – Venus reached its highest altitude after sunset in June, 2018. And yet Venus’ greatest elongation (greatest apparent distance from the setting sun) happens this month, on August 17. Why? It’s because of the angle of the ecliptic, which marks the path of the sun, moon and planets across our sky. From our northerly latitudes, the ecliptic is beginning to slant downward after sunset now, keeping Venus low in the sky.
The Southern Hemisphere has the advantage in seeing Venus right now. From there, the ecliptic is beginning to slant upward, placing Venus above the sunset (rather than to one side of it as for us northerners). Venus does indeed climb highest up in the evening sky in August as viewed from the Southern Hemisphere, just as you would expect during a greatest elongation. At temperate latitudes in the Southern Hemisphere (South Africa, southern Australia), Venus sets about 3 1/2 hours after sunset throughout the month.
Circle August 14, 15 and 16 on your calendar. That’s when the young moon will be sweeping past Venus (and Jupiter) in the evening sky. The western twilight will make the pairing all the more picturesque. See chart above.
Look for Venus to adorn the western evening sky until October 2018.
Jupiter remains bright and beautiful throughout August 2018. Its opposition took place on May 8-9, 2018, so the planet is now slowly shifting westward at each night’s sunset. In the Northern Hemisphere, you’ll find Jupiter highest up for the night around dusk or nightfall, appearing a bit west (right) of due south. In the Southern Hemisphere, you’ll see Jupiter nearly overhead at dusk.
Jupiter is brighter than any star, but it’s not brighter than Venus, which beams mightily in the west after sunset. And it’s not brighter than Mars.
Jupiter shines in front of the constellation Libra the Scales until November 2018. Look for Libra’s brightest stars near Jupiter, Zubenelgenubi and Zubeneschamali (both star names are pronounced with the same rhythm as Obi-Wan Kenobi of “Star Wars”).
If you aim binoculars at Zubenelgenubi, you’ll see this star as two stars. Zubeneschamali, meanwhile, is said to appear green in color, although, astronomers say, stars can’t look green.
Saturn and Mars adorn the eastern half of the sky at dusk and nightfall. During the first few weeks of August, Saturn transits – reaches its high point for the night – at about the same time that Venus sets (roughly 9 p.m. local time or 10 p.m. local daylight saving time). Then Mars transits some two hours after Saturn does.
Near the month’s end, Saturn will transit at roughly 8 p.m. local time (9 p.m. local daylight saving time), and throughout the month, Mars will transit about two hours after Saturn does.
Click here for a recommended sky almanac providing you with the transit times for the planets.
Middle to late evening offers a better view of Saturn and Mars, as these worlds are seen higher up in the sky than they are at nightfall.
You can tell Mars from Saturn because Mars has a reddish color and Saturn looks golden. Binoculars show their colors better than the eye alone.
Watch for the moon to pair up with Saturn on or near August 20 and with Mars on or near August 23.
At present, both Saturn and Mars shine more brilliantly than a 1st-magnitude star. However, Mars is brighter than Saturn. Saturn’s brilliance peaked at its June 27 opposition, and Mars’ brilliance came to a head at its July 27 opposition.
It’s not often that Mars outshines Jupiter, normally the fourth-brightest celestial object to light up the sky, after the sun, moon and Venus. But, for a couple of months in 2018, Mars will outshine Jupiter from about July 7 to September 7, 2018.
Both Mars and Saturn are slowly dimming throughout the month. Because Mars is dimming at a faster rate than Saturn is, Mars will be about 15 times brighter than Saturn at the beginning of the month, and some 10 times brighter by the month’s end.
Remember Mars’ historically close opposition of August 28, 2003? That year, it was closer and brighter than it had been in some 60,000 years. The July opposition was the best since 2003, and what’s more, Mars will remain bright and beautiful all through August 2018!
Mercury, the innermost planet of the solar system, moves out of the evening sky and into the morning sky on August 9, 2018. Mercury probably won’t first become visible in the morning sky until August 20th or so. The last week of August and the first several days of September will provide a good view of Mercury for the Northern Hemisphere and the southern tropics. Mercury will be harder to spot from temperate latitudes in the Southern Hemisphere.
During the last week of August at mid-northern latitudes, Mercury will rise about 1 1/2 hours before sunrise. At temperate latitudes in the Southern Hemisphere, on the other hand, Mercury only rises an hour or less before the sun. Click here for a recommended almanac telling you when the sun and Mercury rise into your sky.
Mercury will reach its greatest elongation from the sun on August 26, 2018, and its reign as the morning “star” will extend until September 21, 2018 (same date that Venus reaches its greatest illuminated extent in the evening sky).
What do we mean by bright planet? By bright planet, we mean any solar system planet that is easily visible without an optical aid and that has been watched by our ancestors since time immemorial. In their outward order from the sun, the five bright planets are Mercury, Venus, Mars, Jupiter and Saturn. These planets actually do appear bright in our sky. They are typically as bright as – or brighter than – the brightest stars. Plus, these relatively nearby worlds tend to shine with a steadier light than the distant, twinkling stars. You can spot them, and come to know them as faithful friends, if you try.
Bottom line: In August 2018, four planets arc across the sky at dusk and nightfall. Venus lights up the western sky, with Jupiter shining above Venus, whereas Mars lords over the southeast sky, with Saturn shining above Mars. Mercury becomes a morning “star” by the last week of August. Click here for recommended almanacs; they can help you know when the planets rise, transit and set in your sky.
Bruce McClure has served as lead writer for EarthSky’s popular Tonight pages since 2004. He’s a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.
Published on EarthSky