Jupiter and Saturn are the planets to watch as darkness falls in August 2020. They are near one another on the sky’s dome, with Saturn following Jupiter westward across the sky from dusk/nightfall until the wee hours of the morning. Last month, July 2020, was a banner month for these gas giant worlds, as Jupiter and Saturn both came to opposition in July.
Earth – in its yearly orbit – swung between these outer worlds and the sun in July 2020. Thus we were closest to Jupiter and Saturn for the year in July. Jupiter and Saturn, in turn, shone at their brightest best and were out all night long.
In some respects, though, August gives us a better month than July for viewing Jupiter and Saturn in the evening sky. That’s because these two worlds remain bright and beautiful throughout August, yet appear higher up in the sky at nightfall. That’s good news for those whose eastern horizon is obstructed, such as by trees and/or mountains.
That’s also good news for people with telescopes who don’t want to stay up until late night. Typically, the view of Jupiter’s four major moons and Saturn’s glorious rings through the telescope is sharper when these worlds are higher up in the sky. The thickness of the Earth’s atmosphere near the horizon tends to blur the spectacle.
Look first for brilliant Jupiter; Saturn is the bright object immediately to Jupiter’s east. Although Saturn is easily as bright as a 1st-magnitude star – as bright as the brightest stars in our sky – the ringed planet can’t compete with the the king planet Jupiter, which outshines Saturn by some 15 times. After all, Jupiter ranks as the fourth brightest celestial object, after the sun, the moon and the planet Venus, respectively.
Around the world, Jupiter and nearby Saturn still lurk rather low in the southeast sky in early August, and transit (reach their highest point for the night) at late evening. By the month’s end, these two worlds will transit at early-to-mid evening.
For the first time since the year 2000, look for Jupiter and Saturn to showcase their great conjunction in 2020, the closest Jupiter-Saturn conjunction since the year 1623. Astronomers use the word conjunction to describe meetings of planets and other objects on our sky’s dome. They use the term great conjunction to describe a meeting of the king planet Jupiter and golden Saturn. The last great Jupiter-Saturn conjunction was May 28, 2000. The next one will be December 21, 2020. But August 2020 presents a fine time to start watching these worlds.
Mars is the only bright evening planet (Mars, Jupiter and Saturn) not to pop out first thing at dusk/nightfall. In early August, look for Mars to be up by mid-to-late evening; and by the month’s end, Mars rises by early-to-mid evening. Thus Mars is coming up earlier daily, heading for its own opposition on October 13, 2020. At that wondrous time, Mars will actually supplant Jupiter as the sky’s fourth-brightest celestial body, after the sun, moon, and the planet Venus. That will be something to see!
In August 2020, you’ll find Mars heading toward that dramatic brightening. This month, Mars is respectably bright, more brilliant even than a 1st-magnitude star, or one of the sky’s brightest stars. Earth is now rushing along in its smaller, faster orbit, gaining on Mars, the fourth planet outward from the sun. Throughout the next three months, watch for Mars to brighten dramatically as Earth closes in on Mars, passing between it and the sun in October 2020.
At mid-northern latitudes, Mars rises roughly 10 p.m. (11 p.m. daylight saving time) in early August. By the month’s end, Mars will be up around 9 p.m. (10 p.m. daylight saving time).
At temperate latitudes in the Southern Hemisphere, Mars comes up at or near 11 p.m in early August, and about an hour earlier by the month’s end.
Let the waning moon help guide your eye to Mars on the mornings of August 7, 8 and 9, 2020.
Venus – the brightest planet – flew between the Earth and sun (at inferior conjunction) on June 3, 2020. Some 10 weeks later, Venus will reach its greatest elongation from the sun in the morning sky on August 12 or 13 (depending upon your time zone).
At mid-northern latitudes, Venus rises about 3 1/2 hours before the sun all month long.
At and near the equator, Venus rises over 3 hours before the sun in early August, decreasing slightly to 3 hours near the month’s end.
At temperate latitudes in the Southern Hemisphere, Venus rises over 3 hours before the sun in early August, decreasing to over 2 1/2 hours by the month’s end.
Throughout August, Venus in its faster orbit around the sun will be going farther and farther away from Earth. As viewed through the telescope, Venus’ waxing crescent phase will widen, yet its overall disk size will shrink. Venus’ disk is 43% illuminated in early August, and about 59% illuminated by the month’s end; Venus’ angular diameter, on the other hand, will shrink to 70% of its initial size by the month’s end.
Watch for the waning crescent moon to shine in the vicinity of Venus for several days, centered on or near August 15.
Mercury transitions out the morning sky and into the evening sky this month, so the innermost planet of the solar system is pretty much lost in the sun’s glare throughout August 2020. From northerly latitudes, you might catch Mercury before sunrise in early August; or from southerly latitudes, you might catch Mercury shortly after sunset in late August. September 2020 will feature a particularly fine evening apparition of Mercury in the Southern Hemisphere.
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: August 2020 presents 4 of the 5 bright solar system planets. Catch Jupiter and Saturn at nightfall and throughout most of the night, Mars between late evening and dawn, Venus in the predawn/dawn sky. Mercury shifts over from the morning to evening sky, and is pretty much lost in the solar glare.
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.