You can see the moon and the largest planet in our solar system from just 45 minutes after sunset on Saturday, August 21.
If your skies are clear, the moon will pass close to Jupiter. The eye-catching celestial duo, approximately one-quarter of the way up from the southeast horizontal to the point directly above (known as the zenith), will be visible by 10:30 p.m. local time. The official turning of full moon is less than 12 hours away. It will be located to the lower right, approximately 5 degrees from Jupiter.
This is about ten times larger than the moon's apparent size. That means that you should be able fit at least 10 full Moons between them in Saturday night's evening sky. They will appear closer to each other when they are visible in the sky. This is because the moon appears twice as large to our eyes than its half-degree size. It's an amazing illusion!
Related: Jupiter this week is its brightest and biggest
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This sky map shows New York City's view of Saturn, Jupiter, and the moon on Saturday (Aug. 21 at 10 p.m. EST). SkySafari app image credit
Ask your friends to point out this "dynamic duo" to you on Saturday night and to ask them how many moons they think would fit between Jupiter and the Moon. Most likely, they will answer "Four...maybe five." Then, watch their stunned expressions when you tell them that the answer is closer than 10.
A false sense of perspective
Remember that Saturday's view is a matter of perspective. Jupiter is 373,000,000 miles (600,000,000 kilometers) from Earth. The moon is only 233,000 feet (3755,000 km) away. The moon seems to be moving faster against the background of stars than the giant planet.
They will appear in the sky as eye-catching sights from Earth on Saturday night.
Because of this faster movement, Saturday night will see the moon shift its position relative to Jupiter. Jupiter will be visible to the left of the moon shortly after sunset. Jupiter will appear almost directly above the moon at 1 a.m. local. Jupiter will shift to the upper right position of the moon by Sunday morning at 5 a.m. local time, just as the two are getting ready to call it night low in the west/southwest sky.
On Sunday, August 22, the full moon passes beneath Jupiter. (Image credit: NASA/JPL-Caltech)
You can view a red spot and four additional moons
Use your telescope or high-power binoculars to see Jupiter. It is a great attraction that can be seen between 11 p.m. - 2 a.m., when it is high up in the sky, and its image is relatively calm.
Jupiter was in opposition to the sun on Aug. 19-20. This meant that it was at its largest and most brilliant year. You can see Jupiter throughout the month from dawn to dusk. You can see dark belts, light bands, and other features (sometimes called "garlands" or "festoons".
Jupiter's Great Red Spot, a famous feature of Jupiter, has changed from an oval shape to a circular one over the past 30 years. It also displays a rich orange-red coloration. At around 11 p.m. ET on Saturday (or at 3300 GMT on Sunday, August 22 GMT), it will be almost dead-center on Jupiter’s disk.
Sunday, August 22nd, observers in Eastern Europe, Eastern Africa and Asia with telescopes can simultaneously observe the small black shadows from two of Jupiter’s moons crossing the planet's disc. At 8:42 PM CEST (1842 GMT), Ganymede will be joined by Europa's shadow. These two shadows will be visible together for approximately two hours, until Europa's shadow leaves at 10:40 CEST (2040 GMT), leaving Ganymede to transit at 12:20 CEST (2220 GMT). The double shadow event in eastern Asia will be visible during the early hours of Monday morning. Image credit: Starry Night
Jupiter's bright Galilean moons, which are all always in action, are also a great help. Although they look like tiny stars, two of them are larger than our moon. You can actually see them changing their positions relative each other from one hour to the next and night to night.
If you have a small telescope, or steady-held binoculars, and you are looking at Jupiter on Saturday evening, all four of the big satellites will be visible. The moons Callisto, Io, and Europa will be visible on one side of Jupiter. On the other side, you can see the largest of the four (Ganymede), and the smallest (Europa), in a tight conjunction. At around 11:30 p.m. GMT (0330 GMT), the two moons Callisto and Io will be closest to each other. Europa will pass less than 3 arcseconds above Ganymede, so close that low-power telescopes and binoculars will most likely see them as one object. Both should be visible with smaller instruments for a few hours before and after the time.
If clouds obscure your view of Jupiter or the moon, there's another chance to see them again near one another on Sept. 17-18.
Editor's note: If you snap an amazing photo of the Jupiter and the moon in August 2021 and would like to share it for a story or photo gallery, send images and comments to spacephotos@space.com!
Joe Rao is an instructor at the Hayden Planetarium in New York. He is a writer on astronomy for Natural History magazine and the Farmers' Almanac, among other publications. Follow us on Facebook and Twitter @Spacedotcom
