Blue Moon, Saturn, Jupiter August 19 to 22
Moon passes first Jupiter, then Saturn
As it moves in orbit around Earth, the moon travels eastward in our sky. You’ll notice the moon’s orbital motion if you watch for it near Jupiter and Saturn from August 19 to 22, 2021. The moon will sweep 4 degrees south of Saturn on August 20 at 22 UTC. It’ll be a full moon – a Blue Moon – that sweeps 4 degrees south of Jupiter on August 22 at about 05:00 UTC. The exact times won’t matter to you, as you stand outside looking for these bright worlds in space. Jupiter will be the brightest object besides the moon, ascending in the eastern half of the sky throughout the evening. Fainter Saturn will be to the west of Jupiter (more toward the sunset direction). And, if you’re watching for them at nightfall, turn around and look west. You’ll see an even brighter planet in that direction in the very early part of the night: beautiful, blazing Venus.
And here’s something wonderful. Jupiter reaches opposition on the night of August 19-20, 2021. That’s a yearly event, during which time we on Earth fly between Jupiter and the sun in our smaller, faster orbit. Our motion in orbit places Jupiter opposite the sun in our sky. The planet rises at sunset and is visible all night, a sight to behold.
Why will the full moon be near Jupiter this month? It’s because a full moon is opposite the sun. And Jupiter at opposition is opposite the sun. Voila. Jupiter will be near this month’s full moon.
Blue Moon, Saturn, Jupiter
This August full moon is a seasonal Blue Moon. It’s not the second full moon in a month. It’s the 3rd of four full moons in one season.
For the Northern Hemisphere, this weekend’s full moon counts as a summertime Blue Moon. In the Southern Hemisphere, it’s a wintertime Blue Moon. Either way, it’s the 3rd of four full moons between the June solstice and September equinox.
The moon will appear full to the eye throughout the weekend. To astronomers, however, a full moon occurs at a well-defined instant: at the moment that it’s directly opposite the sun (in ecliptic longitude). The moon turns precisely full on Sunday, August 22, at 12:02 UTC. Translate UTC to your time zone. At U.S. time zones, that converts to 8:02 a.m. EDT, 7:02 a.m. CDT, 6:02 a.m. MDT, 5:02 a.m. PDT, 4:02 a.m. Alaskan Time and 2:02 a.m. Hawaiian Time.
Bottom line: Blue Moon, Saturn, Jupiter. This upcoming weekend – August 19 to 22, 2021 – watch for these worlds in your sky.