NASA's Night Sky Network

December’s Night Sky Notes: Spot the King of Planets

By Dave Prosper Updated by Kat Troche

Jupiter is our solar system’s undisputed king of the planets! Jupiter is bright and easy to spot from our vantage point on Earth, helped by itsmassive size and banded, reflective cloud tops. Jupiter even possessesmoons the size of planets: Ganymede, its largest, is bigger than the planet Mercury. What’smore, you can easily observe Jupiter and its moons with amodest instrument, just like Galileo did over 400 years ago.

NASA’s Junomission captured this look at the southern hemisphere of Jupiter on Feb. 17, 2020, during one of the spacecraft’s close approaches to the giant planet. This high-resolution view is a composite of four images captured by the JunoCamimager and assembled by citizen scientist Kevin M. Gill.
Credit: NASA, JPL-Caltech, SwRI, MSSS | Image processing by Kevin M. Gill, © CC BY

Jupiter’s position as our solar system’s largest planet is truly earned; you could fit 11 Earths along Jupiter’s diameter, and in case you were looking to fill up Jupiter with some Earth-size marbles, you would need over 1300 Earths to fill it up – and that would still not be quite enough! However, despite its formidable size, Jupiter’s true rule over the outer solar systemcomes fromits enormousmass. If you took all of the planets in our solar systemand put themtogether, they would still only be half as

Look for Jupiter near the Eye of the Bull, Aldebaran, in the Taurus constellation on the evening of December 15, 2024. Binocularsmay help you spot Jupiter’smoons as small bright star-like objects on either side of the planet. A small telescope will show themeasily, along with Jupiter’s famed cloud bands. Howmany can you count?
Credit: Stellarium Web

Jupiter is easy to observe at night with our unaided eyes, as well-documented by the ancient astronomers who carefully recorded its slow movements fromnight to night. It can be one of the brightest objects in our nighttime skies, bested only by theMoon, Venus, and occasionally Mars, when the red planet is at opposition. That’s impressive for a planet that, at its closest to Earth, is still over 365millionmiles (587 million km) away. It’s even more impressive that the giant world remains very bright to Earthbound observers at its furthest distance: 600millionmiles (968millionkm)!While the King of Planets has a coterie of 95 known moons, only the four large moons that Galileo originally observed in 1610 – Io, Europa, Ganymede, and Calisto – can be easily observed by Earth-based observers with very modest equipment. These are called, appropriately enough, the Galilean moons.Most telescopes will show the moons as faint star-like objects neatly lined up close to bright Jupiter. Most binoculars will show at least one or twomoons orbiting the planet. Small telescopes will show all four of the Galilean moons if they are all visible, but sometimes they can pass behind or in front of Jupiter or even each other. Telescopes will also show details like Jupiter’s cloud bands and, if powerful enough, large storms like its famous Great Red Spot, and the shadows of the Galilean moons passing between the Sun and Jupiter. Sketching the positions of Jupiter’smoons during the course of an evening – and night to night – can be a rewarding project! You can download an activity guide fromthe Astronomical Society of the Pacific at bit.ly/drawjupitermoons

Now in its eighth year, NASA’s Juno mission is one of just nine spacecraft to have visited this impressive world. Juno entered Jupiter’s orbit in 2016 to begin its initialmission to study this giant world’s mysterious interior. The years have proven Juno’smission a success, with data fromthe probe revolutionizing our understanding of this gassy world’s guts. Juno’s mission has since been extended to include the study of its large moons, and since 2021 the plucky probe, increasingly battered by Jupiter’s powerful radiation belts, has made close flybys of the icymoons Ganymede and Europa, along with volcanic Io.What else will we potentially learn in 2030 with the Europa Clippermission?

Find the latest discoveries fromJuno and NASA’smissions to Jupiter at science.nasa.gov/jupiter/

Originally posted by Dave Prosper: February 2023. Last Updated by Kat Troche: November 2024