Now is the time to catch Jupiter at its best.
The King of the Planets rules the winter night skies. Early December gives sky watchers a good reason to brave the cold, as Jupiter shines at its best. Look for the regal planet rising in the east at sunset, while the Sun sets to the west.
Why Opposition?
For an outer planet, we call this point ‘opposition’ as the planet sits ‘opposite’ to the Sun from our Earthly perspective. This also means that Jupiter is above the horizon for the entire evening: low to the east at sunset, high to the south at local midnight, and setting to the west at sunset.
Opposition for Jupiter in 2024 occurs on Saturday, December 7th. Jupiter is closest to the Earth (611 million kilometers distant) a day prior on December 6th. The discontinuity exists because Jupiter is currently moving away from us, while we’re headed towards the Sun.
Jupiter reached perihelion early last year on January 20-21st, 2023, while Earth heads towards perihelion about a month from now on January 4, 2025. On an 11.9 year orbit, we won’t have another perihelion-opposition year for Jupiter until 2034.
To the naked eye, Jupiter shines as a -2.8 magnitude ‘star’, in the constellation Taurus the Bull. This position, along with an opposition just two weeks prior to the December southward solstice on the 21st assures that Jupiter dominates the scene for northern hemisphere observers in 2024, riding high in the nighttime sky.
Seeing Double
Zooming in on Jupiter with a telescope even at low power gives you a view similar to Galileo’s just over four centuries ago. The four major moons of Io, Europa, Ganymede and Callisto easily pop out, even in a low power binocular view. At opposition, the moons and even Jupiter itself cast shadows nearly straight back, slowly changing angle towards quadrature. While triple shadow moon transits are rare (the next one isn’t until March 20th, 2032) double shadow transits happen in seasonal cycles a few times a year. The next one involving Io and Ganymede starts on December 23rd.
Jupiter’s fast 10 hour rotation also means that you can witness one full rotation of the gas giant in one night. This means you can spot the Great Red Spot on any given evening if you wait long enough, though to my eye, it looks more like the ‘Pale Salmon Spot’ in recent years. The major northern and southern equatorial belts are also easily apparent at low power, though the Southern Equatorial Belt has been known to pull a vanishing act roughly once a decade or so… it last did so on 2010-2011, so you could say we’re due.
Jupiter is so bright that it can cast a slight shadow, something that’s worth watching for on the freshly fallen snow. The Moon also reaches Full for December on the 15th, and passes five degrees north of the planet on the 14th, offering a chance to see Jupiter in the daytime, just before sunset.
A Teaser for Jupiter in 2025
There’s also more Jovian action in store. In the coming years, Callisto (the only major moon that can ‘miss’ Jove) resumes transits in 2026. This leads the way into the next bi-decadal mutual-eclipse season for the moons.
Don’t miss Jupiter at opposition for 2024… it’s worth braving the cold for.