Jupiter will reach opposition on September 26 or 27, depending on your timezone. This means that it is directly opposite the Sun from our vantage point, rising near sunset and setting near sunrise. This alone makes it an excellent time to observe the Solar System’s largest planet, but it will also be the closest Jupiter has been to Earth in at least 59 years, making the giant planet’s moons and cloud formations particularly visible. It’s time to break out the telescopes and binoculars, or simply gaze in awe with your own eyes. Three days later, one of the most important parts of the Juno mission to the Jupiter system will take place.
What does planet in opposition mean?
Jupiter oppositions occur roughly every 13 months because Jupiter has traveled just under one-twelfth of its path in the time it takes Earth to whizz around the Sun, much like the tortoise being outrun by Achilles. We need an extra month after returning to the same point in our orbit where opposition occurred the last time for the Earth to overtake it again.
Every opposition would occur at the same distance if the planets moved in perfect circles. Because planets orbit in ellipses, Jupiter’s closest approach to the Sun, known as perihelion, occurs every 11.9 years. Jupiter is nearly 40 million kilometers (24.9 million miles) closer to the Sun, and thus potentially to us, at perihelion than it is at its average distance.
The closer opposition is to Jupiter’s perihelion, the shorter the distance between Jupiter and Earth, though this is complicated by Earth’s own 5-million-kilometer (3.1-million-mile) variation from the Sun.
How close will Jupiter be?
Jupiter and Earth have a theoretical distance of 588 million kilometers (365 million miles). We won’t get as close this time because perihelion isn’t until January 2023, but the Earth-Jupiter distance will be within 0.5 percent of the minimum next week. It will be the closest the Earth has been to Jupiter since at least 1963 (some reports incorrectly state 1951), and it will not be repeated for centuries.
It may be difficult to tell between this opposition and the previous or previous one, both of which were also fairly close. On the other hand, if you remember how the giant planet looked in 2016, the difference should be quite significant. Furthermore, because Jupiter is currently almost exactly on the celestial equator, it appears good from all over the planet, including the poles, rather than being best in one hemisphere.
This is a good opportunity for people with good eyesight and dark skies to see if they can spot some of Jupiter’s moons without using an astronomical instrument.
On September 29, when Jupiter’s distance from Earth has changed only slightly, Juno will make its only planned flyby of Europa, just 356 kilometers above the surface – closer than the ISS orbits to Earth. It will be the closest approach to Europa since 2000, and it will not be repeated for at least a decade.
Juno’s mission will include searching for bodies of water within the icy shell, geyser plumes, and the water vapor atmosphere.