Astronomy Essentials

How to see and enjoy Jupiter’s moons

A large, dark, round shadow above a slice of Jupiter's cloudtops.
The shadow of Io, one of Jupiter’s moons, is cast on the giant planet’s cloud tops. This image was captured by the JunoCam camera aboard NASA’s Juno spacecraft, currently orbiting Jupiter. Image was acquired on September 19, 2019. Kevin M. Gill, a software engineer at NASA’s Jet Propulsion Laboratory, created this mosaic. Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ Kevin M. Gill/ CC-BY.

How to see Jupiter’s moons

All you need is a good pair of binoculars (or a telescope) to see the four largest moons of the biggest planet in our solar system, Jupiter.

Three of the four moons are bigger than Earth’s moon. And one – Ganymede – is the largest moon in the solar system. These four satellites are collectively called the Galilean moons to honor the Italian astronomer Galileo, who discovered them in 1610. September 2022 is a great month to look for Jupiter’s four large moons. That’s because the king of planets is nearing opposition – when Earth will sweep between it and the sun – on September 26. So the distance between Earth and Jupiter is now less than usual. And, on the night of opposition, Earth and Jupiter will be closer than they’ve been for 70 years.

From Earth, through a small telescope or strong binoculars, the moons of Jupiter look like tiny starlike pinpricks of light. But you’ll know they’re not stars because you’ll see them stretched out in a line that bisects the giant planet.

Depending on what sort of optical aid you use, you might glimpse just one moon or see all four. If you see fewer than four moons, that might be because a moon is behind – or in front of – Jupiter. If a moon is in front of the planet, you can sometimes see the moon’s shadow on Jupiter’s cloud-tops. That shadow is called a transit.

Going from the moon closest to Jupiter to the outermost, their order going outward from Jupiter is Io, Europa, Ganymede and Callisto.

Jupiter is easy to spot now

Chart showing very bright Jupiter, in the east in the evenings.
Here’s how to find Jupiter in September, 2022. It’s a very bright planet, brightest object in the sky after the sun, moon and planet Venus. And it’ll be ascending in the east during the evening hours this month. You can’t miss it! If you have a dark sky, look near Jupiter for the Circlet asterism in the constellation Pisces the Fish. Also watch for 4 bright stars marking the corners of a square pattern: the Great Square of Pegasus. Image via EarthSky.

What you’ll see

Writing at, Bob King has said:

Etched in my brain cells is an image of a sharp, gleaming disk striped with two dark belts and accompanied by four starlike moons through my 2.4-inch refractor in the winter of 1966. A 6-inch reflector will make you privy to nearly all of the planet’s secrets …

When magnified at 150x or higher [Jupiter’s 4 largest moons] lose their starlike appearance and show disks that range in size from 1.0″ to 1.7″ (current opposition). Europa’s the smallest and Ganymede largest.

Ganymede also casts the largest shadow on the planet’s cloud tops when it transits in front of Jupiter. Shadow transits are visible at least once a week with ‘double transits’ – two moons casting shadows simultaneously – occurring once or twice a month. Ganymede’s shadow looks like a bullet hole, while little Europa’s more resembles a pinprick. Moons also fade away and then reappear over several minutes when they enter and exit Jupiter’s shadow during eclipse. Or a moon may be occulted by the Jovian disk and hover at the planet’s edge like a pearl before fading from sight.

Images of Jupiter’s moons from the EarthSky community

Jupiter's moons: Jupiter through a telescope with two labeled dots of light, one on each side.
View at EarthSky Community Photos. | Cathy Adams in St. Stephen, New Brunswick, Canada, captured 2 of Jupiter’s moons and giant Jupiter itself on September 3, 2022. Cathy wrote: “After so many cloudy nights I was fortunate to get a beautiful clear one! And it was absolutely wonderful to enjoy a night out observing, and imaging our neighboring planets!!” Thank you, Cathy!
Jupiter: A banded planet, with 2 little dots of light (its moons) nearby.
View at EarthSky Community Photos. | Around the time of its yearly opposition, Jupiter is brightest in our sky, best through a telescope, and visible all night. Michael Terhune in Lunenburg, Massachusetts, captured Jupiter near last year’s opposition, in August of 2021. He wrote: “My sharpest image of Jupiter! Showing 2 of its Galilean satellites Io and Europa. The Great Red Spot is also visible.” Thank you, Michael.
A full Jupiter on the left and a close-up of the moon and its shadow on Jupiter's clouds on the right.
View at EarthSky Community Photos. | Sona Shahani Shukla in New Delhi, India, caught a transit of the innermost Galilean moon, Io, across the face of Jupiter on July 7, 2021, and wrote: “Io appears to be skimming Jupiter’s cloud-tops, but it’s actually 310,000 miles (500,000 km) from Jupiter. Io zips around Jupiter in 1.8 days, whereas our moon circles Earth every 28 days. The conspicuous black spot on Jupiter is Io’s shadow and is about the size of the moon itself (2,262 miles or 3,640 km across). This shadow sails across the face of Jupiter at 38,000 mph (17 km per second).” Thank you, Sona!

Special viewings of Jupiter’s moons

As with most moons and planets, the Galilean moons orbit Jupiter around its equator. We do see their orbits almost exactly edge-on, but, as with so much in astronomy, there’s a cycle for viewing the edge-on-ness of Jupiter’s moons. This particular cycle is six years long. So every six years we view Jupiter’s equator – and the moons orbiting above its equator – at the most edge-on. During these special times, we can see the moons eclipse and cast shadows on not just giant Jupiter but on each other.

In 2021 we were able to view a number of mutual events (eclipses and shadow transits) involving Jupiter’s moons. The next cycle of mutual events will be in 2027.

Another special event, a rare triple transit, occurs on October 18, 2025, when three of Jupiter’s moons will pass in front of the giant planet at once. The last time Earth could witness a triple transit was in 2021. Triple transits are not visible from all parts of the globe, however.

You can find information here for dates and times to observe the Galilean moons.

Part of Jupiter with Great Red Spot and 4 largest moons, enlarged and colorful, on black background.
Composite image of Jupiter and its 4 Galilean moons. From left to right the moons are Io, Europa, Ganymede and Callisto. The Galileo spacecraft obtained the images to make this composite in 1996. Image via NASA Photojournal.

Jupiter at opposition in September 2022

On September 26, 2022, Jupiter is at opposition, when the planet is opposite the sun in the sky as seen from Earth. When Earth passes directly between Jupiter and the sun, we’ll see Jupiter rise at sunset and set at sunrise. Opposition is the middle of the best time of the year to see a planet, since that’s when the planet is up and viewable all night and is generally closest for the year. But any time Jupiter is visible in your sky you can view Jupiter’s four major moons.

So if you get a chance, grab some binoculars or a small telescope and go see Jupiter’s Galilean moons with your own eyes!

Click here for recommended sky almanacs; they can tell you Jupiter’s rising time in your sky.

Diagram of sun, Earth, and Jupiter lined up with orbits and line of sight shown.
Opposition – when Earth is directly between Jupiter and the sun – is the best time to observe the largest planet and its 4 Galilean moons. In 2022, Jupiter’s opposition is September 26. Image via EarthSky.

Bottom line: You can see Jupiter’s moons – Io, Europa, Ganymede and Callisto, known as the Galilean satellites – with your own eyes with the help of binoculars or a small telescope.

Check here for dates and times to observe the Great Red Spot

September 6, 2022
Astronomy Essentials

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