Hello Jupiter! How to observe a gas giant

Finding Jupiter with the naked eye

When our ancient ancestors looked up at the sky, they saw a brilliant yellowish-white dot. It shone oddly steadily compared to the twinkling stars, and found refuge in a different constellation every year. Named ‘Jupiter’ by the Romans, what we now know to be a planet can be spotted by modern-day humans from our own gardens. All you need is a clear night sky, your eyes and, if you would like more detail, binoculars or a telescope.

Jupiter is one of the brightest objects in the night sky. It is visible throughout the year, becoming difficult to spot only during short periods of time when it is too close to the Sun from our perspective on Earth.

For sky watchers in the northern hemisphere, Jupiter rises in the east, sets in the west and can be seen in the south at the midpoint of its journey across the sky. Use a free stargazing application to check where Jupiter is in relation to other objects such as the Moon. You can even try taking a picture of Jupiter with your phone camera; shown here is an example of a photo you can capture without any photography skills!

Viewing Jupiter through binoculars or a telescope

Some 400 years ago, Galileo was the first person to view Jupiter through a rudimentary telescope, which would have had a similar power to modern binoculars. Dig out your binoculars to see Jupiter as Galileo did.

During his observations, Galileo saw what looked like four faint stars close to Jupiter – he soon realised that these were actually Jupiter’s very own moons! Like the Italian astronomer, you will likely also spot up to four ‘Galilean’ moons: Io, Europa, Ganymede and Callisto. These orbit quickly, so over the course of several evenings you will see them weave back and forth around the gas giant.

Observing this motion is what inspired Galileo to realise that these objects were moons rather than stars and provided evidence that most celestial objects did not revolve around Earth. But that’s not all: decades later, Danish astronomer Ole Rømer timed the eclipses of Io by Jupiter to demonstrate that – contrary to dominant opinion at the time – light does not travel instantaneously, and even provided a first estimate of the speed at which light travels.

Telescopes have come a long way since Galileo’s homemade version, but when observing Jupiter, using even a basic telescope will reveal a lot of extra detail. It is best to start out at the lowest magnification setting yours offers and work up from there.

Jupiter itself is so bright that the Galilean moons become invisible as they pass in front of the planet, but using a telescope may allow you to see their shadows on Jupiter’s surface.

Top tips for a good observing experience

• Go outside on a cloudless night – make the most of winter, when nights are longer
• Look for one of the brightest points of light in the night sky, shining steadily amongst the twinkling stars
• Use a stargazing app to help you find where Jupiter is in the sky
• Give binoculars or a telescope 20–30 minutes to cool down outside, bringing them into equilibrium with the ambient temperature for an even better view
• To take a steady photo, place your camera directly against your telescope’s eyepiece and use tape to attach a smartphone or a tripod for a camera.
• For more advanced amateur astrophotography, stack multiple images/video frames to avoid atmospheric effects and increase the signal intensity (see image below)
• Use coloured filters to enhance certain features of the planet – green and dark blue are particularly useful for enhancing the red belts and spots

Hello Juice!

ESA’s Juice mission launched on 14 April 2023 as humankind’s next Jupiter explorer, taking a closer look at the giant planet and its ocean-bearing Galilean moons to uncover their mysteries. Juice will push beyond the discoveries made so far, which arguably raised more questions than they answered.

Juice aims to shed light on enigmas such as: What are Jupiter’s ocean worlds like? Could life exist, or ever have existed, in the Jupiter system? How can we compare Jupiter to alien worlds we find orbiting other stars?

By getting up close to Jupiter and its largest Galilean moons, Juice will reveal more than we on Earth can even imagine about the striped beauty that graces our night skies. So, in addition to saying “hello Jupiter” when you look up at the night sky, you can say “hello Juice” as well.

Happy planet hunting!