Jupiter the magnificent
The huge planet Jupiter is closest to the Earth and the brightest it has been for 70 years. This is the chance of a lifetime to see this giant of the solar system at its best.
Jupiter rises at sunset and sets at sunrise this month. Look up to the East after dark. You really can’t miss it.
Jupiter takes 12 years to orbit the Sun. Since the Earth only takes a year, we catch up with Jupiter and pass between it and the Sun every 13 months.
When this happens, we call it an “opposition” because Jupiter and the Sun are opposite each other in the sky. Jupiter’s orbit is also “eccentric ”– that is, not quite circular – and it will be at its closest to the Sun in January 2023. That is why it is so close and bright right now.
Jupiter is more than 10 times the diameter of the Earth, and has more mass than all the other planets in our solar system combined. It is entirely gas and fluid (mostly hydrogen and helium) throughout with no solid surface.
Our eyes see visible light. The brilliance of Jupiter that you can see comes from reflected sunlight.
But Jupiter shines even more brightly in infrared light that we cannot see. It radiates 400 quadrillion Watts of its own energy.
That is 8-billion times more energy than Eskom could produce if all its power plants actually worked.
Jupiter creates that energy from its gravity by shrinking by a mere 1mm per year. This is similar, but on a much grander scale, to the energy released when you drop a glass on the floor and it shatters from the gravitational energy released.
The James Webb Space Telescope observes infrared light. This is light that is too long in wavelength to see with our eyes. But Webb was designed so it can see infrared and it has recently taken the spectacular picture of Jupiter that you can see here.
All that energy Jupiter makes by shrinking has heated its core to 24,000°C, driving tremendous weather at the surface. The bands in the picture are caused by winds blowing at 400km/h.
The Great Red Spot (which looks white in this infrared picture) is a hurricane bigger than the Earth, which has been blowing at 600km/h for centuries. The other tiny bright spots you can see are the tops of giant thunderstorms 50km high.
Then look at the north and south poles. Coloured red in this picture, those are gigantic aurorae far bigger than the Earth. We astronomers have found more than 5,000 planets orbiting other stars and some of those planets have two suns.
We call those planets “Tatooines” after the fictional home planet of Luke Skywalker in Star Wars. In the first film in that series there is a scene of Luke watching a double sunset.
When the solar system formed 4.6 billion years ago, the Sun spun off a disk from which the planets formed. Jupiter now has only a thousandth the mass of the Sun. But if it had been 80 thousandths the mass of the Sun, its core would have heated enough from the gravity to ignite hydrogen fusion – the power of the stars – and Jupiter would have been a faint red dwarf star. That second star in the solar system would have been a ten thousandth as bright as the Sun, so it would have been spectacular to see, but would not have heated the Earth significantly. We would then have had two suns. We, too, could have been a Tatooine. Imagine that.
— Donald Kurtz, Extraordinary Professor at North-West University in Mahikeng, has an A-1 rating from the South African National Research Foundation. He is also Emeritus Professor at the University of Central Lancashire and Visiting Professor of Astrophysics at the University of Lincoln and was Professor of Astronomy at the University of Cape Town. Don has over 500 professional publications and was awarded the 2022 Service Award of the Royal Astronomical Society for a lifetime of public outreach and for his service on many international committees. He and his wife live in Port Alfred.