Jupiter: Everything You Wanted to Know About the King of Planets
We've got some fascinating facts about our solar system's largest planet.
Quick Reference: Jupiter
- Type: gas giant. Largest planet in the solar system.
- Diameter: 88,846 miles. 11 times Earth’s.
- Mass: 2.5 times the mass of all other planets combined.
- Day: 9 hours 56 minutes (fastest rotation of any planet).
- Year: 11.86 Earth years.
- Moons: 95 confirmed (as of 2024 NASA count).
Jupiter is the biggest, brightest, and most thoroughly studied of the outer planets. It is the second-brightest planet in our sky after Venus, its four largest moons were the first non-Earth moons ever seen by humans (Galileo, 1610), and its iconic Great Red Spot is a storm bigger than Earth that has been raging for at least 350 years. Here are the key facts about Jupiter and how to see it tonight.
The Basic Facts
Jupiter is a gas giant, meaning it has no solid surface to land on. Beneath the cloud tops, the atmosphere becomes denser and denser until it transitions to a liquid metallic hydrogen ocean, then to a small rocky core at the center.
Jupiter is 318 times more massive than Earth. It rotates faster than any other planet: a Jupiter day is just under 10 hours.
The Great Red Spot
The Great Red Spot is a massive anticyclonic storm in Jupiter’s southern hemisphere. It is at least 350 years old (first reliably recorded in 1665 by Giovanni Cassini) and currently about 10,000 miles wide, large enough to swallow Earth.
The spot has been shrinking. In the 1800s it was three times Earth’s size. The cause of the shrinkage isn’t fully understood.
The Moons
Jupiter has 95 confirmed moons. The four largest (Io, Europa, Ganymede, Callisto) are the Galilean moons, visible from Earth through binoculars or a small telescope.
Europa, with a subsurface ocean of liquid water, is one of the most promising places to look for life elsewhere in the solar system. NASA’s Europa Clipper mission launched in 2024 to study it.
How to See Jupiter Tonight
Jupiter is the brightest object in the night sky after Venus and the moon. It’s visible for about 10 months of each year, with the best viewing around opposition (when Earth is between Jupiter and the sun, roughly every 13 months).
Binoculars show Jupiter as a tiny disc with up to four small dots in a line (the Galilean moons). A 4-inch telescope shows the cloud bands and, when oriented right, the Great Red Spot.
Frequently Asked Questions
Is Jupiter visible to the naked eye?
Yes. Jupiter is the second-brightest planet after Venus and is naked-eye visible most months of the year. It looks like a bright steady (non-twinkling) ‘star’ in the eastern evening sky or western morning sky.
Could Jupiter become a star?
No. Jupiter would need to be about 80 times more massive to start fusion and become a brown dwarf or red dwarf star. As-is, it is a planet.
Why is Jupiter so important to Earth?
Jupiter’s gravity helps deflect comets and asteroids that might otherwise hit the inner solar system. Some astronomers credit Jupiter with making Earth more habitable by acting as a long-term gravitational shield.
When was Jupiter’s Great Red Spot first seen?
Giovanni Cassini’s 1665 observation is the earliest reliable record. It may have been observed by Robert Hooke a year earlier, but the records are less clear.
Jaime McLeod
Jaime McLeod is a longtime journalist who has written for a wide variety of newspapers, magazines, and websites, including MTV.com. She enjoys the outdoors, growing and eating organic food, and is interested in all aspects of natural wellness.
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- Jaime McLeod
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I always enjoy your informative posts. Lately, on a few occasions, I have gone out in the late evening and viewed what I believe is Jupiter twinkling in the sky. I understand it has been the planet closest to the moon. Makes me wish I could purchase a decent telescope.
We’ve (me and my hubby) seen the Saturn on the 27th on top of the moon,it is actually a Pretty bright star up a sky (we observed it without the telescope,or binoculars),we live in Nigeria,thanks a bunch,last year we witness a complete (full) eclipse of the moon.Thanks farmer’s almanac keep it up. What’s next?
these are good facts about Jupiter because if you have a project you can you theses notes
God is so awesome
I live inMissouri. Could someone please tell me what that very bright star is that I can see towards the west? Or tell me just what it is please.
Hi Vickie,
Short of driving to Missouri and standing right next to you, there’s no way I can know for sure which star you mean. However, you’re probably looking at the planet Venus. After the Moon, Venus is usually the brightest body in the night sky, and it is sitting to the west right now.