How do we know?
↻ One of the pages with a moving picture
A careful sky-watcher found the rules of the orbits.
- Long ago, gravity pulled a giant, spinning cloud of gas and dust together. The middle became the Sun.
- Leftover clumps came together to make the planets, all circling the young Sun.
- The Sun’s gravity pulls on every planet, like an invisible leash.
- Each planet also keeps moving forward. Pull + forward motion = a path around the Sun: an orbit.
Johannes Kepler studied careful sky measurements. He found that orbits are stretched circles, and that planets speed up when they’re closer to the Sun.
Before him, Copernicus worked in Frombork, Poland, and said that Earth goes around the Sun. Later, the apple tree at Isaac Newton’s home in Woolsthorpe, England, is said to have got him thinking about gravity.
Put together: the Sun’s gravity holds the planets, and their forward motion keeps them from falling in.
Wow number
99.8% of all the stuff in our solar system is in the Sun. Everything else together is just 0.2%!
Myth or fact?
A year is the same length on every planet. Myth. Neptune takes about 165 Earth years to go around once!
Mercury is the fastest planet. Fact. It zips around the Sun in just 88 days.
Think about it
What would happen to a planet if the Sun’s gravity suddenly switched off? (Hint: think about the sock.)
Where in the world?
Frombork, Poland where Copernicus said that Earth goes around the Sun. The apple tree at Isaac Newton’s home in Woolsthorpe, England, is said to have got him thinking about gravity — 54.3594° N, 19.6794° E.
Where these facts come from
Every number on page 15, and who measured it
This page tells us the solar system formed from a giant spinning cloud.
Solar System: Facts — NASA, the U.S. space agency
science.nasa.gov/solar-system/solar-system-facts
We checked it on 31 October 2026
This page tells us how much of the solar system's stuff is in the Sun.
Sun: Facts — NASA, the U.S. space agency
science.nasa.gov/sun/facts
We checked it on 31 October 2026
This page explains gravity, orbits and Kepler's rules.
Orbits and Kepler’s Laws — NASA, the U.S. space agency
science.nasa.gov/solar-system/orbits-and-keplers-laws
We checked it on 31 October 2026
This page tells us Copernicus worked in Frombork, Poland.
UNESCO Portal to the Heritage of Astronomy - Show entity — A world list of famous astronomy places, made with UNESCO's help
web.astronomicalheritage.net/show-entity?identity=255&idsubentity=1
We checked it on 31 October 2026
This page tells Copernicus's story and his idea that Earth goes around the Sun.
Nicolaus Copernicus (Stanford Encyclopedia of Philosophy) — The Stanford Encyclopedia of Philosophy, written by university experts
plato.stanford.edu/entries/copernicus
We checked it on 31 October 2026
This page tells us about the apple tree at Isaac Newton's home.
Woolsthorpe Manor's history — The National Trust, which looks after Newton's old home
nationaltrust.org.uk/visit/nottinghamshire-lincolnshire/woolsthorpe-manor/history-of-woolsthorpe-manor
We checked it on 31 October 2026
This page tells us how long a year on Neptune lasts.
Neptune: Facts — NASA, the U.S. space agency
science.nasa.gov/neptune/facts
We checked it on 31 October 2026
This page tells us Mercury is the fastest planet.
Mercury: Facts — NASA, the U.S. space agency
science.nasa.gov/mercury/facts
We checked it on 31 October 2026
Has this changed?
The planets have circled the Sun for a very long time, so this answer is not going to change.
What does change is the list of what is out there. Astronomers keep finding new planets around other stars.
Words from this page
- gravity
- The pull that every object has on other objects. The Sun is so big that its pull holds all the planets.
- orbit
- The curved path a planet takes around the Sun.
Try it!
Let go of a swinging sock and watch the orbit end.
1. Outdoors, tie a rolled-up sock to a string. 2. Swing it in a slow circle over your head. Keep everyone back! 3. Let go of the string.
What happens: the sock flies off in a straight line. Your pull on the string is like the Sun’s gravity on a planet.
Go further