Earth

Our planet. The one you are standing on right now. Earth is the only planet with life — that we know of! Let's keep it safe.

🕒 When can I see it?🚀 Travel there

What it is

Our home; only known planet with life, liquid water oceans, moving tectonic plates.

Planet: Round, orbits a star, and has swept its orbit clear. Every kind of thing there is →

How to find Earth

Its position moves, so there is no fixed place on a map to point at. The Planetarium works out where it is for your own place and date.

Show me Earth in tonight's sky

Worth knowing about Earth

Earth is our reference size. In weight, our reference mass. Our home base — the measuring stick for every other planet's distance. Its year: one trip around the calendar. Earth spins all the way around in about 23 hours 56 minutes, but the Sun doesn't rise again until 24 hours have passed — those extra 4 minutes are Earth 'catching up' after moving a bit further along its orbit.

What it is made of: Rocky, moving tectonic plates, liquid water oceans, only known planet with life.
Its weather: Nitrogen-oxygen atmosphere, water cycle, all kinds of climates.
How far away it is: Earth's distance from the Sun is the ruler everything else in the solar system is measured against: we call it one astronomical unit.; How we know: For nearby planets, scientists bounce radar signals off them and time the echo (light-speed x time = distance); Kepler's laws then let scientists calculate every other planet's distance, and Newton's law of gravitation explains why. Masses are found by watching how strongly a planet's gravity tugs on a moon, another planet, or a passing spacecraft. Rung 3 of the cosmic ladder — how the solar system is arranged
What makes it worth knowing: From flat ground or the beach (eye height ~1.6 m), you can see about 5 km in one direction — 10 km total looking both ways, about 1/4,000th of the way around the whole planet. From a hill about 125 m tall (roughly a 30-story building), the horizon stretches to about 40 km — 80 km total, about 1/500th of the way around Earth. To the Moon: light takes about 1.3 seconds to get there; driving nonstop by car at 100 km/h would take about 160 days — over five months. Fun coincidence: all seven other planets could almost be lined up side-by-side in the gap between Earth and the Moon. To the Sun: light takes about 8 minutes 20 seconds; driving there nonstop by car at 100 km/h would take roughly 171 years.

How did anyone measure the Earth in the first place?

The numbers

Across	12 742 km
Distance from the Sun, on average	1 AU ~150 million km · sunlight takes 8 minutes
Once round its orbit	365.3 days
One day there	24.0 hours
Temperature	15 °C (from -89 to 57)
Made of, among other things	nitrogen, water, carbon dioxide, iron, rock (basalt), sulfur, tin, lead, methane

How anyone knows this

Nobody flew a tape measure out there. Every number on this page was worked out from the ground:

What it belongs to

☀️ Everything the Sun holds, in one place 📖 How the solar system fits together

Then go outside

Clear tonight? The Planetarium will show you what is worth a look. Then just go out.

🌙 Plan an evening outside 🌌 Everything else in the sky