The Moon
Natural satellite
The Moon is Earth’s only natural satellite. Scientists think it formed about 4.5 billion years ago when a Mars-sized world crashed into the young Earth and the debris clumped together. Its gravity creates the ocean tides.
- 3,474 kmYou could line up 4 of them across Earth.
- 27.3 daysOrbit
- 1/6 of EarthGravity
Take a closer look
Seas without water
The dark patches that make the “face” in the Moon are called maria, Latin for “seas”. Early astronomers thought they might be oceans, but they are huge plains of hardened lava that flooded giant craters billions of years ago. The bright parts are older, rugged highlands packed with craters.
Footprints that stay
The Moon has no wind or rain to wipe things away, so the astronauts’ footprints are probably still there. Moon dust is not soft like sand – it is made of tiny sharp, jagged grains that cling to everything. Apollo astronauts found it scratched their visors and smelled like spent gunpowder.
A day two weeks long
On the Moon, the Sun stays up for about two weeks, followed by two weeks of night. With no air to spread light or hold heat, the sky is black even at noon. The ground swings from hotter than boiling water in sunlight to about −130 °C in the dark.
Size it up
You could line up 4 of them across Earth. Both are drawn to the same scale.
How we found out
- 1609
Galileo points a telescope at the Moon and sees mountains and craters – it is a world, not a perfect sphere.
- 1959
The Soviet probe Luna 3 takes the first pictures of the Moon’s far side.
- 1969
Apollo 11: Neil Armstrong and Buzz Aldrin become the first humans to walk on the Moon.
- 2019
China’s Chang’e 4 makes the first soft landing on the far side.
- 2023
India’s Chandrayaan-3 lands near the Moon’s south pole, a first for any country.
Why do we always see the same face of the Moon?
The Moon spins exactly once for every trip around Earth (it is “tidally locked”), so the same side always faces us.
See it yourself
Easy with your eyes. With binoculars, look along the line between light and dark – the craters cast long shadows there.
From the encyclopedia
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