Earth
What is Earth?
Planets· Diameter 12,742 km. The only planet known to host life. Oceans cover 71% of its surface, and the large Moon steadies the tilt of its axis, keeping the seasons stable over long spans of time.
Orbit and size
| Diameter | 12,742 km |
|---|---|
| Distance | 1 AU (150M km) |
| Year | 365.25 d |
| Moons | 1 — the Moon |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Moons of Earth
Related events
- Comet Hyakutake sweeps past Earth
- JUICE swings past Earth again
- Voyager 1 passes one light-day from Earth(planned)
- Europa Clipper Earth flyby(planned)
- Artemis III — docking test in Earth orbit (landing moves to IV)(planned)
Earth in the skies of the Moon and Mars
From the Moon, Earth looks about four times wider than the full Moon looks to us. Because the Moon always keeps the same face toward Earth, someone standing on the near side would see Earth stay in nearly the same spot in the sky, never rising or setting. Apollo 8's famous 1968 photo 'Earthrise' was possible only because the spacecraft was orbiting the Moon.
Earth also shows phases from the Moon, but in the opposite order. On a night when we see a thin crescent Moon, Earth looks almost full from the Moon. The sunlit sides face in opposite directions. On the other hand, when we see a full Moon, Earth seen from the Moon is a nearly dark disk.
From farther away, on Mars, Earth becomes a bright star in the evening sky. In 2014 the Curiosity rover photographed Earth above the Martian horizon. In 1990 Voyager 1, about six billion kilometres away, captured Earth as a single tiny dot. Following Mars in the orbit view with Earth also shown reveals where Earth appears in the Martian sky.
The planet in depth
Earth is the only planet known to have kept liquid water on its surface for a very long time. Several conditions work together. It sits at the right distance from the Sun, so its oceans neither boil away nor freeze solid, and its magnetic field turns aside the stream of particles blowing from the Sun. Thanks to this combination, life has continued without a break for nearly four billion years.
Earth may not have started with much water. It formed close to the Sun, in a warm zone where water easily escapes. So scientists think asteroids or comets delivered water later on. Which of the two brought most of it is still being debated.
Earth's day is getting very slightly longer. The tides raised by the Moon rub against the sea floor, and this friction acts like a brake on Earth's spin. The change is tiny, about 2 milliseconds (two thousandths of a second) per century, but it adds up over time. When dinosaurs lived, a day lasted about 23 and a half hours. As Earth slows, the Moon moves 3.8 cm farther away each year.
Earth is not a perfect ball. Its fast spin makes the equator bulge a little, so the diameter across the equator is 43 km greater than the one from pole to pole. Deep inside, moving liquid iron creates the magnetic field. Every few hundred thousand years the field has flipped north and south, and the most recent flip happened about 780,000 years ago.
Frequently asked
- How big is Earth?
- The diameter of Earth is 12,742 km.
- How far is Earth from Earth?
- The distance of Earth is 1 AU (150M km).
- What are the main moons of Earth?
- The main moons of Earth are Moon.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.