Facts About Earth, Our Home Planet

What makes Earth special?

Earth is the third planet from the Sun, the largest of the four rocky planets, and the fifth largest planet overall. It's the only place in the universe known to have life, and it's the only planet with liquid water on its surface.

Earth sits at a comfortable distance from the Sun, about 150 million kilometers, where water can stay liquid. That distance defines the astronomical unit (AU), the yardstick astronomers use for the whole solar system. Earth is also the only planet whose English name doesn't come from Greek or Roman mythology; it comes from old words meaning "the ground."

Earth by the numbers

Source: NASA Planetary Fact Sheet and NASA Science.

The extra quarter day in Earth's year is why we add a leap day to the calendar every four years. Sunlight takes about 8 minutes to travel from the Sun to Earth.

What's inside Earth?

Earth is built in layers, which you can explore in the cutaway diagram above. NASA describes them like this:

1. Atmosphere: a thin blanket of air, 78 percent nitrogen, 21 percent oxygen and 1 percent other gases like argon and carbon dioxide.
2. Crust: the rocky skin we live on, about 30 kilometers thick under continents and about 5 kilometers under oceans.
3. Mantle: the thickest layer, about 2,900 kilometers of hot rock that flows very slowly. NASA compares it to caramel.
4. Outer core: liquid iron and nickel, about 2,300 kilometers thick.
5. Inner core: a solid ball of iron and nickel about 1,221 kilometers in radius, reaching about 5,400 °C.

For a deeper look, with depths, temperatures and a 3D globe you can slice open, visit our layers of the Earth explorer.

Oceans, continents and ice

Oceans cover about 71 percent of Earth's surface. NASA says they average about 3.6 kilometers deep and hold 97 percent of Earth's water. Most of Earth's volcanoes, and its longest mountain range, are underwater.

The crust is broken into giant moving tectonic plates. Over millions of years they carry the continents around, crash together to build mountains, and pull apart to open new oceans. Earth is the only planet where scientists have confirmed moving plates like this.

Ice covers the Arctic Ocean around the North Pole and the continent of Antarctica around the South Pole. Water moves between the oceans, air, ice and land in the water cycle.

Why does Earth have seasons?

Earth's axis is tilted 23.4 degrees. As Earth travels around the Sun, the tilt stays pointed the same way in space. So for part of the year the Northern Hemisphere leans toward the Sun: days are longer and sunlight hits more directly, and it's summer. Six months later it leans away, and it's winter. At the start of spring and fall, both hemispheres get about the same amount of sunlight.

Many people think seasons happen because Earth gets closer to the Sun, but that's not the reason. Earth's orbit is nearly a circle, and Earth is actually closest to the Sun in early January, during Northern Hemisphere winter.

In the 3D view, turn on "Axis and equator" to see the tilt for yourself.

Earth's magnetic shield

As the liquid metal in Earth's outer core swirls, it creates a magnetic field that surrounds the planet. This invisible shield deflects most of the solar wind, a stream of charged particles from the Sun. Particles that get trapped near the poles make the glowing auroras, the northern and southern lights.

NASA notes that Earth's magnetic field flips direction now and then, on average about every 300,000 years, though the timing is irregular.

The Moon

Earth has one moon. It is about 3,475 kilometers wide, about a quarter of Earth's width, and orbits at an average distance of about 384,400 kilometers. Scientists think it formed from debris after a Mars-sized object crashed into the young Earth.

The Moon takes about 27.3 days to orbit Earth and keeps the same face toward us. Its phases repeat about every 29.5 days; see why in moon phases for kids. The Moon also steadies Earth's wobble, which helps keep our climate stable.

How fast is Earth moving?

You can't feel it, but Earth is always on the move. It spins once a day, so a person standing on the equator travels about 40,000 kilometers around Earth's middle every 24 hours, about 1,670 kilometers per hour. At the same time, Earth races around the Sun at about 29.8 kilometers per second, more than 100,000 kilometers per hour. We don't feel any of this because everything around us, including the air, moves along with us.

Earth's place among the planets

Earth is the biggest of the four rocky planets, and it sits between Venus, which is far too hot, and Mars, which is far too cold. Scientists call the region around a star where a planet could have liquid water on its surface the habitable zone, and Earth is right in it. Compare the neighbors in the planets in order table.

Fun facts about Earth

• Earth is the densest planet in the solar system.
• Earth is not a perfect ball: it bulges at the equator because it spins.
• The highest point, Mount Everest, is about 8.8 kilometers above sea level.
• Earth's atmosphere burns up most small meteoroids before they reach the ground; we see them as shooting stars.
• Earth is the largest planet that has a solid rocky surface.

Learning about Earth at home

Shine a flashlight on a tilted ball (a globe works best) and walk it around a lamp to model the seasons. Then take the facts quiz above and print the labeled Earth diagram.

To see Earth among its neighbors, compare it with Venus and Mars, or open the planets in order explorer.