Earth, Venus, and Mars are neighbors in the solar system. They’re also about the same size.
Billions of years ago, Venus and Mars may have had rivers, lakes, and even oceans. What happened? Water on Venus and Mars was lost to space, due in part to the direct impact of solar wind. Earth’s magnetic field, however, protects it from solar wind. Only Earth has the proper atmosphere and distance from our Sun to preserve water and sustain life.
Sunblockers
The different layers of Earth’s atmosphere work as a screening system to block out the Sun’s harmful radiation. Most visible light and radio waves make it to Earth. But dangerous X-rays are stopped in the ionosphere. Likewise, the ozone layer of the stratosphere absorbs most—but not all—of the Sun’s ultraviolet rays. Infrared light is blocked by water vapor in the troposphere. ▶
Sun Facts
Distance from Earth
Average of 93 million miles


Solar Attraction

The Sun ejects charged particles that travel in solar wind at 1 million miles an hour. Some of these particles come zooming toward Earth. Other particles travel to different parts of space.
Surrounding the magnetic field is the magnetosphere. It protects Earth from most of the charged particles from the Sun.
Magnetic field lines are invisible lines of force between poles.
Earth is like a huge magnet, with its magnetic field extending far into space.
Some charged particles from the Sun enter Earth’s magnetosphere. They are channeled along the magnetic field lines toward the North and South Poles.
Solar wind distorts the shape of the magnetosphere.
On the Sun side of Earth, the magnetic field lines are squashed by pressure from solar wind.
In the ionosphere, charged particles collide violently with gas atoms, causing the atoms to give off light that is visible around the poles. This light is known as the aurora borealis, or northern lights, in the Northern Hemisphere, and the aurora australis, or southern lights, in the Southern Hemisphere.
On the side of Earth away from the Sun, the magnetic field lines are stretched out.

▲ Mix sunlight and water and you get weather. For instance, the Sun causes water to evaporate and become clouds. Those clouds help reflect back into space about 34 percent of the Sun’s visible light. The Sun helps warm the atmosphere, but the heating is uneven, in part because the planet’s cloud cover is spotty. This uneven heating causes differences in air pressure that generate wind and changes in the weather.
Sunlight hits our backyards and beaches as tiny bits of energy called photons. Traveling at the speed of light, or about 186,000 miles per second, it takes a photon about eight minutes to reach Earth. The atmosphere (the thin layer of gases surrounding our planet) blocks out much of this sunlight. With no atmosphere, the sunny side of Earth would be 250 degrees F while the dark side would be minus 250 degrees! ▼


◀ We capture some of the Sun’s energy every time we eat. Plants use sunbeams to make their own food, which is stored in their leaves. This process, called photosynthesis, is the key to life on Earth. Plant-eating animals like cows and deer get their energy from plants, and are in turn eaten by humans and by other animals.
Most of the energy that powers machines comes from the Sun. For instance, oil and coal are the fossilized remains of ancient plants and animals. Burning them releases the solar energy that those creatures stored up millions of years ago. Wind, water, and other ways of generating power are also tied to the Sun. ▶
