NASA - National Aeronautics and Space Administration

The sun is a huge, glowing ball of gases at the center of the solar system. The Earth and the other eight planets travel around the sun. The sun is only one of billions of stars in the universe, but it is more important to people than any other star. Without the heat and light of the sun, there could be no life on the Earth.

Image to left: The sun is the largest object in the solar system. It is 109 times larger than the Earth. Credit: World Book illustration by Roberta Polfus

If the sun were the size of a skyscraper, the Earth would be the size of a person. The moon would be the size of a medium-size dog standing next to the person. Jupiter, the largest planet, would be the size of a small building.

The sun is the star that is closest to the Earth. Scientists study the sun to lean about stars that are much farther away. The surface of the sun is made up of hot gases that give off light and heat.

How the Sun Affects the Earth

Sunlight affects the weather of an area. The temperature of any place on the Earth depends on where the sun is in the sky. Tropical areas near the equator, an invisible line around the middle of the Earth, have a hot climate because the sun shine almost directly overhead at noon. Areas near the North Pole and the South Pole have cold weather because the sun never rises very high there.

The sun gives us heat, light, and other kinds of energy. All life on Earth -- people, animals, and plants -- depends on this energy from the sun. Plants use sunlight to make their own food. As they make their food, plants give off a gas called oxygen. People and animals eat the plants and breathe in oxygen. In turn, people and animals breathe out the gas carbon dioxide. Plants mix carbon dioxide with energy from sunlight and water from the soil to make more food.

Image to right: The surface of the sun is made up of hot gases that give off light and heat. Credit: NASA/ESA/Solar & Heliospheric Observatory

How the Sun Was Formed

Throughout space, there are huge clouds of gases and dust. New stars are made when parts of the gases and dust join together and form a tight mass. The mass starts to make heat. As the mass of gases and dust gets smaller, the center of the mass gets hotter. Finally, the center becomes so hot that the mass of gases and dust begins to shine as a star.

Scientists believe the sun was made from a mass of gases and dust. They think the planets were formed from gases and dust that collected at different distances from the center of the sun.

How to cite this article: To cite this article, World Book recommends the following format: "Sun." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.

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