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Solar System

Sun

closest star, eastern horizon, human eyes, temperature of Earth, average star

Deeper web pages:

>  Physical Characteristics

>  The Sun as a Star

>  The Sun's Energy

>  Inside the Sun

>  The Sun's Atmosphere

>  History of Studying the Sun

Sun, closest star to Earth. The Sun is a huge mass of hot, glowing gas. The strong gravitational pull of the Sun holds Earth and the other planets in the solar system in orbit. The Sunís light and heat influence all of the objects in the solar system and allow life to exist on Earth.

The Sun is an average staróits size, age, and temperature fall in about the middle of the ranges of these properties for all stars. Astronomers believe that the Sun is about 4.6 billion years old and will keep shining for about another 7 billion years.

For humans, the Sun is beautiful and useful, but also powerful and dangerous. As Earth turns, the Sun rises over the eastern horizon in the morning, passes across the sky during the day, and sets in the west in the evening. This movement of the Sun across the sky marks the passage of time during the day. The Sunís movement can produce spectacular sunrises and sunsets under the right atmospheric conditions. At night, reflected sunlight makes the Moon and planets bright in the night sky.

The Sun provides Earth with vast amounts of energy every day. The oceans and seas store this energy and help keep the temperature of Earth at a level that allows a wide variety of life to exist. Plants use the Sunís energy to make food, and plants provide food for other organisms. The Sunís energy also creates wind in Earthís atmosphere. This wind can be harnessed and used to produce power.

While it lights our day and provides energy for life, sunlight can also be harmful to people. Human skin is sensitive to ultraviolet light emitted from the Sun. Earthís atmosphere blocks much of the harmful light, but sunlight is still strong enough to burn skin under some conditions. Sunburn is one of the most important risk factors in the development of skin cancers, which can be fatal. Sunlight is also very harmful to human eyes. A person should never look directly at the Sun, even with sunglasses or during an eclipse. The Sun influences Earth with more than just light. Particles flowing from the Sun can disrupt Earthís magnetic field, and these disruptions can interfere with electronic communications.

Contributors

Levine, Randolph H., M.A., Ph.D.

Scientific Computing Marketing Manager, Digital Equipment Corporation. Author of "The Sun as Seen from Space". Contributor to "Solar Physics" and "Astrophysics Journal".

Lang, Kenneth R., B.S., B.A., M.S., Ph.D.

Professor of Astronomy, Tufts University. Visiting Senior Scientist, NASA Headquaters. Author of "Sun, Earth, and Sky" and "The New Sun".



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