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All About the Sun's Light

The sun holds the dominant position in our solar system, occupying more than 99 percent of the solar system's total mass. Many stars in other galaxies are similar in size to the sun; however, the sun sits in the upper 10 percent when comparing the sizes of all stars in the universe. The sun contains approximately 70 percent hydrogen and 28 percent helium, with metals making up the remainder of the sun's composition. The sun is not a solid mass; instead, it is made up of gases that move continually. The sun provides heat and light for the Earth, generating weather patterns and sustaining plants that provide food and oxygen for life on Earth.

How Sunlight is Created

The temperature at the center of the sun can reach in excess of 27 million degrees Fahrenheit through the process of nuclear fusion. Energy radiates out from the core of the sun to the outer layers. The outer, visible layer of the sun is called the photosphere. The photosphere has temperatures of approximately 10,000 degrees Fahrenheit. The photosphere releases the sun's energy, which the bodies and planets in the solar system receive as sunlight. The intense heat of the photosphere makes it appear bright and without color.

How the Sun Heats the Earth

The energy emitted by the sun travels through space. Once this heat reaches the Earth, the planet absorbs it. This process is called radiation or heat transfer. Soil, plants, concrete, and even humans and animals absorb the sun's heat. The sun's heat also warms molecules in the atmosphere, which go on to spread the heat to other molecules. This process is known as conduction. Conduction works to maintain the Earth's temperature around the clock, even during overnight hours when sunlight is absent. Convection is the process by which the sun's energy warms liquids and gases. Convection can produce clouds, air currents, and thermal cells that transfer heat to the atmosphere.

The Greenhouse Effect

Earth enjoys relatively stable temperatures, thanks to the atmosphere that surrounds and protects it. These atmospheric gases include nitrogen, oxygen, argon, and carbon dioxide. As the sun produces energy that heats Earth, the planet reacts by producing infrared radiation, which helps maintain its temperature. Infrared radiation travels out from Earth into space, where it disperses the heat. Human life on Earth has produced a variety of other gases, which hang in the atmosphere. These gases include carbon dioxide, nitrous oxide, methane, and water vapor. While these gases allow radiation from the sun through to reach the earth, the weaker infrared radiation from the surface does not penetrate these gases as effectively to leave the Earth. The end result is the containment of heat near the ground, which raises Earth's overall temperature.

Sunlight and Weather

Weather includes the amount of cloud cover, temperature, precipitation, and the air pressure. The sun's energy in Earth's atmosphere has a profound impact on weather. The sun's heat is most intense at the equator, and it is the weakest at the south and north poles. Temperature differences between the equator and the poles create air currents, which help to distribute the sun's energy throughout the surface of the planet. The sun is also responsible for seasonal changes in weather because of Earth's tilt on its axis and because Earth revolves around the sun continually. Whatever hemisphere of the planet is tilted closest to the sun has summer, while the opposite hemisphere tilted away from the sun has winter. The sun also plays a role in the water cycle, which produces precipitation. When the sun heats up bodies of water on Earth, evaporation occurs and water vapor moves up into the atmosphere. Condensation occurs next, and clouds form in the sky. The clouds will fill with moisture until they eventually become so full that they release it, causing precipitation to fall in the form of rain or snow.

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