Sunlight

SUNLIGHT IS THE electromagnetic radiation given off by the sun. It is passed through the atmosphere to the Earth, where the solar radiation is reflected as daylight. Sunshine results when the solar radiation is not blocked. Sunlight is the primary source of energy to the Earth. It provides infrared, visible, and ultraviolet (UV) electromagnetic radiation with different wavelengths. Small sections of the wavelengths that are visible to the human eye are reflected as rainbow colors. Sunlight may be recorded using a sunshine recorder. Electromagnetic waves are waves that are capable of transporting energy through the vacuum of outer space and that exist with an enormous continuous range of frequencies known as the electromagnetic spectrum. The spectrum is divided into smaller spectra on the basis of interactions of electromagnetic waves with matter.

Sunlight is Earth's primary source of energy, providing infrared, visible, and ultraviolet electromagnetic radiation.

The longer-wavelength, lower-frequency regions are located on the far left of the spectrum, and the shorter-wavelength, higher-frequency regions are on the far right. Two very narrow regions within the spectrum are the visible light region and the X-ray region. The visible light region is a very narrow band of wavelengths located to the right of the infrared region and to the left of the UV region. Though electromagnetic [Page 938]waves exist in a vast range of wavelengths, human eyes are only sensitive to the visible light spectrum. The visible portion of the solar spectrum lies between 400 and 700 nm. and separates the UV region of shorter wavelengths from the infrared region of longer wavelengths. A combination of waves results in white light. Red has the longest visible wavelength, whereas violet has the shortest. Waves longer than red are known as infrared, and waves shorter than violet are called UV.

The sun is the closest star to the Earth and the most closely studied. It is at the center of the solar system and accounts for about 99.8 percent of the mass of the solar system. The planets revolve around the sun. The sun is composed of hydrogen, helium, and other trace elements and goes around the center of the Milky Way galaxy at a distance of about 26,000 light years from the center of the galaxy. The amount of solar energy incident on the Earths atmosphere is about 342 Watts per sq. m.r, based on the surface area of the Earth. Although the Earths surface continuously radiates energy outward to space, only part of the surface area receives solar radiation at a time. Most of the solar energy incident on the Earth is in the UV region of shorter wavelengths. The sun is the source of heat that sustains life on Earth and controls the climate and weather. Only the sun's outer layers, which consist of the photosphere, the chromosphere, and the corona, can be observed directly. These three regions have different properties from one another, with regions of gradual transition between them. The sun has basically the same chemical elements as are present on the Earth. However, the sun is so hot that all of these elements exist in the gaseous state. Energy generated in the sun's core takes a million years to reach its surface. Solar energy is created deep within the core of the sun, where nuclear reactions take place.

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