| • Science | • People | • Locations | • Timeline |
Solar radiation is thermal radiation emitted from the surface of the sun, which is powered by nuclear fusion.
Solar radiation is commonly measured with a pyranometer or pyrheliometer.
The average energy density of solar radiation just above the Earth's atmosphere, in a plane perpendicular to the rays, is about 1367 W/mē, a value called the solar constantThe solar constant is the amount of incoming solar radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays. It is measured by satellite to be roughly 1367 watts per square metre. Thus, for the who (although it fluctuates by a few parts per thousand from day to day). Because the surface area of a sphereFor other uses, see sphere (disambiguation). A sphere is, roughly speaking, a ball-shaped object. In non-mathematical usage a sphere is often considered to be solid (which mathematicians call ball . But in mathematics, a sphere is the boundary of a ball, is 1/4 of the surface area of its cross-section, the temporally and spatially averaged insolationInsolation is the incoming solar radiation that reaches a planet and its atmosphere. Also see diffuse insolation and direct insolation. External link . over the Earth's surface above the atmosphere is a quarter of this value, 342 W/mē. At any given location and time, the amount received at the surface depends on the state of the atmosphere and the latitudeLatitude denoted φ, gives the location of a place on Earth north or south of the Equator. Latitude is an angular measurement ranging from 0° at the Equator to 90° at the poles. Usually, the difference in latitude largely affects the climate and/or wea.
On Earth, solar radiation is obvious as daylight when the sun is above the horizonFor the television programme called Horizon, see Horizon (television). The horizon is the line that separates earth from sky. More precisely, it is the line that divides all of the directions you can possibly look into, into two categories: those which in. This is during daytime, and also in summerSummer is one of the four temperate seasons. Astronomically, it begins with the summer solstice (around 21 June in the Northern hemisphere, and 21 December in the Southern hemisphere) and ends with the autumn equinox (around 21 September in the Northern h near the poles at nightThis article describes the time of day. For the work by Elie Wiesel, see Night (book . Night is the time when a location is facing away from the Sun, and thus dark. On Earth, it is night on just under half the planet at any time. The atmosphere refracts s, but not at all in winterThis article is about the winter season. For other uses of the term, see winter (disambiguation). Winter is one of the four seasons of temperate zones. Astronomically, it begins with the winter solstice (around December 21 in the Northern hemisphere and J near the poles. When the direct radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright yellow light (sunlight in the strict sense) and heat. The heat on the body, on objects, etc., that is directly produced by the radiation should be distinguished from the increase in air temperature.
The amount of radiation intercepted by a planetary body varies as the square of the distance between the star and the planet. The Earth's orbit and obliquity change with time, sometimes achieving a nearly perfect circle, and at other times stretching out to an eccentricity of 5%. The total insolation remains almost constant but the seasonal and latitudinal distribution and intensity of solar radiation received at the Earth's surface also varies (for example see a graph). For example, at latitudes of 65 degrees the change in solar energy can vary by more than 25% as a result of the Earth's orbital variation. Changes associated with the redistribution of solar energy are considered a likely cause for the coming and going of recent ice ages (see: Milankovitch cycles).