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The Sun's atmosphere is composed of five layers: the photosphere, the chromosphere, the transition region, the corona, and the heliosphere. The coolest layer of the Sun is a temperature minimum region extending to about 500 km above the photosphere, and has a temperature of about 4,100 K. [77]
A wood carving from 1475, showing 7 celestial bodies. The 5 planets that can be seen with the naked eye, and the Sun and the Moon, each floating in a heavenly layer, the Arabic Felaq in ancient cosmology. In mythological or religious cosmology, the seven heavens refer to seven levels or divisions of the Heavens.
In the Sun, the region between the solar core at 0.2 of the Sun's radius and the outer convection zone at 0.71 of the Sun's radius is referred to as the radiation zone, although the core is also a radiative region. [1] The convection zone and the radiative zone are divided by the tachocline, another part of the Sun.
It was also contacted in 2003 when it was a distance of 7.6 billion miles from Earth (82 AU), but no instrument data about the solar wind was returned then. [68] [69] Voyager 1 surpassed the radial distance from the Sun of Pioneer 10 at 69.4 AU on 17 February 1998, because it was traveling faster, gaining about 1.02 AU per year. [70]
Below, gravity tends to dominate the shape of most features, so that the Sun may often be described in terms of layers and horizontal features (like sunspots); above, dynamic forces dominate the shape of most features, so that the transition region itself is not a well-defined layer at a particular altitude.
Some 91% of the solar energy is produced within this radius. Within 24% of the radius (the outer "core" by some definitions), 99% of the Sun's power is produced. Beyond 30% of the solar radius, where temperature is 7 million K and density has fallen to 10 g/cm 3 the rate of fusion is almost nil. [7]
Its outer layers will be ejected into space, leaving behind a dense white dwarf, half the original mass of the Sun but only the size of Earth. [30] The ejected outer layers may form a planetary nebula, returning some of the material that formed the Sun—but now enriched with heavier elements like carbon—to the interstellar medium. [33] [34]
The Sun is composed primarily of the chemical elements hydrogen and helium; they account for 74.9% and 23.8%, respectively, of the mass of the Sun in the photosphere.All heavier elements, colloquially called metals in stellar astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.