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The Sun's corona is much hotter (by a factor from 150 to 450) than the visible surface of the Sun: the corona's temperature is 1 to 3 million kelvin compared to the photosphere's average temperature – around 5 800 kelvin. The corona is far less dense than the photosphere, and produces about one-millionth as much visible light.
Density in the corona generally decreases with height above the visible "surface", or photosphere, meaning that lower-frequency emission is produced higher in the atmosphere, and the Sun appears larger at lower frequencies. This type of emission is most prominent below 300 MHz due to typical coronal densities, but particularly dense structures ...
Prominences are anchored to the Sun's surface in the much brighter photosphere, and extend outwards into the solar corona. While the corona consists of extremely hot plasma, prominences contain much cooler plasma, similar in composition to that of the chromosphere.
Coronal loops begin and end at two footpoints on the photosphere and project into the transition region and lower corona. They typically form and dissipate over periods of seconds to days [1] and may span anywhere from 1 to 1,000 megametres (621 to 621,000 mi) in length. [2]
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.
In solar physics and observation, granules are convection cells in the Sun's photosphere. They are caused by currents of plasma in the Sun's convective zone, directly below the photosphere. The grainy appearance of the photosphere is produced by the tops of these convective cells; this pattern is referred to as granulation.
The corona extends much further than a solar radius from the photosphere and looks very complex and inhomogeneous in the X-rays images taken by satellites (see the figure on the right taken by the XRT on board Hinode). The structure and dynamics of the corona are dominated by the solar magnetic field.
A radiative zone is a layer of a star's interior where energy is primarily transported toward the exterior by means of radiative diffusion and thermal conduction, rather than by convection. [1]