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The Sun's atmosphere

This picture shows the plasma (superheated gas) making up the sun's atmosphere at different temperatures, and therefore heights away from the solar surface. There are still two main competing theories on why the sun's atmosphere gets hotter with height away from the surface of the sun.

The different colours range from the photosphere, the sun's visible surface (around 5,000°C) at the bottom, through the chromosphere (around 50,000°C) in the middle, to the outer corona (around six million °C) at the top.

Some of the corona is bound to the sun by its magnetic field. However it is so hot that some of it also blows out into space, creating the solar wind, which streams outwards past the planets, including Earth, to create a bubble containing the whole solar system - the heliosphere.

To fully wrap round the sun, images from NASA's Solar Dynamics Observatory satellite have been stitched together at successive quarter solar rotations. The result looks relatively continuous as the sun's atmosphere is often quite static on solar rotation timescales (27 days). This stability is used in forecasts in the Met Office Space Weather Operations Centre (MOSWOC), which has just celebrated its first birthday.

The sun isn't always calm though - MOSWOC uses the unstitched images to monitor solar activity. This includes looking for solar flares, or sudden movements of the plasma, which herald space weather which could lead to impacts on satellites or power grids.