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The corona is hotter than the photosphere, despite being further from the Sun’s core. This has led to much head-scratching in the scientific community.
The sun's atmosphere, or corona - the wispy part we see during solar eclipses - is hundreds of times hotter than the sun's visible surface, or photosphere. Why?
London, May 25
The visible surface of the sun, or the photosphere, is around 6,000°C. But a few thousand kilometres above it – a small distance when we consider the size of the sun –
The visible surface of the sun, or the photosphere, is around 6,000°C. But a few thousand kilometres above it – a small distance when we consider the size of the sun – the solar atmosphere, also called the corona, is hundreds of times hotter, reaching a million degrees celsius or higher.
This spike in temperature, despite the increased distance from the sun’s main energy source, has been observed in most stars, and represents a fundamental puzzle that astrophysicists have mulled over for decades.
In 1942, the Swedish scientist Hannes Alfvén proposed an explanation. He theorised that magnetised waves of plasma could carry huge amounts of energy along the sun’s magnetic field from its interior to the corona, bypassing the photosphere before exploding with heat in the sun’s upper atmosphere.