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Space and Sky · entry 47 of 52
The Sun's corona is far hotter than its visible surface, for reasons still debated.
The longer version
The corona puzzles astronomers because temperatures there reach millions of degrees while the visible surface below sits far cooler. Heat normally flows outward from a hotter region to a cooler one, so something must be pumping energy into the outer atmosphere. The glow is faint compared with the disk and normally hidden.
Leading ideas involve magnetic waves traveling outward and small, frequent magnetic reconnection events that release stored energy. The solar wind also originates in these hot outer layers. Spacecraft and eclipses both provide ways to study the region, though questions remain about the balance of mechanisms. No single explanation has been confirmed.
Where this entry sits
The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.
More From Space and Sky
Eight more entriesMeteorites often come from asteroids, though a few originated on Mars or the Moon.
Read 49Starlight reaching Earth tonight left its star years or even centuries earlier.
Read 50Planets do not produce visible light of their own; they shine by reflecting sunlight.
Read 51Earth is the only planet known to hold liquid water across much of its surface.
Read 52The Moon has no atmosphere, so surface tracks there can remain for millions of years.
Read 1The Sun contains roughly ninety-nine percent of all the mass in the solar system.
Read 2Light from the Sun takes about eight minutes to reach our planet.
Read 3Ocean tides are caused mainly by the Moon pulling on Earth's water.
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