Nasa has released new footage showing a square ‘hole’ in the Sun captured by the space agency’s Solar Dynamics Observatory (SDO) spacecraft.

The phenomenon – known as a coronal hole – is perfectly normal and shows an area of the Sun’s corona that contains plasma with lower than average density. Nasa says that the coronal hole appears dark in the ultraviolet filter “as there is less material to emit in these wavelengths.”

The corona itself is made up of plasma expelled by the Sun and extends millions of kilometres into space. Although this is part of the Sun (much in the same way that the atmosphere can be said to be part of Earth) it's much hotter than the star's surface (between 150 and 450 times hotter) but produces only one-millionth as much visible light.

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Both solar flares and solar prominences (gigantic loop-shaped extrusions of gas that can be as big as the star's radius and linger for days) are found in the corona and are thought to be triggered and shaped by variations in the star's magnetic field.

In their description of the footage Nasa note that "inside the coronal hole you can see bright loops where the hot plasma outlines little pieces of the solar magnetic field sticking above the surface."

They also add that the position of the hole (“so far south on the Sun”) means there is “less chance that the solar wind stream will impact us here on Earth."

The footage comes from just one of Nasa's fleet of spacecraft assigned with watching the activities of the Sun. The SDO itself is on full-time star-watching duty and was launched in 2010 as the first craf in the space agency's Living With a Star program.