A coronal hole

This ultraviolet image shows a coronal hole – the dark region in the centre – as seen by NASA’s Solar Dynamics Observatory (SDO) satellite.

Coronal holes are places where the Sun’s magnetic field is ‘open’, stretching deep into the Solar System and channeling solar wind out into space. These holes emit less ultraviolet light than their surroundings because the plasma (charged gas) inside is relatively cool and less dense.

Other regions of the Sun’s atmosphere, or corona, light up as plasma follows ‘closed’ magnetic field lines which arch between regions of opposite magnetic polarity on the Sun’s surface.

This image was taken on 24 February 2022 by SDO’s AIA instrument at a wavelength of 21.1 nanometres. Fast solar wind streaming out from this coronal hole was measured by the ESA-led Solar Orbiter mission and NASA’s Parker Solar Probe. Read more about their findings here.