The Sun’s active regions: coronal rain and solar moss


The Extreme Ultraviolet Imager (EUI) on the ESA/NASA Solar Orbiter spacecraft captured this movie on 17 March 2022. It shows the Sun’s appearance at a wavelength of 17 nanometers. This is an extreme ultraviolet wavelength of light that is emitted by the upper atmosphere of the Sun. Known as the corona, this layer of the Sun’s atmosphere exists at a temperature of around one million degrees. EUI takes both full disc images using the Full Sun Imager (FSI) telescope, as well as detailed images of a smaller region using the High Resolution Imager (HRIEUV) telescope.

On 17 March, Solar Orbiter was at roughly a third of the Earth’s distance from the Sun (0.378 AU), and heading for a close approach on 26 March, placing its payload closer to the Sun than any previous solar telescope.

This movie shows FSI’s view of the Sun before zooming in on an active region with HRIEUV. Active regions are where the Sun’s magnetic field bursts out from its interior in loops that rise into the atmosphere. As gas flows around the loops and cools back down on its way to the surface it creates the phenomenon called coronal rain.

Another intriguing feature of this image is the bright gas that makes delicate, lace-like patterns across the Sun. This is called coronal ‘moss’. It usually appears around the footprints, referred to by solar physicists as footpoints, of large coronal loops that are too hot to be seen in the EUI images.

The colour on this image has been artificially added because the original wavelength detected by the instrument is invisible to the human eye.

Credit: ESA & NASA/Solar Orbiter/EUI Team

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