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ESA Space news: The colour sphere of the Sun

This colourful image, released earlier today as ESA’s Space Science Image of the Week is a chromosphere flash spectrum captured during the total solar eclipse that could be seen across the United States on 21 August 2017.

The image was taken by ESA’s expedition team who monitored the eclipse from Casper, Wyoming (Copyright ESA/M. Castillo-Fraile).

During an eclipse, when the Moon temporarily partially blocks the light from the Sun, astronomers can make unique measurements. This includes looking at and analysing the normally invisible red hue of the chromosphere.

What is the Sun’s chromosphere?
The sun is made up of different layers (see image below)

(Image Credit: NASA)

The chromosphere is a layer in the Sun between about 250 miles (400 km) and 1300 miles (2100 km) above the solar surface. The technical name for the surface of the sun that we can see, where sun spots and solar flares are sometimes visible, is called the photosphere.

The chromosphere sits above the photosphere and emits a reddish glow as super-heated hydrogen burns off. But the red rim can only be seen during a total solar eclipse. At other times, light from the chromosphere is usually too weak to be seen against the brighter photosphere.

Just before and after the eclipse totality, the Sun’s emission can be split into a spectrum of colours, showing the fingerprint of different chemical elements.

(The colour sphere of the Sun. An image of the eclipsed Sun is produced to the left, and the spectrum of each point of the Sun superposed at the right. Credit: ESA/M. Castillo-Fraile)

The strongest emission is due to hydrogen. The bright yellow corresponds to helium, an element only discovered in a flash spectrum captured during the 18 August 1868 total eclipse, although it was then unknown what it was. Nearly three decades later the element was discovered on Earth and helium is now known to be the second most abundant element in the Universe, after hydrogen.

The image was taken by astronomers from the Cesar science educational project based at ESA’s European Space Astronomy Centre near Madrid in Spain. For more eclipse images and technical information visit the Cesar eclipse website.

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