The sunlight that we cannot see

International Year of Light Blog

Imagine the Sun’s surface as an utterly black sphere. Imagine a cloudscape above this that is comprised of colorful fans of glowing wisps of translucent fog, all vastly larger than the Earth, which are continually swaying and pulsing, occasionally being torn apart by lightning storms of literally astronomical proportions.

Difficult? Not with some of the remarkable telescopes onboard NASA’s Solar Dynamics Observatory (SDO). They see that dynamic cloudscape, the Sun’s outer atmosphere, all the time, every day of the year, taking a picture almost every second over the past five years. These telescopes look at the Sun’s extreme ultraviolet (EUV) glow. That glow comes only from parts of the Sun’s atmosphere where the temperature exceeds a million degrees. Not from the solar surface that is  ‘merely’ a few thousand degrees, and that consequently is simply black in SDO’s EUV images.

Images taken by NASA’s Solar Dynamics Observatory on October 24, 2014. The image on the left shows the Sun’s hot atmosphere in extreme ultraviolet (EUV) light, with colors measuring temperature: blue is about 1.1 million degrees Celsius, green about 1.6 million, and red 2.2 million. The image on the right is taken in visible light at the same time, showing how we would see the Sun if viewed with a safe telescope. The sunspots seen on that day were the largest in over 25 years; the Earth would easily fit into the dark core of the largest spot. Credit NASA Images taken by NASA’s Solar Dynamics Observatory on October 24…

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