Our Sun may be made up of 98% hydrogen and helium but the remaining two percent comprises many other elements, detectable by their unique absorption lines within the gamut of white light we receive on Earth. One of those elements is calcium, which exists in ionized form in relatively tiny amounts in the Sun’s chromosphere – but still enough to allow images to be made using special filters aligned to the wavelength of its absorption line. And this is precisely what photographer Alan Friedman did on April 12, 2015 when he captured the image above!
Taken in the calcium K-line (aka Ca II K) the view above shows features of our Sun’s chromosphere that would otherwise be invisible in white light, such as the fine granulation textures, bright regions called chromospheric plages, and the entire web-like “craquelure” structure of the chromospheric network.
Active region 2321 can be seen as it was coming into view along the Sun’s northern limb at left.
Because images like these are captured in single monochromatic channels (i.e., black-and-white) they must be assigned colors to make a view like this. Thankfully Alan is an artist and has no problems doing this to create a gorgeous image!
Click the picture to see it in high-resolution on Alan’s Averted Imagination portfolio site, and learn more about CaK photography (and hydrogen alpha – Ha – photography, which Alan also specializes in) here.
Image © Alan Friedman. All rights reserved.