February 2013: The Busy Sun

Even near solar maximum, with sunspots dotting the photosphere, the Sun can look tranquil and serene in visible light. In the case of these images from the HMI instrument on the Solar Dynamics Observatory, the only obvious changes are the constant shimmering of the solar disk due to the bubbling of solar granulation.

But in ultraviolet light, in particular the 30.4 nanometer line of the helium ion, we see much more activity. Dark, wispy lines of cooler solar filaments (the term used for solar prominences when seen against the disk) stretch across the disk. The same structures, seen against the fainter glow of the solar corona, resemble slowly evolving flames on the limb of the Sun. Solar active regions surrounding the sunspots, appear bright in ultraviolet light.