File:SDOHMIdoppler sunspot.png

English: The Solar Dynamics Observatory (SDO) observes the Sun with many different instruments, in many different wavelengths of light. Many of these capabilities are not possible for ground-based observatories - hence the need for a space-based observing platform.

The Helioseismic Magnetic Imager (HMI) aboard the Solar Dynamics Observatory takes a series of images every 45 seconds in a very narrow range of wavelengths in visible light of the solar photosphere. The wavelengths correspond to a region around the 6173 Ångstroms (617.3 nanometers) spectral line of neutral iron (Fe I). From this series of images, it constructs a set of images which extract other characteristics of the photosphere. For this dataset, it measures the shifting of the spectral lines to determine the velocity of gas flows on the solar surface. This spectral line shift is due to the Doppler effect. Blue represents motion towards the observer. Red indicates motion away from the observer.

In images above, the color is dominated by the solar rotation, so the solar limb on the right is moving away from us (and therefore red) while the left limb is moving towards us (and therefore blue). Motions on the solar surface generate the rippling in the color and you can see evidence of surface flows around the sunspot near the left limb.