First Centred Dopplergram
This frame is the first centered Dopplergram obtained with MDI. It was observed on 21 December 1995, shortly after the MDI protective door was opened.
The large left-right variation is the signal from Solar rotation. The Sun rotates with a period near 27 days (the equator goes faster, the poles slower) which means the surface is moving at about 2 km per second, or about 4500 miles per hour. The texture is a combination of the motion from the sound waves that permeate the Sun and the large (Earth-size) convective cells called "super-granulation". The primary science of SOI will be accomplished by analysis of many months of such velocity maps, one observed each minute. This image is the raw Dopplergram as computed on-board MDI (but reduced for this image)