HMI Roll Tonight

Tonight, April 9, 2014, from 0519-1200 UTC (1:19 am - 8:00 am ET). SDO will execute the HMI Roll maneuver. The spacecraft will spin 360 degrees about the line to the Sun center. It stops along the way to collect a few images at each of the points. Usually the near-realtime images that are served from the SDO website are "de-rotated", but sometimes we get the watch the Sun spin around.

This data is used to study how the instruments change while they are on orbit. The most important science that comes out is whether the Sun is round or bulges a little bit at the waist. So far, it appears that the Sun bulges less than we expect and that bulge does not change very much as sunspots come and go. The only way to check is to redo the measurements at different times in the solar cycle. This set of points will be made at the maximum of Solar Cycle 24.