On February 21, 2012, the Moon moved in between NASA’s Solar Dynamics Observatory (SDO) satellite and the Sun (seen here in extreme ultraviolet light) and produced a partial solar eclipse from space. The SDO team observed the lunar transit, which began at about 8.10 am EST and ended about 10 am EST. While this event only happens a few times a year, it gives the SDO team an opportunity to fine-tune the AIA instrument onboard the spacecraft.
The sharp edge of the lunar limb helps researchers measure the in-orbit characteristics of the telescope, e.g., how light diffracts around the telescope's optics and filter support grids. Once these are calibrated, it is possible to correct SDO data for instrumental effects and sharpen the images it produces.