The surface of the sun is constantly changing. To make sure it doesn't miss anything, NASA's Solar Dynamics Observatory (SDO) spacecraft is constantly taking photos of the sun.
One of the three instruments aboard the spacecraft, the four-telescope Atmospheric Imaging Assembly, is especially prolific; it takes a mind-boggling 57,000 photos a day. And at 12:49 p.m. ET on Jan. 19, 2015, it snapped its 100 millionth photo.
To mark the occasion, a pair of scientists involved with the mission selected their favorite SDO images taken so far.
Scroll down to see the 100 millionth image and a "mosaic" image captured on the same day--followed by the scientists' favorites.