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.
The 100 millionth image captured by the Advanced Imaging Assembly on NASA's Solar Dynamics Observatory. It was taken on Jan. 19, 2015.
This "mosaic" image, also captured on Jan. 19, 2015, shows the sun in multiple wavelengths.
This photo shows a spectacular eruption on the sun. It was taken on June 7, 2011.
Taken Oct. 22, 2014, this SDO image shows an unusually large group of sunspots.
This false-color image from Oct. 24, 2014 shows magnetic fields produced by "coronal loops."
SDO captured this time-lapse photo showing Comet Lovejoy traveling around the sun in Dec. 2011.
This image was captured on Feb. 24, 2011. It shows a plume of plasma erupting from the sun's surface.
This image shows features on the sun that look a bit like a human face. The "eyes" show areas of hot material, the dark line of the "mouth" shows cooler material, and the "hair" around the outside illustrates material floating in the sun's atmosphere.
This three-color image was created with the help of a contrast-increasing filter. The dark spots represent the hotter regions.
NASA/SDO/Goddard Visualization Studio
This composite photo shows a rare transit of Venus as seen by SDO on June 5-6, 2012. The next Venus transit will occur on Dec. 10-11, 2117.
Sometimes the moon comes between SDO and the sun, as seen in this image taken on Nov. 22, 2014. If you look carefully, you can see that the edge of the moon is not a perfect circle--you can spot lunar mountains along the edge.
Captured on May 30, 2011, this two-part image shows an active region on the sun's surface where a moderate flare lights up a ridge in the region (left) and the difference between this exposure and an earlier one (right).
NASA/SDO/GSFC Visualization Studio
In this color wheel image, each color represents a different wavelength of extreme ultraviolet light present in the sun's corona.
NASA/SDO/Mosaic created with AndreaMosaic
A mosaic image of the 100 millionth image snapped by SDO's Atmospheric Imaging Instrument.