For a few weeks a year, a massive black shadow dashes across images captured by NASA’s Solar Dynamics Observatory. The observatory is technically only supposed to take pictures of the sun—but once in a while, Earth gets in the way.
The SDO orbits Earth, and captures images at roughly IMAX resolution (pdf). It typically enjoys a constant view of the sun, thanks to its position in a geosynchronous orbit. At this orbit, more than 20,000 miles above the earth, the satellite moves at the same speed as earth’s rotation; it is essentially able to stay in a static position above the Earth, rather than constantly moving around it like the International Space Station does. This, says NASA, allows the SDO to view the sun for the maximum amount of time possible.
But during the three-week “eclipse seasons” that occur around the year’s spring and fall equinoxes, the earth itself disrupts our constant surveillance of the sun. The images SDO transmits back during eclipses season show Earth passing in between its camera and the sun. Cleverly, NASA thought to record some of those brief eclipses in GIF format.
The different colors of the sun in these images are caused by scientists selectively viewing various wavelengths, and thus colors, of sunlight.
Yellow-green light of 5500 Angstroms, for example, generally emanates from material of about 10,000 degrees F (5700 degrees C), which represents the surface of the sun. Extreme ultraviolet light of 94 Angstroms, on the other hand, comes from atoms that are about 11 million degrees F (6,300,000 degrees C) and is a good wavelength for looking at solar flares, which can reach such high temperatures.