NASA’s Solar Dynamics Observatory spotted a cheerless face in the sun last month. The frown, complete with a down-turning of the mouth, was created by a solar filament that had snaked across the lower half of the sun on February 10. Stretched out, the filament would have been longer than 67 Earths lined up side-by-side in a row.
Solar filaments are made of plasma, or electrified gas, and they usually appear above magnetically disturbed regions called sunspots. Sometimes filaments calmly float above the sun’s surface for days (even months), then simply disappear. Other times, they can erupt and release solar material that either showers back down or escapes out into space—resulting in a moving cloud known as a coronal mass ejection.
The Solar Dynamics Observatory (SDO) shows colder material as dark and hotter material as lighter. That means the frown hovering in the sun's atmosphere (or the corona) is much colder than the surface behind it. Stretched out, that solar filament would be more than 858,000 kilometers (533,000 miles) long, according to a NASA Goddard Space Flight Center news release.
SDO captured images of the filament in multiple wavelengths, and each of these highlight solar material of varying temperatures. Studying these different wavelengths and temperatures help scientists understand what causes these structures and why they occasionally erupt.