Above the Sun's surface hang long ribbons of glowing gas — streamers. They look like giant harps stretched across the corona. When a wave runs along such a ribbon, it trembles and bends like a string after being plucked.
For a long time, it was thought that only a very fast ejection of material, one traveling at more than 500 kilometers per second, could launch such a wave. But new observations show that streamers respond to slow ejections as well. Two weak ejections in a row produced two waves that ran along the same ribbon of gas.
Both waves slowed down as they moved away from the Sun, but their rhythm remained almost the same: the oscillation period was about 2.5–2.7 hours. It's like two plucks of different strength producing the same note — because the note is set by the string itself, not by the strength of the pluck.
This discovery changes our view of how solar activity transfers energy into the corona. Even weak events can make large structures ring, and thus influence space weather around the Sun.
Streamers are visible during a total solar eclipse as long white rays spreading from the disk hidden by the Moon. Their shape resembles a helmet with feathers — hence the old name 'helmet streamers'.
In Arthur C. Clarke's novel 'Solar Wind', characters travel on a solar-sail yacht and must account for plasma gusts similar to those that run along streamers.