This sequence of 4 images shows the rapid formation and spreading of moss following a minor flare event. The blue circle in each image shows the approximate size of the Earth in the field-of-view. Image times are as follows.
1: 20:54 UT t = 0 seconds.
The bright "front" of moss advancing across the image moves with an average speed of about 17 km/sec (10 miles/sec or about 38,000 miles/hour). The moss forms in response to the spreading of the flare heat in the hot coronal loops above the moss; the loops are not visible in this TRACE 195 Angstrom image series because they are so hot that they radiate in x-rays, which are invisible to the TRACE instrument.