These
spectacular photographs, taken at Caltech's solar observatory on Big Bear Lake,
record a particularly impressive solar flare on the surface of the sun on July
9, 1975. Although this is not a large
flare, the fact that we see it at the edge of the sun gives a better
understanding of the role of magnetic fields.
The first frame, at 22:44:00 universal time, shows the preflare
state. In this photograph in hydrogen
alpha light we know the bright area is a region of high magnetic field and
enhanced activity. The flare begins as
a bright blob at 23:34:24. As magnetic
fields reconnect and the magnetic stresses are relived, a twisted magnetic loop
filled with hot plasma rises from the surface.
As it rises further we see that there are many fine loops making up the
large one. Finally the loops break
up. The temperature in this flare,
measured by soft x-rays, is about 20 million degrees. The hole inside the loop is about twice the size of the earth.