Page 32 - Curriculum Visions Dynamic Book

Sunspot activity has a considerable effect on
the Earth. For example, a period of extremely low sunspot activity occurred at the same time as the Little Ice Age (around the 17th century), when glaciers spread out to cover parts of the northern continents. The last sunspot maximum was in 2002.
The chromosphere
Beyond the photosphere (the part of the
“atmosphere” of the Sun that we see as a bright
yellow disk) lies a small, even thinner part of the
atmosphere that shines less brightly. The Sun’s
atmosphere is faint in visible light but glows
brightly in ultraviolet light and in X-rays. It is
pink in colour (hence its name chromosphere); and because it is pale, it can only be seen during an eclipse.
The chromosphere is both very thin and very hot, the individual particles reaching temperatures up to 1,000,000°C.
Flares
A sudden release of magnetic energy at speeds of up to 1,500 kilometres per second can sometimes come from a sunspot to produce the most violent event on the Sun’s surface—a solar flare. Flares are closely connected to places where groups of very active sunspots occur.
Flares are invisible in ordinary light and can only be seen with strong coloured filters.
Flares occur where tangled magnetic field lines meet in the Sun’s atmosphere. If magnetic field lines meet going in opposite directions, they produce a magnetic short circuit, called a recombination.
A large flare can release as much energy as the entire
Sun normally does. Most of this energy is in the form of electrons and protons, and the light emitted is only
a secondary effect. The electrons heat up the surface and produce an immensely hot plasma, which moves out into the outermost atmosphere (the corona, see pages 35–37). That in turn produces X-rays and radio waves.
 This is an image taken from a film showing a solar quake. The white, feathery object in the center is the solar flare that caused the quake.
A solar flare is an explosion
in the atmosphere of the Sun caused by the tearing and reconnecting of strong magnetic fields. Although moderate
in size, this flare released an enormous amount of energy.
It produced the shock waves
of the solar quake, which can
be seen as concentric rings spreading outward from beneath the flare, much like ripples spreading from a rock dropped into a pool of water.
The flare-generated solar quake contained about
40,000 times the energy released in the great earthquake that devastated San Francisco in 1906.
The study of solar quakes is called helioseismology (see page 16).
32