Mankind's Version: Sun Spots
sunspots,
dark, usually irregularly shaped spots on the sun's surface that are actually
solar magnetic storms. The Chinese recorded dark features on the sun seen with
the naked eye in 28 B.C. Other observers including Kepler suspected that these
events might be transits of Mercury or Venus. Galileo observed them
systematically for several weeks before concluding that they had to be events
taking place on the solar surface. The temperature of the spots is lower than
that of the surrounding photosphere; thus the spots are darker. All but the
smallest show a dark central portion (the umbra) with a lighter outer area (the
penumbra). Studies of the spectra of sunspots show evidence of the Zeeman
effect, indicating the presence of a large magnetic field. In addition,
measurements of the Doppler
effect in the spectral lines show that there is a vortex motion in sunspots
similar to that of a tornado on earth. The lower temperature of the gases
constituting a sunspot results from the lower pressure due to the strong
magnetic field. Sunspots appear usually only between latitudes from 5° to 35°
north and south of the sun's equator. Sunspots are not permanent since the sun's
surface is gaseous. Because the sun rotates on its axis, a sunspot cannot be
observed continuously for more than about two weeks. In 1826 amateur astronomer
Heinrich Schwabe began a series of solar observations (in hopes of finding
planet Vulcan). By 1843 he had collected enough data to announce the existence
of the sunspot cycle. An 11-year cycle from one period of maximum activity to
the next is usually observed. However, a period during which most sunspots have
one magnetic polarity is followed by another period during which most have the
opposite magnetic polarity; thus, the cycle actually covers 22 years. During
each 11-year period sunspots appear first at higher latitudes and later at
latitudes closer to the solar equator as the period progresses. The spots often
form in pairs or groups, with a large, long-lived leader spot matched with one
or more smaller spots of opposite magnetic polarity. A number of phenomena are
associated with sunspots. Sunspot activity produces various disturbances on
earth-these include magnetic storms which manifest themselves as aurorae,
interference with radio reception and electric power grids, and disturbances of
the magnetic compass. Periods in which an increase in sunspots is observed are
called active periods. Reviewing historical records in 1890, E. Maunder noticed
that sunspot counts fell drastically between 1645 and 1715. In 1976 J. Eddy
correlated Maunder's data with a low frequency of aurorae and the reduced sizes
of annual tree rings. This "Maunder Minimum may have played a role in the
unusually low temperatures in the northern hemisphere during this period, which
is known as the Little Ice Age.