103
See also: Observing Uranus 84–85 ■ The properties of sunspots 129 ■
Carrington (Directory) 336S
unspots are cooler areas
on the sun’s surface caused
by changes in its magnetic
field. The first written observations
of sunspots date from about 800 bce,
in China, but it was not until 1801
that the British astronomer William
Herschel made the connection
between sunspots and changes
in Earth’s climate.
Samuel Schwabe, a German
astronomer, started observing
sunspots in 1826. He was looking
for a new planet thought to orbit
closer to the sun than Mercury,
provisionally named Vulcan. It
would have been very difficult to
observe such a planet directly, but
Schwabe thought he might see it
as a dark spot moving in front ofthe sun. He did not find Vulcan, but
he did discover that the number of
sunspots varied over 11-year cycles.
Swiss astronomer Rudolf Wolf
studied Schwabe’s and other
observations, including some
from as far back as Galileo, and
numbered the cycles starting at
1 for the 1755–66 cycle. Eventually,
he saw that there are long periods
in each cycle when the number of
sunspots is low. Herschel had not
noticed the pattern because he was
observing during what is now called
the Dalton Minimum, when overall
numbers of sunspots were low. ■URANUS TO NEPTUNE
SUNSPOTS
APPEAR IN
CYCLES
THE SURFACE OF THE SUN
IN CONTEXT
KEY ASTRONOMER
Samuel Heinrich Schwabe
(1789 –1875)
BEFORE
800 bce Chinese and Korean
astrologers record sunspots
to help foretell events.
1128 English chronicler John
of Worcester draws sunspots.
1801 William Herschel links
sunspot numbers and the price
of wheat, due to the effect of
sunspots on Earth’s climate.
AFTER
1845 French physicists
Hippolyte Fizeau and Léon
Foucault photograph sunspots.
1852 Irish astronomer Edward
Sabine demonstrates that the
number of magnetic storms
on Earth correlates with the
number of sunspots.
1908 US astronomer George
Ellery Hale discovers that
sunspots are caused by
magnetic fields.
Sunspots can last from a few
days to several months. The largest
can be the size of Jupiter.