526 PART 4^ |^ THE SOLAR SYSTEM
A good many things go around in the dark
besides Santa Claus.
— HERBERT HOOVERO
ut in the darkness beyond Saturn, out where sun-
light is 1000 times fainter than on Earth, there are
objects orbiting the sun that Aristotle, Galileo, and
Newton never imagined. Th ey knew about Mercury, Venus, Mars,
Jupiter, and Saturn, but our solar system also includes worlds that
were not discovered until after the invention of the telescope. Th e
stories of those discoveries highlight the process of scientifi c dis-
covery, and the characteristics of these dimly lit worlds will reveal
more of nature’s secrets from the birth of the solar system.
Uranus
In March 1781, Benjamin Franklin was in France raising
money, troops, and arms for the American Revolution. George
24-1
Washington and his colonial army were only six months away
from the defeat of Cornwallis at Yorktown and the end of the
war. In England, King George III was beginning to show signs of
madness. And a German-speaking music teacher in the English
resort city of Bath was about to discover the planet Uranus.The Discovery of Uranus
William Herschel (■ Figure 24-1) came from a musical family in
Hanover, Germany, but emigrated to England as a young man
and eventually obtained a prestigious job as the organist at the
Octagon Chapel in Bath.
To compose exercises for his students and choral and organ
works for the chapel, Herschel studied the mathematical princi-
ples of musical harmony from a book by Professor Robert Smith
of Cambridge. Th e mathematics in the book were so interesting
that Herschel searched out other works by Smith, including a
book on optics. Of course, it is not surprising that an 18th-cen-
tury book on optics written by a professor in England relied
heavily on Isaac Newton’s discoveries and described the principles■ Figure 24-1
(a) When William Herschel discovered Uranus in 1781,
he saw only a tiny green-blue dot. He never knew how
interesting that planet is. Even the designer of this
stamp marking the passage of Comet Halley in 1986 had
to guess at the planet’s appearance. (b) An image of
Uranus recorded by a near-infrared camera on the Keck
telescope shows banding and cloud features. Seasonal
changes are observed on Uranus as spring comes to
the northern hemisphere. The rings look red in this
view because of image processing. (Lawrence Sromovsky,
UW-Madison Space Science and Engineering Center)
b Enhanced infrared imagea