William Herschel (Fig. 1) is rightfully known as one of the greatest astronomers of all time. Born in Hanover (in modern Germany) in 1738, Herschel immigrated to England in 1757 and began a successful career as a professional musician. Later in life Herschel developed a strong interest in astronomy. He began making his own reflecting telescopes in 1774, and soon his telescopes were recognized as the finest in the world. It was through one of his homemade telescopes, a Newtonian reflector with a focal length of seven feet and an aperture of 6.2 inches, that Herschel first spotted the planet Uranus in 1781. The discovery of a new planet catapulted Herschel to fame and secured him a position as personal astronomer to King George III.

1.

Herschel's diagram can be found in most introductory astronomy textbooks, and his work is listed as item 5 (Disk of Stars) in the astronomy section of the Discovery Channel's “100 Greatest Discoveries,” science.discovery.com/videos/100-greatest-discoveries-astronomy/.

2.
A notable exception is Bless,
Discovering the Cosmos
(
University Science Books
,
1996
), which provides an accurate description of Herschel's approach.
3.

One example is Pierre Gassendi, who recorded this idea in lecture notes that were not published until his death in 1655.

4.
W.
Herschel
, “
Account of some observations tending to investigate the construction of the heavens
,”
Philos. Trans. R. Soc. London
74
,
437
451
(
1784
).
5.
W.
Herschel
, “
On the construction of the heavens
,”
Philos. Trans. R. Soc. London
75
,
213
266
(
1785
).
6.

The Herschel's Star Gages EJS model is available from www.compadre.org/osp/items/detail.cfm?ID=11214. An activity worksheet designed for use with this simulation is available as a supplemental document on the same page.

7.

The simulation assumes a telescope with a 0.1 radian (5.7°) field of view.

8.

Note that the jagged edges of the star gages are due to random fluctuations in the star counts. The limited distance star gages appear more jagged because these fluctuations scale like the square root of N, where N is the number of stars in the count. Smaller counts will have relatively larger fluctuations.

9.
W.
Herschel
, “
Astronomical observations and experiments tending to investigate the local arrangement of the celestial bodies in space, and to determine the extent and condition of the Milky Way
,”
Philos. Trans. R. Soc. London
107
,
302
331
(
1817
).
10.
See
M.
Hoskin
,
The Construction of the Heavens: William Herschel's Cosmology
(
Cambridge University Press
,
Cambridge, UK
,
2012
) for several of Herschel's papers and commentary by Hoskin.
For an in-depth look at the lives of William and Caroline Herschel, see
M.
Hoskin
,
Discoverers of the Universe
(
Princeton University Press
,
Princeton, NJ
,
2011
).
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