Williamina
Fleming
MAY 15, 1857
- MAY 21, 1911
Scottish astrono-
mer Williamina
Paton Stevens
Fleming discov-
ered the first
white dwarf
star, more than 50 nebulae (including
the Horsehead Nebula [Barnard 33]),
10 novae, and over 300 variable stars. But
she’s on this list primarily for her work on
the first Henry Draper Catalog, which list-
ed the spectral classifications of more than
10,000 stars as faint as 9th magnitude.
To tackle the job, Fleming developed
a scheme to order stars by the relative
amount of hydrogen in their spectra.
PORTRAIT: CURATOR OF ASTRONOMICAL PHOTOGRAPHS AT HARVARD COLLEGE
OBSERVATORY
14
George
Ellery Hale
JUNE 29, 1868 – FEB. 21, 1938
In 1908, American astronomer George Ellery Hale
proved that sunspots were associated with magnetic
fields — no small achievement. But what really
secured his place on this list were his tireless efforts
to fund and construct some of the most important
telescopes in the U.S. Among them are the 40-inch
refractor at Yerkes Observatory, the 60-inch and
100-inch ref lectors at Mount Wilson Observatory,
and the 200-inch ref lector at Palomar Observatory. The 200-inch was chris-
tened the Hale Telescope in his honor. Many of the 20th century’s greatest
astronomical discoveries are because of Hale. PORTRAIT: AIP EMILIO SEGRÈ VISUAL ARCHIVES13
Fred Hoyle
JUNE 24,
1915 –
AUG. 20,
2001
English astron-
omer Fred
Hoyle is best
known for his
theory of stellar nucleosynthesis — how
stars create elements heavier than heli-
um. Indeed, in 1946, he became the first
to write about this process. In 1954, he
produced another groundbreaking pub-
lication that showed how the elements
up to and including iron were produced
by fusion reactions in the cores of mas-
sive stars. Hoyle’s work also showed
how supernovae distribute heavy ele-
ments throughout the universe.
As a side note, Hoyle did not
embrace the Big Bang, but he did coin
the term, using it for the first time on a
BBC radio program in 1949. PORTRAIT: AIP EMILIO
SEGRÈ VISUAL ARCHIVES, PHYSICS TODAY COLLECTION
15
DEC. 16, 1857 – FEB. 6, 1923
Edward Emerson Barnard was arguably the greatest
visual observer ever. He discovered 17 comets, the
last of which was the first comet discovered using
photography. In 1916, Barnard measured the proper
motion of a magnitude 9.5 red dwarf in Ophiuchus.
He found a value of 10.3" per year, still the highest of
any known star. It’s now known as Barnard’s Star.
But Barnard’s greatest accomplishment was his
photographic atlas of the Milky Way. In it, he identified 349 dark regions pre-
viously thought to be voids between the stars. Barnard showed that these were
instead clouds of dust and cold gas — dark nebulae. PORTRAIT: AIP EMILIO SEGRÈ VISUAL ARCHIVES12
Maria Mitchell
AUG. 1, 1818 – JUNE 28, 1889
American astronomer Maria Mitchell rose to fame
by finding Miss Mitchell’s Comet (C/1847 T1). For
that discovery, which she made through a 3-inch
refractor on Oct. 1, 1847, she was presented a gold
medal by King Frederick VI of Denmark — becoming
the first woman to win an astronomy-related award.
Although she didn’t attend college, Mitchell was
appointed professor of astronomy and observatory
director at Vassar College in 1865. During her tenure, she became involved in
the anti-slavery and woman’s suffrage movements. Her efforts, and those of
the Maria Mitchell Association established after her death, helped many
women enter the fields of science and mathematics. PORTRAIT: AIP EMILIO SEGRÈ VISUAL ARCHIVES11
Edward Emerson
Barnard