DIRECTORY 337
sunspots uncovered a correlation
between their number and Earth’s
climate. This led them to discover
a period of reduced solar activity
between 1645 and 1715, now called
the Maunder Minimum, which
coincided with lower-than-average
temperatures in Europe. When the
ban on women at the society was
lifted in 1916, Annie Maunder
was elected a Fellow of the Royal
Astronomical Society, after
which her observations were
published under her own name.
Prior to that, much of her work
had appeared in papers under
her husband’s name.
See also: The surface of the sun
103 ■ The properties of sunspots 129E. E. BARNARD
1857–1923US astronomer Edward Emerson
Barnard was a renowned observer,
who discovered about 30 new
comets and numerous nebulae.
In 1892, Barnard discovered
a fifth moon around Jupiter, called
Amalthea, which was to be the
last moon to be discovered through
visual observation rather than
through the study of photographic
plates. Himself a pioneer of astro-
photography, Barnard produced
a series of stunning long-exposure
photographs of the Milky Way,
which was published posthumously
in 1927 as the Atlas of Selected
Regions of the Milky Way. Barnard’s
star is named after him; in 1916, he
discovered that this faint red dwarf
has the largest known proper motion
(rate at which a star changes its
position on the celestial sphere)
of all known stars.
See also: Galileo’s telescope
56–63 ■ Astrophotography
118–19HEBER D. CURTIS
1872–1942American classics professor Heber
Doust Curtis switched to astronomy
in 1900 when he became a volunteer
observer for the Lick Observatory in
California. After receiving his Ph.D.
in astronomy in 1902, Curtis enjoyed
a long association with the Lick
Observatory, carrying out a detailed
survey of the known nebulae, which
he completed in 1918. In 1920, he
took part in the “Great Debate” with
fellow astronomer Harlow Shapley
at the Smithsonian museum. Curtis
argued that distant nebulae were
separate galaxies far from the Milky
Way, while Shapley asserted that
they lay within it.
See also: Spiral galaxies 156–61 ■
Beyond the Milky Way 172–77JAMES JEANS
1877–1946British mathematician James Jeans
worked on a variety of theoretical
problems relating to astrophysics. In
1902, he calculated the conditions
under which a cloud of interstellar
gas becomes unstable and collapses
to form a new star. In developing his
theory of gases in 1916, he explained
how gas atoms can gradually escape
from a planet’s atmosphere over time.
In later life, Jeans devoted his time to
writing and became well-known for
his nine popular books, including
Through Space and Time and The
Stars in Their Courses. He promoted
an idealist philosophy that saw
both mind and matter as central to
understanding the universe, which
he described as “nearer to a great
thought than to a great machine.”
See also: Inside giant molecular
clouds 276–79photography began to be taken
seriously by astronomers as a means
of discovery. After his death, his wife
created a foundation in his name,
which funded the Henry Draper
Catalogue, a huge photographic
survey of the stars carried out by
Edward C. Pickering and his team
of female astronomers.
See also: The star catalog
120–21 ■ The characteristics of
the stars 122–27
JACOBUS KAPTEYN
1851–1922
Using photographic plates supplied
to him from South Africa by David
Gill, Dutch astronomer Jacobus
Kapteyn cataloged more than
450,000 southern stars. After
grouping stars in different parts
of the galaxy and measuring their
magnitudes, radial velocities, and
proper motions, Kapteyn carried out
vast statistical analyzes that revealed
the phenomenon of star streaming—
which shows how the motions of
stars are not random, but grouped
together in two opposite directions.
This was the first definitive evidence
that the Milky Way galaxy is rotating.
See also: Astrophotography
118–19
EDWARD WALTER MAUNDER
1851–1928
ANNIE SCOTT DILL
MAUNDER
1868–1947
British husband and wife team
Edward Walter Maunder and
Annie Maunder (née Scott Dill)
collaborated at the Greenwich
Royal Observatory in the study
of the sun. Their investigations of