Harlow Shapley
NOV. 2, 1885 –
OCT. 20, 1972
American astronomer Harlow
Shapley was instrumental in
popularizing the idea that
Cepheid variables changed their
brightness because they pulsate
and not because they’re binary
stars. He studied the distribution of globular clusters and
showed that the Sun wasn’t at the center of the Milky
Way. He also proposed the liquid water belt theory,
which said that a planet had to orbit at a given distance
from its star to host liquid water. This region is now
known as the habitable zone.
Probably best known for his participation in the Great
Debate with astronomer Heber D. Curtis, Shapley took
the wrong side as he argued that galaxies (then known as
spiral nebulae) were part of the Milky Way. Although he
lost the debate, his clear arguments won Shapley the
directorship of the Harvard College Observatory, a
position he occupied for more than three decades.
PORTRAIT: CHRISTIAN GALLET, COURTESY OF AIP EMILIO SEGRÈ VISUAL ARCHIVES, PHYSICS TODAY COLLECTION9
NOV. 8, 1656 –
JAN. 25, 1742
It’s been said that the general
public knows three astronomical
objects: the Moon, the rings of
Saturn, and Halley’s Comet.
English astronomer Edmond
Halley didn’t discover the object
named for him — he never even saw it — but his math-
ematical prediction of its return in 1758 guaranteed his
place in history.
Halley was a friend of Isaac Newton and used
Newton’s theory of gravity and to calculate “his” comet’s
orbit. In fact, Halley published at his own expense the
book Newton wrote explaining the theory, Philosophiæ
Naturalis Principia Mathematica.
In 1676, Halley sailed to the island of St. Helena in the
South Atlantic Ocean and spent a year measuring stellar
positions, the result of which was the first catalog of the
southern sky. PORTRAIT: PAUL MELLON FUND8
Edmond HalleyTOP: Edmond Halley never saw his eponymous comet, but in 1910,
Halley’s Comet came within 14 million miles (22 million km) of Earth,
allowing observers to take spectacular photographs — the first ever
taken of the comet. Its wispy tail is visible in this image, made with
an 8-inch telescope at Harvard College Observatory. DIGITAL ACCESS TO A SKY
CENTURY @HARVARD
BOTTOM: During the comet’s next pass in 1986, the European mission
Giotto took this image of the comet’s nucleus, revealing its rocky surface
and jets of dust and gas. HALLEY MULTICOLOR CAMERA TEAM, GIOTTO PROJECT, ESAOCT. 22, 1905 –
FEB. 14, 1950
American engineer Karl
Jansky was a pioneer of radio
astronomy. In 1931, using a large
antenna he had constructed,
Jansky discovered radio waves
that originated in the Milky
Way. Because this was a new branch of astronomy, other
scientists didn’t immediately follow up on his discovery.
Two that did, and who established the legitimacy of radio
astronomy, were Grote Reber of Wheaton, Illinois, and
John D. Kraus at the Ohio State University. Reber con-
ducted the first sky survey in radio wavelengths, while
Kraus invented many antennas that advanced radio
astronomy and wrote the most widely used textbook on
the subject. To honor Jansky’s original discovery, the unit
that astronomers use to measure the strength of a radio
source is named the jansky. PORTRAIT: NRAO/AUI/NSF10
Karl Guthe
Jansky
44 ASTRONOMY • FEBRUARY 2022