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I
n the early 1920s, American
astronomer Edwin Hubble
provided proof of the true
size of the universe. Working at
the Mount Wilson Observatory
near Pasadena, California, Hubble
used the newly constructed 100-in
(2.5-m) Hooker Telescope, at that
time the largest in the world,
to settle the greatest argument
then raging in astronomy. His
observations would lead to the
startling revelation that the
universe is not only far, far
larger than previously thought,
but is also expanding.Settling the Great Debate
At the time, the question of
whether spiral nebulae were
galaxies beyond the Milky Way
or a special kind of nebula was
the subject of a “Great Debate.”
In 1920, a meeting was held at
the Smithsonian Museum in
Washington, D.C., in an attempt to
settle the question. Speaking for
the “small universe” was Princeton
astronomer Harlow Shapley, who
contended that the Milky Way
comprised the entire universe.
Shapley cited as evidence reports
that the spiral nebulae wereBEYOND THE MILKY WAY
IN CONTEXT
KEY ASTRONOMER
Edwin Hubble (1889 –1953)BEFORE
1907 Henrietta Swan Leavitt
shows the link between period
and luminosity of Cepheid stars.1917 Vesto Slipher publishes
a table of 25 galactic redshifts.1924 Hubble shows that the
Andromeda galaxy lies well
outside the Milky Way.1927 Georges Lemaître
proposes that the universe
may be expanding.AFTER
1998 The Supernova Cosmology
Project and High-Z Supernova
Search prove that cosmos
expansion is accelerating.2001 Hubble Space Project
measures the Hubble Constant
(H 0 ) to within 10 percent.2015 The Planck Space
Observatory puts the age of the
universe at 13.799 billion years.rotating, reasoning that this must
make them relatively small because
otherwise the outer regions would
be spinning at speeds faster than
the speed of light (these reports
were later shown to be wrong).
Opposed to Shapley was Heber
D. Curtis, who supported the idea
that each nebula was far beyond
the Milky Way. Curtis cited as
evidence the discovery by Vesto
Slipher that light from most “spiral
nebula” galaxies was shifted to
the red part of the electromagnetic
spectrum, indicating that they
were moving away from EarthEdwin Hubble Born in 1889 in Missouri, Edwin
Hubble was a gifted athlete as
a youth, leading the University
of Chicago’s basketball team.
After graduating with a science
degree, he studied law at Oxford
University. Returning from
England dressed in a cape and
behaving like an aristocrat, he
was described by Harlow Shapley
as “absurdly vain and pompous.”
Despite his flair for self-
publicity, Hubble was a cautious
scientist. He described himself
as an observer, and reserved
judgment until he had sufficient
evidence. He reacted furiously ifanyone encroached on his field
of research. It is to Hubble’s
discredit, therefore, that he did
not acknowledge that 41 of the
46 redshifts used to formulate
his famous law were measured
not by him but by Vesto Slipher.
Hubble spent his last years
campaigning for a Nobel Prize
to be awarded in astronomy.
He died in 1953.Key work1929 A relationship between
distance and radial velocity
among extra-galactic nebulaeObservations indicate that
the universe is expanding
at an ever-increasing rate.
It will expand forever,
getting emptier and darker.
Stephen Hawking