274
GALAXIES APPEAR TO
E ON THE SURFACES OF B
BUBBLELIKE STRUCTURES
REDSHIFT SURVEYS
IN CONTEXT
KEY ASTRONOMERS
Margaret Geller (1947–)
John Huchra (1948–2010)BEFORE
1842 Christian Doppler
describes how wavelengths can
change due to relative motion.1912 Vesto Slipher discovers
that galaxies are redshifted
by the Doppler effect.1929 Edwin Hubble uses
redshift to show that distant
galaxies are moving away
faster than nearer ones.1980 Alan Guth proposes that a
rapid expansion, called cosmic
inflation, shaped the universe.AFTER
1998 The Sloan Digital Sky
Survey finds walls, galaxy
sheets, and filaments many
hundreds of light-years long.1999 A redshift survey of
supernovae reveals that the
universe’s expansion is
speeding up.S
ince the 1920s, the study
of the redshift of distant
galaxies has revealed the
scale of space and the way in
which the universe is expanding
in all directions. Redshift occurs
when a light source is moving away
from the observer (p.159). In the
1980s, redshift surveys made by
American astronomers Margaret
Geller and John Huchra, working
at the Harvard–Smithsonian Center
for Astrophysics (CfA), gave an
even clearer picture of the universe,
showing that galaxies cluster
around great voids of emptyMargaret Geller Margaret Geller earned a Ph.D.
from Princeton in 1975, and
took various fellowships before
joining the Harvard–Smithsonian
Center for Astrophysics in 1983.
She worked there with John
Huchra, analyzing the results of
his redshift survey. Geller went
on to lead the second (CfA2)
redshift survey. She is a frequent
public speaker and has made
several films about the universe,
including Where the Galaxies
Are, which takes viewers on
a graphical voyage around
the large-scale objects of the
observed universe.space. Geller and Huchra’s work
provided valuable clues to the
nature of the very early universe.
A redshift survey uses a wide-
angle telescope to select target
galaxies, generally millions of
light-years away. Astronomers
compare the light from each galaxy
with benchmark wavelengths to
determine the redshift, and thus
the distance the light has traveled,
allowing them to plot the positions
of many galaxies. Huchra started
the first redshift survey in 1977;
by its completion in 1982, he had
mapped 2,200 galaxies.