296
See also: Beyond the Milky Way 172–77 ■ Quasars and black holes 218–21 ■
Studying distant stars 304–05 ■ Looking farther into space 326–27S
et up to produce “a field
guide to the heavens,” the
Sloan Digital Sky Survey
(SDSS) began operating in 1998.
The ambitious goal was to make
a map of the universe on an
immense scale—not just a survey
of objects on a celestial sphere,
but a three-dimensional model of
a large portion of deep space. The
project was initially headed by US
astronomer Donald York, but is
now a collaboration between 300
astronomers from 25 institutions.
SDSS uses an 8-ft 3-in (2.5-m)
telescope at Apache Point, New
Mexico. The telescope’s wide-angle
camera has digitized objects visible
from the northern hemisphere.
From the 500 million objects
visible, the brightest 800,000
galaxies and 100,000 quasars
were selected, and their sizes
and positions in the sky accurately
transposed as holes drilled into
hundreds of aluminum disks. When
fitted to the telescope, a disk blocks
unwanted light, and feeds the light
from each target galaxy into its
own dedicated optical fiber andonto a spectroscope. From
these accurate galactic spectra,
the astronomers can figure out
how far away each galaxy is. Data
collection began in 2000 and is
expected to continue until 2020.
The information gathered so far
has revealed galaxies in clusters
and superclusters, and even galactic
“walls”—immense structures
containing millions of galaxies,
forming a tangled cosmic web
with vast voids in between. ■THE MOST AMBITIOUS
MAP OF THE
UNIVERSE EVER
A DIGITAL VIEW OF THE SKIES
IN CONTEXT
KEY ASTRONOMER
Donald York (194 4 –)BEFORE
1929 Edwin Hubble proves
that the universe is expanding.1963 Maarten Schmidt
discovers quasi-stellar objects,
or quasars, which turn out to
be young galaxies.1999 Saul Perlmutter, Brian
Schmidt, and Adam Riess
show that the expansion of
the universe is increasing
due to the mysterious effects
of “dark energy.”AFTER
2004 Construction begins
on the James Webb Space
Telescope, which will use
infrared to see the first stars
that formed after the Big Bang.
2014 Approval is given for
the European Extremely Large
Telescope, which will have a
128-ft (39-m) segmented main
mirror, making it the most
sensitive optical telescope ever.A cube section of the SDSS sky map
shows the intricate distribution of
matter in space. The tangles of light
are interconnected galaxies.