The Sloan telescope is about 100 miles from the nearest
big city, El Paso, atop a paradise of soaring ponderosa
pines and Douglas firs. It is located atop the mountain
which overlooks Alamogorgo, New Mexico, and can be seen
from most places in the city.
The Sacramento Mountains rise like brilliant green drapery
of the New Mexican desert. Below, a desert expanse as
large as Massachusetts stretches to the horizon. On one
side is the White Sands Missile Range; on the other, the
city of Alamogordo. At night, a deep blackness descends.
The Sloan Digital Sky Survey (SDSS) is one of the most
ambitious and influential surveys in the history
of astronomy. Over eight years of operations (SDSS-I,
2000-2005; SDSS-II, 2005-2008), it obtained deep, multi-color
images covering more than a quarter of the sky and created
3-dimensional maps containing more than 930,000 galaxies and
more than 120,000 quasars. SDSS data have been released to
the scientific community and the general public in annual
increments, with the final public data release from SDSS-II
scheduled for October 31, 2008. SDSS-III, a program of four
new surveys using SDSS facilities, began observations in
July 2008, and will continue through 2014.
The SDSS used a dedicated 2.5-meter telescope at Apache
Point Observatory, New Mexico, equipped with two powerful
special-purpose instruments. The 120-megapixel camera imaged
1.5 square degrees of sky at a time, about eight times the
area of the full moon. A pair of spectrographs fed by optical
fibers measured spectra of (and hence distances to) more
than 600 galaxies and quasars in a single observation. A
custom-designed set of software pipelines kept pace with
the enormous data flow from the telescope.
During its first phase of operations, 2000-2005, the
SDSS imaged more than 8,000 square degrees of the sky in
five optical bandpasses, and it obtained spectra of
galaxies and quasars selected from 5,700 square degrees of
that imaging. It also obtained repeated imaging (roughly
30 scans) of a 300 square degree stripe in the southern
Galactic cap.
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This is the bottom of the 2.5-meter survey telescope,
where the instrument package(either mosaic camera or
spectrograph) is mounted.
Looking inside the base of the 2.5-meter survey telescope.
The stack of rings sits just above the primary mirror and
serves to shield the instruments below from stray light.
The telescope enclosure building (above) and instrument
room (below) jut out from the mountainside. The SDSS
telescope facility was designed this way to provide
the calmest and coldest possible air above and around
the survey telescope.
A look down inside the 2.5-meter survey telescope reveals
the primary mirror(the reflective surface at the bottom)
as well as the secondary mirror (center), all surrounded
by the wind baffle.
The 2.5-meter diameter primary mirror of the SDSS
telescope. This photo was taken with the telescope
horizontally on its side, pointing into the trees.
The SDSS 2.5-meter telescope.
Apache Point Observatory in the Sacramento Mountains of
New Mexico. The Sloan Digital Sky Survey's 2.5-meter
telescope is on the left. White Sands National Monument is
visible in the distance, above the telescope. The monitor
telescope, used for calibrations, is inside the small
dome to the right of center. Optical fibers for
spectroscopy are pre-positioned each day in the building
on the right (behind the trees). The building in the
center rolls on rails to cover the 2.5-meter telescope
when i t is not in use.
The secondary mirror of the 2.5-meter telescope.
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