Johns Hopkins Gazette: October 24, 1994

Hopkins Astronomers to Lead Search for Structure of Universe
By Emil Venere

A new telescope aimed at answering one of the most
fundamental questions in cosmology is being developed by
scientists at Hopkins and beyond.
    Now the quest for discovering the structure of the
universe has received a financial boost. The National
Science Foundation last month awarded a $5 million grant to
the Sloan Digital Sky Survey, which involves scientists from
Hopkins and other institutions in the United States and
    "The Sloan project is arguably the most exciting of the
currently planned long-term projects in ground-based
astronomy," said Alexander Szalay, a Hopkins professor of
physics and astronomy who leads the team of scientists
working on software for the project. "About two or three
months into the project we will have more data than all
astronomy had before."
    The survey, which is expected to take about five years
to complete, will dramatically increase knowledge about
galaxies. The best sky surveys now contain 2 million
galaxies, but astronomers have reliable distance
measurements for as few as 20,000 galaxies.
    The observatory, under construction in south-central
New Mexico, may enable astronomers to survey 100 million
galaxies and stars, some as far as 3 billion light-years
away. Then, astronomers plan to concentrate on the brightest
1 million galaxies, studying details about their distance,
age and composition, Dr. Szalay said. 
    Hopkins scientists will design and build the
telescope's spectrograph, an instrument that will enable
astronomers to study about 100,000 quasars, or quasi-stellar
radio sources, distant objects that look like stars when
viewed through conventional telescopes but are actually
hundreds of times brighter than an entire galaxy. 
    "The idea is that we are going to pick up a lot of
quasars in the process, which will give us another view of
the structure of the universe," said Hopkins research
scientist Alan Uomoto, project scientist for the team that
is designing and building the spectrograph. "This is the
first time that a large group of ground-based astronomers
has gotten together to solve a particular research problem,
and not just build a large instrument for general use."
    The challenge is determining the large-scale structure
of the universe. By mapping the cosmos in detail,
astronomers will learn how galaxies are organized into
clusters and "superclusters," which ultimately will help
cosmologists understand more about the processes leading to
the present structure of the universe.
    Construction on the observatory began in the summer of
1993, with initial funding of $8 million from the Alfred P.
Sloan Foundation. Scientists expect to begin testing the
telescope within a year and have it fully operational in
about two years. It is located at Apache Point, near
Sunspot, N.M.
    The telescope will be extremely sensitive to distant
light because its focal plane will be lined with
charge-coupled devices, light-sensor chips used in video
cameras that enable scientists to capture an image
accurately. The typical large telescope has one CCD in its
focal plane, but the Sloan  telescope will contain 54 of the
devices, 30 in the focal plane.
    The survey will cover half of the northern sky--or a
quarter of the total sky--since the other half is obscured
by the bright, nearby plane of the Earth's galaxy.
    Another major part of the project will be to make the
volumes of information available to scientists and
nonscientists. Over five years researchers will collect up
to 20 trillion bytes of data, or roughly enough information
to fill 10 million floppy disks. Just one night of
observations will provide enough information to fill a few
thousand floppy disks, Dr. Szalay said.
    Most of the sky survey information will be placed in a
digital archive, probably in the form of compact discs,
which will be made available to the public. It will be the
first extensive collection of astronomical data recorded
originally on computer. Many other sets of data in existing
archives have been converted from original photographs into
digital form for computer storage, reducing the clarity of
the images.
    Researchers from the Physics and Astron-omy Department
and the Computer Science  Department are creating the
archive software.
    The project is being managed by the nonprofit
Astrophysical Research Consortium, whose members include
Hopkins and several other institutions involved in the
survey: Princeton University, the Institute for Advanced
Study, the University of Chicago and the University of
Washington. Also involved in the project are Fermi National
Accelerator Laboratory, the Naval Research Observatory and a
group of Japanese astronomers.

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