Sky & Telescope - September 2016 - 14

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Cosmic Flood

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PETER TYSON

How will astronomers cope with
the tsunamis of raw data soon to
pour in from wide-field surveys?
Not long ago Henry "Trae" Winter, an astrophysicist at
the Harvard-Smithsonian Center for Astrophysics, gave
a talk entitled "Big Data to Big Art." Winter works on
NASA's Solar Dynamics Observatory mission, and he
wanted to give his audience an idea of just how much
image data the SDO's telescope generated each day. The
scope's four cameras take pictures of our star every 12
seconds in eight different wavelengths, which results in
3 terabytes' worth of images each day.
How much is that exactly? Winter made an analogy
with Blu-ray discs. A standard, dual-layer Blu-ray holds
about 50 gigabytes of data, so in one day SDO generates
60 Blu-rays' worth of data. The mission has been running for six years - 131,400 Blu-rays - and the team
hopes to observe the Sun's entire 11-year cycle. Imagine
trying to watch all those discs, deleted scenes and all.
The same thing is happening all over astronomy. And
today's "big data" pales next to what's coming, both with
surveys already underway, such as the Panoramic Survey
Telescope and Rapid Response System (Pan-STARRS)
and with those in development, including the Large Synoptic Survey Telescope (LSST) and the Square Kilometer
Array. These and other visual and radio telescopes will
blow SDO out of the sky in terms of data output.
To explore what big data means in the astronomy context, and to look at the challenges it presents, let's take a
close look at the principal U.S. project being developed
in ground-based astronomy for the 2020s: the LSST.
14

September 2016 sky & telescope

A Data Tsunami
The LSST is currently under construction near La
Serena, Chile. When completed, it will share a ridge
on Cerro Pachón with the Gemini South and Southern
Astrophysical Research telescopes. Its chief funders are
the U.S. National Science Foundation (for its facility and
telescope), the U.S. Department of Energy (its camera),
and various philanthropists (its mirror). This year alone
LSST will consume about $140 million, with an estimated $1 billion over its lifetime.
The LSST will have three components: an 8-meter
wide-field telescope, a 3.2-billion-pixel camera, and an
a
automated data-processing system. The scope's field of
view will be much larger than that of any other
oth 8-meter
telescope: 3.5°° degrees, or about seven tim
times the diameter of the full Moon. Every 40 seconds or
o so the telescope
will point to a new area of the sky, and its camera will
take two 15-second exposures (to efficiently reject cosmic
rays). The camera will record using six different visual
and near-infrared fi lters, and over its anticipated 10-year
run it will capture some 40 billion objects in an unprecedentedly large volume of the universe.
un
Besides being wide, fast, and deep, LSST will add
the time domain. After those 10 yyears, this will result
in a sort of stop-motion movie o
of much of the celestial
sphere. All told, the camera will image about 10,000
square degrees of sky every three clear nights. LSST will
not stop for follow-up observations
observation but will simply keep
harvesting night after night.
LSST leaders expect astronomers to use the output
from this technological juggernaut to explore many
key science areas. Four in particular will
w be counting
asteroids and other moving objects in our
ou solar system,
mapping the structure and evolution of the Milky Way,
exploring transient phenomena such as supe
supernovae and
other variable stars, and constraining the nature of dark
energy and dark matter. But the science will be up to the
scientific community. LSST will simply collect the data
- a continuous tsunami of it.
The project expects to accumulate 15 terabytes of raw
data each night - five times what SDO garners daily.
Fifteen terabytes a night is a lot, but within a few years,
the cumulative data will become petabytes in size. (A
petabyte is 1,000 terabytes; see the table above right.)
"That's a scale we're not typically used to," says Andrew



Sky & Telescope - September 2016

Table of Contents for the Digital Edition of Sky & Telescope - September 2016

 Contents
Sky & Telescope - September 2016 - Cover1
Sky & Telescope - September 2016 - Cover2
Sky & Telescope - September 2016 - 1
Sky & Telescope - September 2016 -  Contents
Sky & Telescope - September 2016 - 3
Sky & Telescope - September 2016 - A
Sky & Telescope - September 2016 - B
Sky & Telescope - September 2016 - 4
Sky & Telescope - September 2016 - 5
Sky & Telescope - September 2016 - 6
Sky & Telescope - September 2016 - 7
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