The best 3-D map of the cosmos just got better, thanks to
an astronomer's years of cleaning up old satellite data.
The fresh look at almost 118,000 stellar bodies, known as
the Hipparcos catalogue, boosts the astrometric database's accuracy by up to
five times and effectively doubles its useful information.
"This catalogue provides extremely fundamental,
direct measurements in astronomy, such as distances, masses and kinematics of
stars and star clusters," said Floor van Leeuwen, an astronomer at the Institute of Astronomy at University of Cambridge in the U.K. who single-handedly filtered the data.
Van Leeuwen's updated version of the catalogue is
detailed in part of a new book called "Hipparcos - The New Reduction of
the Raw Data."
Star-crossed satellite
In 1989,
the European Space Agency (ESA) launched Hipparcos—the High Precision Parallax
Collecting Satellite—to map out some of the brightest stars and star clusters
in the cosmos.
Van Leeuwen
said the satellite's data may be old, but its accuracy is still impressive.
"If the satellite was on Earth, it would be able to see a child on the
moon take a step," van Leeuwen told SPACE.com.
The
satellite scanned the sky in two directions for 4 years, allowing astronomers to
calculate the distance
from Earth to each stellar object by using the parallax method-or observing
an object from two points in space, when Earth is in different points on its
orbit around the sun. Our brains, for example, use the same principle to merge
information from two eyes to give us depth perception.
"You're
essentially triangulating the entire sky," he said of computing Hipparcos'
data. Complicating the extremely precise calculations, however, was the
satellite's off-kilter orbit around Earth caused by a failed rocket.
Van Leeuwen
said comparing both data sets amounts to a dizzying amount
processing—especially with errors
present.
Nasty
number crunching
Red flags
in the catalogue-such as a 10 percent difference in calculated distance to the
Pleiades star cluster-set astronomers off to the errors, but they struggled to
understand them. Scientists eventually showed that fast-moving dust grains
whacking into the spacecraft could vibrate it and throw off measurements.
"Pings" in satellite material caused by solar heating and
contraction, similar to the sounds made by a cooling car engine, were also isolated.
With the
information in hand, van Leeuwen decided to sit down at his computer and
painstakingly filter through the 118,000 data points, then re-crunch the
numbers.
"It
took me about two-and-a-half years in total, and I found about 1,600 of these
events," he said. "When I took the events out of the data, the
accuracy increased by a factor of five."
Van Leeuwen
said his personal computer took about three to four weeks to process one
iteration, or "rough draft," of the cleaned-up stellar map-and 15
total iterations were needed to create the complete final draft. But the new
version, he said, should help astronomers better understand the motions of the
cosmos as well as inform the design
of Gaia-the next-generation astrometric satellite.
The ESA
expects Gaia to observe about 1 billion stellar objects, or about 8,300 times
more than Hipparcos did in the early 1990s.
"It's
absolutely frightening to think about the data that will be coming down from
Gaia," van Leeuwen said of the satellite, which is scheduled to launch in
2011. "The world's best computers currently can't handle that kind of
data, so we hope we'll be able to in about 5 years' time."
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