Sky and Telescope - January 2017 - 10

NEWS NOTES

MISSIONS

THE EUROPEAN Space Agency (ESA)

has released the long-awaited ﬁrst
results from its Gaia mission, which
is mapping the locations of 1.1 billion
stars across the Milky Way and beyond.
This ﬁrst version of Gaia's atlas gives
positions on the sky for those stars to a
precision of less than a microarcsecond
for suns as faint as magnitude 20.7.
That's equivalent to pinpointing the
exact location of a sand grain in San
Francisco as seen from Boston. Never
before have astronomers measured the
locations of such a quantity of stars to
such high precision.
Gaia hovers at the L 2 Lagrangian
point, a gravitational "neutral zone"
about 1.5 million km (1 million miles)
from Earth's nightside that moves
with our planet as it orbits the Sun.
The mission's main goal is to create an
extraordinarily precise, 3D star map.
To do this, the spacecraft will monitor each star about 70 times over a
ﬁve-year period as it scans the sky. It's
looking for stellar parallax, the tiny
10

J A N U A R Y 2 0 1 7 * SK Y & TELESCOPE

apparent annual looping in a star's
position caused by the spacecraft's
moving viewpoint as it travels with
Earth around the Sun.
The catalog's visual representation
(above) is an all-sky map with a spatial
resolution comparable to that of the
Hubble Space Telescope. "It's like taking
a Hubble image - just of the entire sky,"
explains team member Anthony Brown
(Leiden University, The Netherlands).
In addition, the atlas includes measurements of 599 Cepheid stars (43
newly discovered) and 2,595 RR Lyrae
stars (343 new) around the south ecliptic pole. These variable stars are vital to
calculating the cosmic distance scale.
For a subset of 2 million stars,
scientists have already combined Gaia
data with older measurements from the
Hipparcos mission to estimate distances
and motions. But this ﬁrst Gaia release
only includes observations from the
ﬁrst 14 months of operations and does

p This all-sky view from ESA's Gaia mission
shows stars in the Milky Way and in neighboring
galaxies, including the Magellanic Clouds (lower
right). The map's resolution enables astronomers to study individual stars in these galaxies.
Stripes are artifacts due to Gaia's scanning
procedure and will disappear as more data are
gathered. Background color comes from a Gaia
visualization of stellar density across the sky.

not include parallaxes for all 1.1 billion
stars - those will come later. Scientists will issue additional, intermediate
results as the mission progresses. The
ﬁnal batch of data is expected in 2023,
about three years after the space mission has ended.
Gaia data are public, and ESA has
released both the raw data and a 3D
visualization software called Gaia Sky
for those who want to explore.
■ JAN HATTENBACH
Further Reading:
Find weblinks to access Gaia's ﬁrst data
dump and other materials in the extended
version of this story online: https://is.gd/
gaiarelease1.

* To get astronomy news as it breaks, visit skypub.com/newsblog.

ESA / G AIA / DPAC, BACKG ROUND A LL-SK Y: ESA / G AIA / CC BY-SA 3.0 IGO

Gaia Maps a 1,000,000,000+ Stars

https://www.is.gd/gaiarelease1 https://www.is.gd/gaiarelease1 http://www.skypub.com/newsblog

Sky and Telescope - January 2017

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