My first Magazine Sky & Telescope - 03.2019 | Page 28

STAR SLEUTHING by Guillermo Abramson
ow far away are the stars? You might think that
astronomers should know, but distances to the stars
are something very diffi cult to fi gure out. In daily
life, we estimate nearby distances using a trigonometric
trick built into our bodies: Our eyes see the world from two
slightly different perspectives, and our brain processes this
difference to build a three-dimensional image of our envi-
ronment. This shift in an object’s apparent position, called
parallax, enables us to complete a myriad of tasks, from
threading a needle to catching a ball in mid-air.
Since classical antiquity astronomers have labored to use
the same method on the stars, by observing the apparent
H
shift of the position of a star while the Earth moves along
its orbit. But the stars are so far away that it was only in the
19th century that astronomers fi nally succeeded in measur-
ing a handful of stellar parallaxes. Measurements on a grand
scale had to wait for modern technology.
Near the end of the 20th century, the European Space
Agency (ESA) designed a space telescope to measure stellar
parallaxes. The High Precision Parallax Collecting Satel-
lite (Hipparcos, named in honor of the Greek astronomer
Hipparchus of Nicaea from the 2nd century BC), observed a
predefi ned set of stars over four years. The result was the Hip-
parcos Catalogue, published in 1997 and containing precise
PLACING
the Pleiades
The second data release from the Gaia mission
solves a decades-long controversy about the
distance to the Pleiades cluster.
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M A RCH 2 019 • SK Y & TELESCOPE