My first Magazine Sky & Telescope - 03.2019 | Page 16

FAMOUS STARS, PART I
by Camille M. Carlisle
of
The North Star presents a façade of constancy,
but it hides a capricious temperament.
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M A RCH 2 019 • SK Y & TELESCOPE
p FINDING THE NORTH STAR A stargazer demonstrates how to fi nd
Polaris: Follow the pointer stars at the end of the Big Dipper’s bowl and
extend the line between them about 5 times. The man’s left hand points
to Merak in Ursa Major, his right to Polaris.
The Pole Star
Polaris (Alpha Ursae Minoris) is a fat, bright, and aging yel-
low star. If you could put Polaris and the Sun side by side,
Polaris would be 2,000 times brighter. It’s roughly 45 times
wider than our star, too, and if placed at the center of our
solar system, its surface would reach more than halfway to
the orbit of Mercury.
Alpha UMi sits less than a degree from the north celes-
tial pole, the point on the sky that you’d hit if you extended
I
t’s arguably the most famous star in the sky — although
more people have trouble fi nding it than would care to
admit it. And truth be told, when it comes to the bright-
est stars, the 2nd-magnitude supergiant has nearly 50 stars
ahead of it in line. But Polaris has been a guiding light for
generations of seafarers and star-party goers alike, a haven of
stability in a sky that whirls around it every night.
That stability is short-lived, however. Polaris has only
reigned on its celestial throne for the last millennium, and in
less than a century it will begin its abdication. Nor is the star
itself stable: It wobbles in position as two companions waltz
with it through space, and its light brightens and fades in a
predictable pattern — except when it doesn’t. In short, there
is almost nothing constant about the North Star.