Sky & Telescope - January 2022 - 26

Treasures in the Sky
SEEING NUMBERS To many observers
the first sight of NGC 2169 in the eyepiece
often elicits a chuckle or two.
10 A Frozen Toe. For many of us, the sky lore we're most
familiar with largely consists of stars with Arabic names that
reside in the characters of Greek mythology. It's fun, however,
to explore the vision of the sky expressed in other cultures. In
Norse legend, the star Rigel (Beta Orionis) represents the big
toe of Orwandil (Orion), who got frostbite while crossing a
river. Thor, Orwandil's traveling companion, snapped off the
frozen digit and hurled it into the sky. In some versions of the
myth, the severed toe became the star Alcor (Mizar's fainter
companion in the Big Dipper), while Rigel represents the
remaining big toe. Rigel is a blue supergiant around 60,000
times more luminous than the Sun (with some estimates
leaning toward even greater figures). Hiding in the glow of
this brilliant, magnitude-0.3 star at a separation of a bit more
than 9″ is a tiny, 6.8-magnitude companion - the view in
a 10-inch scope makes for a spectacular contrast with the
bright, white primary. The secondary is itself a binary comprising
two main sequence stars that are too close to split.
The pair orbits Rigel at a distance of about 2,000 a.u. Spectroscopic
observations suggest that a fourth star might belong to
the Rigel system as well.
11 A Triple Wonder. William Herschel described Beta
Monocerotis as " one of the most beautiful sights in the
heavens. " Today, many call it Herschel's Wonder Star. This
lovely system consists of three nearly equal-magnitude white
stars. The primary is magnitude 4.6 and is separated by about
7″ from a very close pair of nearly identical beauties of magnitudes
5.0 and 5.3. Use at least a 4-inch scope to enjoy this
26 JANUARY 2022 * SKY & TELESCOPE
sight. Beta Monocerotis represents a hoof of the Unicorn and
is the brightest object between Sirius and Betelgeuse.
12 An Orbuculum. This obscure word is another name
for a crystal ball, which is the nickname given to NGC 1514
in Taurus. The planetary nebula, with its bright central
star surrounded by a translucent spherical shell, is indeed
reminiscent of a crystal ball. And somewhat like the sphere
fortunetellers employ, it also has a way of foretelling the
future - specifically, it might divine the future quality of
your observing night by how well this mercurial orb shows
up without a filter. If you can detect the planetary's faint disk
without a filter, you can grade the night's transparency as
excellent. On less-than-perfect nights, you'll need a narrowband
filter to observe the disk.
13 A Capricious Demon. Rounding out this baker's dozen
of celestial gems is the most famous variable star in the sky.
Algol (Beta Persei) is an eclipsing variable and the first of its
kind ever discovered. The hero, Perseus, is depicted as carrying
the severed head of the Medusa, a mythical snake-haired
monster. Algol represents that head and so earned its nickname
the Demon Star. It's a triple-star system, with the inner
close binary responsible for the object's periodic dimming.
Fainter Algol B eclipses brighter Algol A every 2.87 days, dropping
the magnitude from 2.1 to a minimum of 3.4, where it
stays for about two hours before brightening again. The difference
between the maxima and the minima are plainly visible
to the naked eye. The star is usually equal in brightness to
TENHO TUOMI
Sky & Telescope - January 2022

Table of Contents for the Digital Edition of Sky & Telescope - January 2022
