THE USM SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
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70 Falmouth Street Portland, Maine 04103
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43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian date: 2458694.5
"Just another day in deep space...."
THE DAILY ASTRONOMER
Monday, July 29, 2019
The Winter Hexagon's Cap
is visible this evening, if one knows where to look.
[image: Winter-Hexagon.jpg]
(Yes, we're just as surprised as you are to read that sentence.)
That one can observe the Winter's Hexagon's northernmost star in late
July illustrates
two principles: one, that astronomers should be more careful assigning
names to star patterns, and, two, that the wholly predictable night sky is
not without its surprises.
For those who might have forgotten, the Winter Hexagon is a vast
oval-shaped pattern consisting of stars from different constellations.
Starting from the southernmost point, these Winter Hexagon points are
Sirius (Canis Major), Rigel (Orion), Aldebaran (Taurus), Capella (Auriga),
Castor and Pollux (Gemini) and Procyon (Canis Minor.) Some astronomers
also include Betelgeuse (Orion), positioned almost dead center within the
hexagon. Other uncooperative astronomers don't add Betelegeuse as it
doesn't contribute to the Hexagon's boundaries.
The Winter Hexagon is conspicuously absent from the evening sky now, but
give us six months, when we're facing a different part of the galaxy, and
one will see this brilliant stellar conglomeration front and center in the
evening sky. We call it the "Winter Hexagon" because it is easy to see in
the winter. Presently, most of its stars are only now just rising in the
pre-dawn eastern sky. One star, its northernmost member, Capella,*
lingers almost ominously in the northeastern mid evening sky. It is
THAT strange bright star that just hangs above the northern horizon when
everybody's attention is focused on the Summer Triangle, Sagittarius and
the other summer sky adornments. Despite lurking low along the nether
edge, Capella is still easy to spot, as it is the night sky's sixth
brightest star.
Apart from this distinction, Capella is also a "Vegan star," defined as a
star that is visible for at least part of the night every night of the
year. Pronounced "Vay gan," Vegan stars are hybrids: not high enough to
be circumpolars -stars that never set- but high enough to make an
appearance on stage each night. These stars are named for Vega, the
brightest star in the Summer Triangle. It, too, is visible for at least
part of the night each year.**
It is easy to forget that the Universe is a show on a half shell: that the
center stage performers in the south comprise only a small part of the
entire ensemble. If you're pining for winter and yearn for its return,
we'll cheerfully inform you that we can do nothing to hasten its arrival.
Instead, we can point you to the secret northern sky corner, where Capella,
the Winter Hexagon's highest star, meanders quietly along, waiting for the
deep winter chill to return.
Hmm... can't wait.
*Remembering that Capella sits atop the Winter Hexagon is easy: just think
of it as the Winter Hexagon's "cap."
**Vega and Deneb, the Summer Triangle's other northern star, are both Vegan
stars. For instance, one can find them both peeking above the northern
horizon on an early evening in February. They set by mid evening, only to
rise again well after midnight. They are the stars that console the
summer lovers as they languish through winter.