THE USM SOUTHWORTH PLANETARIUM

207-780-4249     www.usm.maine.edu/planet

70 Falmouth Street     Portland, Maine  04103

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.

(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.