THE SOUTHWORTH PLANETARIUM
207-780-4249       www.usm.maine.edu/planet
70 Falmouth Street  Portland, Maine 04103
43.6667° N,                    70.2667° W
Founded January 1970
                    "On the best cellars list."


THE DAILY ASTRONOMER
Thursday, March 3, 2016
Queen of the Road

Circumpolarity is a funny thing.
First, there's the word itself that, when spoken, seems circular, as
though the syllables arrange themselves along a closed curve.
Cirumpolarity, incidentally,  refers to those stars and constellations
that never set; well, at least not in our lifetimes.   The Big and
Little Dippers are the most famous circumpolar patterns.  -We can't
call them constellations because they are asterisms, defined as star
patterns within constellations.*

Secondly, the circumpolarity concept often proves troublesome to sky
watchers because not all stars are circumpolar, unless you're a South
Pole or North Pole observer.     Determining which stars never descend
below the horizons can prove a bit tricky.  Here, in these balmy
climes, the circumpolar stars are those clustered around the North
Celestial Pole, the position of which Polaris, the North Star,
approximates.     The six wholly circumpolar constellations -as
opposed to those only partially composed of circumpolar stars- are
Ursa Major, Ursa Minor, Camelopardalis the Giraffe, Draco the Dragon,
Cepheus the King and Cassiopeia the Queen.   A select group amongst
the more than fifty constellations visible from this latitude.

The third problematic matter pertaining to circumpolar is visibility.
Sometimes a circumpolar constellation is quite difficult to find when
it lingers around its low point.    All the circumpolars appear to
travel along circular orbits centered on the North Celestial Pole.
This circle expands with increasing distance from the pole.  The stars
close to Polaris describe small circles; those farther away, such as
in the Big Dipper and Cassiopeia, follow much longer paths; paths that
bring them close to the horizon and then almost directly overhead.

Curiously, the Big Dipper and Cassiopeia occupy opposite points
relative to Polaris.  So, when one ascends toward the zenith, the
other descends toward the horizon.   Throughout late autumn and most
of the winter, the Big Dipper begins the evening either resting on the
horizon or low in the northeast.  Conversely, Cassiopeia looms high
overhead.         Now that we're steaming toward spring with
sloth-like fury, Cassiopeia's evening position is lower while the Big
Dipper rises.    By late evening (just before midnight), if one is
hiking merrily across the glacial expanses of this heaven-forsaken
wasteland because one has no other means of coping with a mid-life
crises and damn it all to hell, I'm stupid,  one will observe
Cassiopeia on the road.  Well, she'll appear to be lurking in the
distant realm where the road boundaries appear to converge toward an
unattainable point.

Circumpolar Cassiopeia prepares for her warm weather repose while the
great bear Ursa Major (Big Dipper) rises out of its hibernation
dwelling.    A sign -the only one- that the frigid season is destined
for a much anticipated end.




*The Little Dipper is part of Ursa Minor (the Minor Bear)  the Big
Dipper is in Ursa Major (the Great Bear.)