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
Julian date:  2457660.16
             "Go forth undaunted.  Yes, pretending to do so works, too."


THE DAILY ASTRONOMER
Wednesday, September 28, 2016
Cold Misconceptions


Bob and Phil retired a few years ago.  They were the highly agreeable, if
not particularly brain-burdened, pair who helped us address a variety of
astronomical misconceptions.     They are now in some remote paradise far
removed from the cares and trials of the everyday world.    We are still
seeking out their replacements, a task that has proven much more difficult
than we initially believed it would be.   While we scour the glacial plains
of the DA realm for two characters of equal amicability, we will look into
some common astronomical misconceptions ourselves.      Forgive  us if we,
unlike Bob and Phil, don't set our heads on fire, stuff ourselves in wells,
or plunge headlong into cloud forms in a desperate search for elusive
silver linings.      Instead, we'll proceed safely and prudently as we
tackle some common misconceptions.   Those that we'll address today are all
cold-weather related, as we are now moving through autumn en route to
winter and couldn't be happier.


*​The last touch of twilight illuminates an Arctic mountain range.   Image:
 Annette Mossbacher*

*1.   The North Pole is dark for six months of the year.*
If Earth had no atmosphere, the North Pole would go dark six months of the
year.  However, we do have an atmosphere, as evidenced by our ability
remain alive by breathing in it.     The atmosphere also scatters light and
make astronomy even more complicated.     The Sun rises at the North Pole
just before the vernal equinox and remains in the sky until just after the
autumnal equinox.  The Sun is just now setting at the North Pole.    For a
few weeks, the North Pole experiences perpetual civil twilight as the Sun
descends further below the horizon.  Civil twilight -which we call "dusk,"-
occurs when the Sun is below the horizon, but still within six degrees of
it.    Civil twilight at the North Pole won't end until mid October.
 Nautical twilight, when the Sun is more than six, but less than twelve
degrees of the horizon, is the period of time when the brightest stars
appear, but the horizon remains visible.  Nautical twilight won't end until
late October.  Astronomical twilight, when the Sun is more than twelve but
less than eighteen degrees of the horizon, follows nautical twilight won't
end until mid November.  However, one would be hard pressed to distinguish
between night and astronomical twilight.             Nautical twilight
begins at the North Pole around early to mid February and then civil
twilight starts in late Feb/early March.     So, the North Pole is truly
dark between Halloween and Valentine's Day.   A long night, indeed, but
certainly not six months in duration.