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
                            "Well, it's noon time somewhere..."




THE DAILY ASTRONOMER
Thursday, January 14, 2016
One Million Years

Let's imagine you live a million years.   Not technically immortal, of
course, but you'd certainly feel that way after attending your
great-great-great-great-great-great-great-great-great-great
grandhild's funeral.  Let's further pretend that during your prolonged
life span you retained an abiding love/obsession for astronomy.  You
wouldn't come to your senses about the oldest science even after
repeated exposures.    What would you experience that the rest of us
would not?



During your first few centuries, your experience and ours would be
quite similar. The sky would appear to turn about the spinning Earth;
and the constellations would abide by a consistent schedule.    You'd
have Orion the Hunter high in the south on a February evening; and the
Summer Triangle poised in the eastern evening summer sky.  The Sun
would rise due east and set due west on the equinoxes.  And, it would
be highest in the sky on the first day of summer; lowest on the winter
solstice.



Gradually, however, you would notice a slight shifting: a result of
precession, Earth's 'wobble,'  Over a 26,000 year period, Earth's
north pole describes a 47 degree circle along the night sky.
Consequently, the constellation positions change over time.   For
instance, the star Polaris (alpha Ursa Minoris) approximately marks
the North Celestial Pole.  In 2102, it reaches its least distance from
the NCP (27 arc minutes) before moving slowly away.     By 4,000 AD
the North Celestial Pole wanders through Cepheus the King; two
thousand years later, it's aligned with Cepheus' lower body;
Eventually, it moves through Cygnus the Swan and then by 13,000 it is
close to Vega, the summer triangle's brightest star.    Add a few more
thousand years, and the North Celestial Pole will run through Hercules
before migrating into Draco the Dragon.    The NCP was in Draco about
five thousand years ago, specifically by the star Thuban.    The
Egyptian pyramid builders likely looked toward Draco as the North Pole
constellation.    So, you would see the NCP turn in circles through
the sky.  26,000 years from now, it would be back close to Polaris.
Meanwhile, the constellations along the zodiac (ecliptic) move along
the path, so that Pisces, the current constellation hosting the vernal
equinox point (first day of spring) will be replaced by Aquarius in
2597 A,D, and then Capricornus in the 41st century.    Orion might
loom high in our winter sky now; but in 13,000 years, it would be high
and bright in the summer.  Of course, in another 13,000 years, it
would be back in the winter sky.



  During your million year life span, you'd witness this precessional
turnabout thirty eight times.   Of course, the constellations,
themselves, would experience profound changes in this time due to
proper motion: the movement of stars through the galaxy.   Though the
stars look stationary, they are traveling at rapid speeds around the
Milky Way's nucleus.    This alteration is painfully gradual and
today's star patterns would change imperceptibly even over thousands
of years.   However, during the first fifty thousand years of your
life, you would notice that the Big Dipper's bowl open and its end
handle star move away from the asterism's other stars, as though it
were melting.    Similarly, the Hyades star cluster comprising most of
Taurus the Bull's face, would appear to contract and move toward
Orion.  This motion results from its own  rapid recession from the
solar system.     Proper stellar motions will have transfigured all
the star patterns, so when you're lying on your death bed a million
years hence, all the present day constellations will be long gone.



So, too, will some of the presently prominent stars,   Betelgeuse and
Antares  are doomed to explode as supernovae.   Their imminent
detonations could happen soon, or might have already occurred and we
just haven't yet witrnessed their deaths.  Even if they remain intact,
these two red supergiants are not long for the galaxy. Before you're
100,000 years young (as you will call yourself), these two behemoths
will belong to the ages.    You'll also observe a fireworks display of
our supernovae throughout our part of the gakaxy over one million
years.  The Milky Way experiences about one supernova every 400 years
on average, although some of them will happen in such remote regions,
you'll be hard pressed to observe it.



Throughout your million years of milling about, the day length will be
17 seconds longer and the Moon's mean distance will have increased by
approximately 36 miles.  The increase in both day length and lunar
distance are directly related.  The Moon recedes from us slowly and
this recession impedes Earth's rotation.     Neither effect will
profoundly affect (ha ha, high school English teachers) your life.
You'll still have ample opportunity to observe solar eclipses.  -Those
won't stop for at least 600 million years-.   While it is highly
unlikely that our calendar will persist throughout your life, if it
did, the 17 extra seconds would prove problematic as they would add
1.7 hours to each year.  That extra time can accumulate quickly,
Julius.



However, though your life might seem interminable to you and to your
1,867th spouse, one million years still constitutes a meager fraction
of time by cosmic standards.     During those million years, your home
solar system will have only completed 1.6 degrees of its entire
circuit around the galaxy.    The Andromeda and Milky Way Galaxies,
both destined to collide in 5 billion years, will be 0.02% closer to
each other at the end of your life as they are now.   Planets will
continue to inexorably orbit stars that are prodigiously generating
energy.  This energy dissipates through a rapidly expanding cosmos
that will seem more or less the same in a million years as it does
now.



Astronomy teaches us that so much more is destined to transpire
through a Universe that will remain as furiously energetic as it is
fiercely creative for billions of years to come.      Makes you want
to eat that second piece of cake, doesn't it?