THE SOUTHWORTH PLANETARIUM
207-780-4249   www.usm.maine.edu/planet
<http://www.google.com/url?q=http%3A%2F%2Fwww.usm.maine.edu%2Fplanet&sa=D&sntz=1&usg=AFQjCNHulkHuLP13bOG2PkNrPazsGWFs2A>
70 Falmouth Street   Portland, Maine 04103
43.6667° N                   70.2667° W
Altitude:  10 feet below sea level
Founded January 1970
Julian Date: 2458834.16
2019-2020:  LXXII
                 ""To confine our attention to terrestrial matters would be
to limit the human spirit."
                                      -Stephen Hawking

______________________________
Darn!
The lad who tamed Pegasus was named
Bellerophon, not Bellophon, as I wrote
in the Friday quiz.
I apologize for this error which, lamentably,
is not out of character.
Thanks to the DA subscriber who brought
this mistake to my attention.
______________________________


THE DAILY ASTRONOMER
Monday, December 16, 2019
Sun, No Sun


Ask us and we'll tell you with the sort of supreme self confidence borne of
knowledge that we won't ever be proven incorrect,  that the cosmos teems
with life. Life in unbounded abundance, assuming myriad forms all over the
Universe: from the microbes defiantly thriving in the volcanic calderas of
turbulent moons to the serene, cowl-covered, uber-evolved spirits
contemplating the infinite in deep caverns on barren ice planets.
Observations of Earth-bound beings has shown us life's mettle:  resiliency
that sustains it despite asteroid bombardments, climate catastrophes and
continent withering plagues.    Based on Earth alone, we can be well
assured that this Universe is tailor made for the optimists.   (Take heart,
pessimists.   I am sure one will find an occasional planet inhabited only
by beleaguered amoeba who spend their short lives looking frowningly up at
the incessant planetesimal bombardment.   "Wouldn't you know it, Bert, here
comes another growing shadow."   "Oh, I know."   BANG.)

Even the most life-happy astronomer, though, knows that life can only
emerge in certain places. We know that life forms cannot exist in regions
that are excessively hot or cold.   The chemical bonds within complex
molecules wouldn't survive high temperatures.  Conversely, metabolic
activity wouldn't persist in the deep cold.     For this reason,
astronomers have designated "goldilocks orbits," areas around stars where
temperatures might be conducive to life's development.  Neither too hot nor
too cold.

Another restriction pertains to the stars, themselves.       Not only would
a planet have to revolve within a specific orbit, the star would have to
persist long enough to allow evolution to work its magic: guiding life from
the primordial prokaryotic cell to the level of profound philosopher.
 Reviewing Earth's natural history suggests that evolution progresses so
slowly that a planet would need billions of years for intelligent life to
arise from the simple organic soup.*

How many stars would persist for billions of years.  Fortunately, most of
them!    A star's mass determines its life cycle. The least massive stars,
such as the red dwarf stars comprising about 70% of all the stars in the
galaxy, persist for billions of years.  The least massive of these could
remain active for more than a trillion years.  At the other end of the
spectrum, the most massive stars live only brief, at least by stellar
standards.    For instance, a star forty times more massive than the Sun
exists for only a million years:  hardly enough time to let an attendant
planet around such  a star to form a crust let alone a thriving
civilization.

So, we should qualify the phrase,  "stars are other Suns" because some of
the most massive and most luminous really won't be anybody's Sun at all.
   However, because these highly massive spheres represent a small fraction
of all the stars, we can say with confidence that most of the stars are
Suns. Consequently, we can expect a proliferation of life in the Milky Way,
a spiral galaxy in which starbirth is prodigious and gas stores from which
future stars will form is abundant.

It is little wonder we're so optimistic about life.



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*Yes, we know that Earth represents just one data point.  It is perfectly
possible that we're a slow-poke planet. Other planets could possibly have
formed shoppers and shoe makers out of the sea in far less time.