THE 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: 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.