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

             "In the popular belief, most astronomers end by losing their minds."

                            -H.L. Mencken (1880-1956)




THE DAILY ASTRONOMER
Thursday, May 5, 2016
Weather vs. Astronomy


We did promise to address at least two Pandora inquiries each week.   Yesterday, we only answered one, as the response was quite involved.    Since tomorrow we have our weekly quiz, today is the only time when we can answer the second question this week.       Now, one might think that we just wrote this question under an assumed name for purposes of self-flattery, but we assure you this query came to us from an outside source.    It pertains to the comparative accuracy rates of meteorologists and astronomers.    


"I am an avid sky watcher and I am a weather nut.      I noticed that the predictions of weather forecasters are often wrong, but astronomers always get their predictions right.    Why are astronomical forecasts so much more accurate than weather forecasts?"
      -Rob W,  Skowhegan

While this question presents us with a beautiful opportunity to coat astronomy in four layers of glory, we will instead be quite charitable.

The simple reason that weather forecasts are sometimes less accurate than astronomical ones is that the astronomer contends with far fewer variables.  For instance, in the solar system, the mass difference between the Sun and planets is so great that one could consider planetary motions to involve nine two-bodies problems, those that can be solved exactly.  
The meteorologists have to deal with air parcels that have different pressures, temperatures, humidity levels, and even compositions.   These  parcels react with other air parcels while the Sun shines at different intensities along a planet whose surface consists of variegated patches of materials that radiate and absorb heat at different rates.  Earth's weather system is a sub-chaotic system, meaning that precise predictions are not possible.   You might have heard of the "butterfly effect," the notion that a butterfly flapping its wings in Brazil might cause a tornado to form in Kansas.  This fanciful statement merely means that meteorologists cannot account for every single air parcel because, for one thing, they can't measure the conditions of each one and two, these measurements, themselves, are limited.  
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Of course, astronomical predictions are also limited.    Even though astronomers can accurately predict eclipses and planetary positions tens of thousands of years into the future, there comes a time when the predictions become uncertain.    We cannot tell you the specifics of eclipses or planetary positions a million years from now.   There is a measure of uncertainty in solar system dynamics that precludes astronomers from knowing conditions indefinitely in the future.     However, since astronomers deal with fewer variables, these errors won't become troublesome for quite a while.

P.S.   I hope the meteorologists on this list-serve do not feel slighted by this article, which we wrote with the type of exuberant joy that three straight weeks of dreary weather invariably engenders in people.