Speed. Some things move faster than others. When we viewed last
August's solar eclipse, in Tennessee, the Moon's shadow was
moving along the Earth at a rate of
about 1,450 miles per hour. Depending mostly on latitude, your
speed may be greater or less. Indeed, totality was sufficiently
exhilarating that we wondered when the would the next eclipse occur
in Philadelphia. These days, one can find practically any
information on the Internet, and eclipse locations was no
exception. We found
this page and simply typed in a date range, the type of eclipse
we were interested in (total), and the decimalized GPS coordinates
for Philadelphia (39.94 and -75.10). Unfortunately, a reasonable
date range (± 100 years) showed nothing. So we used the
maximum range available – the entire 5000 years between 1999
BCE and 3000 CE. That produced 14 Philadelphia total eclipses, but
again unfortunately, the last one took place fourteen years before
Columbus' first voyage. Even more
