received this just now:
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What will future civilizations think of Manhattan Island when
they dig it up and find a carefully laid out network of streets and
avenues? Surely the grid would be presumed to have astronomical
significance, just as we have found for the pre-historic circle of
large vertical rocks known as Stonehenge, in the Salisbury Plain of
England. For Stonehenge, the special day is the summer solstice,
when the Sun sets in perfect alignment with several of the stones
signalling the change of season.
For Manhattan, that special day comes today Tuesday, May 28;
one of only two days in the year when the Sun sets in exact alignment
with the Manhattan grid,
fully illuminating every single cross-street
for the last ten minutes of daylight. The other day is July 12. If
Manhattan were perfectly aligned with the geographic north-south
line, then our special days would instead be the spring equinox, and
if we so designated, the autumn equinox -- the only two days on the
calendar when the Sun rises due east and sets due west. But
Manhattan is rotated 30 degrees west from geographic north, shifting
the days of alignment elsewhere into the calendar. Upon studying
American culture, and what is important to it, future anthropologists
might credit the Manhattan alignments to be cosmic signs of Memorial
Day and, of course, baseball's All Star break.
Because Manhattan is so small (13 miles long) compared with
Earth's distance to the Sun (about 93 million miles), the Sun's rays
are essentially parallel by the time they reach Manhattan, allowing
the Sun to be seen on all cross streets at the same time, provided
you have a clear view across Manhattan to the New Jersey horizon.
Note that some major streets cross the entire island without
obstruction, including 14th Street, 34th Street, and 42nd Street.
While only today's sunset qualifies as the exact day for this
auspicious moment, every other day this week will also work, as the
sunset point migrates slowly north from day to day along the horizon.
This migration brings with it an ever-lengthening day. Indeed, days
get longer until summer begins on June 21st, and then get shorter, as
they must, for every day of the summer. An obvious fact when you
consider that the first day of summer, June 21, is the longest day of
Sunset takes place all week between 8:20 and 8:25PM EDT, at a
street near you.
As always, keep looking up.
-Neil deGrasse Tyson
Neil deGrasse Tyson
Department of Astrophysics
& Director, Hayden Planetarium
Division of Physical Sciences
American Museum of Natural History
Central Park West at 79th Street
New York, NY 10024
Posted by at May 28, 2002 02:12 PM
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