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September 1999, Week 3

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Subject:
From:
Denis Bogan <[log in to unmask]>
Reply To:
Vermont Skiing Discussion and Snow Reports <[log in to unmask]>
Date:
Wed, 15 Sep 1999 12:50:34 -0400
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>From:    "Mark P. Renson" <[log in to unmask]>
>Subject: NORTHERN LIGHTS?
>
>        The Mount Washington weather report from Monday reported the
observation
>of northern lights.  Did anyone in Vermont see this?  How vivid was it?
> How common is it to see this phenomenon in Vermont?  We Flatlanders don't
>have the opportunity to see them, at least not to my knowledge.

Northern Lights or Auroral displays are infrequent south of ~ 45th
parallel.  I do remember they were occasionally seen in the Boston area
when I was a kid, but I've still never seen them.  About 2 or 3 years ago
there was a very intense display with perfect observing weather on Mt.
Washington.  A story and photos were posted on the Observatory web page.
Perhaps they are still there.  I couldn't find them but I am not a web
search wizard.  If someone finds them please send me the link.

Favorable conditions for aurora can be predicted with a couple of days lead
time.  Aurora are excited by the solar wind, a constant stream of ions with
energies in the thousands of electron volts.  These ions are deflected by
the earth's magnetic field.  The defection is greatest in the equatorial
regions and decreases steadily toward the poles.  There is a singularity at
the poles with no deflection occurring there.  As a result, the energetic
ions penetrate into the upper atmosphere where they produce highly excited
atoms and molecules that emit light.  Anything that markedly increases the
solar wind will cause an increase in auroral displays, sunspots, solar
flares, sun storms, etc.  The solar wind takes a couple of days to reach us
while light takes about 8 min. so when new solar flares or sunspots are
reported look a few days later if the weather is good.

I got another neat astronomy note from my son today that I'll pass on.

__________________
..The partial eclipse at the Duomo

  Natural phenomenon meets ancient scientific instrument

    Three weeks before last month's solar eclipse, Mark Gingrich <grinch
    at rahul dot net> posted a request to several astronomy newsgroups.
    Gingrich knew that many central European churches and cathedrals are
    set up as giant pinhole cameras -- they feature a tiny hole in the
    dome or cupola and an inscribed meridian line somewhere inside. When
    the sun's projected image crosses the "noon mark," it's noon local
    time. The most famous such arrangement was designed 350 years ago
    by the astronomer Gian Domenico Cassini for the Church of San Pet-
    ronio in Bologna, Italy. Gingrich asked for photos of the partially
    eclipsed sun as it crossed the meridian lines in these historical
    scientific instruments. Gingrich's request bore fruit and Franco
    Martinelli has put up this page [28] with the results. Many thanks
    to TBTF Irregular [5] Mary Ellen Zurko for the pointer.

    [28] http://www.nauticoartiglio.lu.it/almanacco/Aa_ecli_13.htm


Denis Bogan

[log in to unmask]   NOTE NEW e-mail ADDRESS!!!
Voice;  301-286-1306
FAX;  301-286-0212 - Let me know it's coming.
(Mailing address: Laboratory for Extraterrestrial Physics
Code 691, NASA Goddard Space Flight Center, Greenbelt, MD 20771)
http://www-691.gsfc.nasa.gov/personnel/dbogan/dbogan.html

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