Tony Moss wrote:-
snipHappy New True Millennium to you all snip
Just to keep the thing continuing for as long as possibe - if all this
millennium hype is to celebrate 2000 years since the birth of Christ - why
are we celebrating on the 1st January? Shouldn't we celebrate the event on
25th
[EMAIL PROTECTED] wrote:
I saw Cast Away last week, and had a question about sundials and the
movie.
After Tom Hanks has spent several years on a desolate island, he constructs
an impressive analemma from a thin beam of light that enters his cave,
complete with days of the months.
Thanks, Bill, for once again politely answering a dumb question. You
probably won't believe that for our new house in Brattleboro, which
has a wall facing 46.56 degrees east of south, I'm just completing a
combination noon dial, featuring a local apparent noon vertical line
as well as a
Hello all:
We watched the Christmas partial eclipse using a telescope to project an
image of the sun onto a white piece of stiff paper. I fitted the large end
my 4 refractor with an 18 square piece of cardboard with a 4 hole cut
into it so that the cardboard would shade the viewing screen at
From the web page:
http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/SEgeometry.html
Eclipse geometry is complicated by the fact that Earth's orbit around the Sun
is elliptical. As a result, the Sun's apparent semi-diameter varies from 944
arc-seconds at aphelion to 976 arc-seconds at perihelion.
It is true, however, that the difference is observable in page-size photographs
that
lie side by side on a table. There is an old project physics activity that has
the
student plot the distance to the sun based on changes in the apparent size of
the
sun; and from this data you can computer
Hi John,
Does anybody know the difference in the apparent diameter of the sun, in
degrees, between perihelion and aphelion? Is this significant?
The info you want is in the BSS Glossary (plug, plug!) under semidiameter.
The answers are 15.76 arcmins in July (aphelion) and 16.29 arcmins in
I suspect that the analemma, being familiar to the public on globes,
sundials, etc., was used solely for that reason, call it artistic license.
Sun position lines (corresponding to the latitude dimension of an analemma)
were marked on the floors of some cathedrals. See J. L. Heilbron's 1999
I haven't tried to measure the variation of sub-tended arc of the Sun's
disk but have read (URL below) of it being done for the Moon, an approx.
14% variation. However, with an enlarged solar image, via a Heliostat,
perhaps the 3% variation (mentioned below) could be be teased out.
Warren Thom contributed:
(2) In the cave the shape of the hole went over his face. But light rays
come
into the cave in parallel lines -- so the shadow should be as large as the
hole
not as small as his eye/nose.
I am glad I am not the only one who notices such things.
By no means! I'm
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