Hello Sundialers
When Bill didn’t sign his last letter, I
thought he was following in Patrick Moore’s footsteps.
As you probably already know the great man replies to all his letters on
a 1925 typewriter, I think it’s a Remington and anybody lucky enough to receive
a letter from this colossus will know that he does not sign his
correspondence. I do not think it
has anything to do with saving time because any young aspiring astronomer who
writes to him will get a very full and encouraging letter in return, by return
of post.
If anyone in the group has had a letter from
the great man ‘providing it was not of a personal nature’ I would be very very
grateful if they could send it as an attachment to me.
Thank you all for your most interesting and
informative letters, I do not understand the formulas in every one of them but
it has given much pleasure looking attempting to understand them, I could not
retire for the night without checking the latest letters on the group.
Your oldest student
John
52.27 N 2.44W
-----Original
Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]On
Behalf Of [EMAIL PROTECTED]
Sent: 22 January 2002 19:39
To: [email protected]
Subject: RE: Marking Ceiling
Dials, Addenda
I
forgot to add a note and to sign my last message. Sorry for the
duplication.
Sundialers,
A convenient way to mark the center of the
sun's image made in a reflected ceiling dial is as follows. Punch a hole
approximately 1 mm in diameter in the center of a 3" x 5" file card.
Hold the card in the beam of reflected sunlight a few inches from the
ceiling. Adjust the card perpendicular to the beam to get a circular
image of the sun with the pinhole centered in the image. The light coming
through the pinhole will indicate very closely the desired point on the
ceiling. Mark this point and label it with the appropriate time and/or
date. The accuracy of this method depends on how accurately you can hold
the pinhole in the center of the circulate image of the sun. I can get
consistent results within about 10 seconds.
If one thinks of the inverse of the above
procedure: that is, forming a pinhole image of a nodus by holding a 1 mm
diameter hole in the fuzzy penumbra of its shadow, one will see a pinhole image
of the nodus, and, by centering the nodus's image in the circular image of the
sun, very precisely mark the center of the fuzzy shadow of the nodus.
This is one very useful interpretation of what has often been referred to
as a Shadow Sharpener on this list.
Bill
41d 58m N, 70d
41m W
