Hi All,
very interesting issue, so after all:
with a verticle mirror with the right azimut you could turn the famous
analemmatic sundial so the the line with the dates is on a path which is not
north-south! and the ellips will be alligned with this path
looks to me that the issue can be solved after all.
One has to investigate if the dimensions of the mirror are realistic and you
will need 2 mirrors (or 2 sundials) to cover the whole 24 hours .
If the azimut of the path is alpha, the mirror should be at alpha/2,
kind regards,
Hendrik
---------------------------------
Analemma Sundials
H J Hollander
Fixed +31 20 6374383
Cell +31 616 462 879
[EMAIL PROTECTED]
www.analemma.biz
lat 52 23' long 4 57'
----- Original Message -----
From: Chris Lusby Taylor
To: John Carmichael ; [EMAIL PROTECTED] ; [EMAIL PROTECTED] ;
sundial@uni-koeln.de
Sent: Monday, June 09, 2008 7:38 PM
Subject: [SPAM]Re: Advice wanted, on 'Analemmatic' sundial orientation
Hi John et al,
I thought at first that John Lynes was making a joke, but you could actually
do this. If you have a large, fixed, plane mirror you can use the sunlight
reflected off it instead of the actual sun. By suitably angling the mirror you
can make the sun appear to rotate about any desired axis, not just the earth's
axis. So, you can make it appear to rotate about the local vertical, just as it
does at the Poles. So, just as at the Poles, an analemmatic sundial using the
reflected light will be circular and the gnomon/person will not need to be
moved for different seasons. But the numbers will go round anticlockwise, which
might cause further objections!
The actual angle you'd need is this, I think: take a vertical mirror, facing
south, then lean it towards the north at (90+latitude)/2 to the horizontal. For
40 degrees North this makes 65 degrees. So, it's facing the southern sky, as it
were. If it were a dialface we'd say it was a direct south reclining dial. Fix
it there. Now, put a vertical gnomon close to the bottom centre of the mirror
and mark out a perfectly semicircular, equiangular dial around it. It will work
from 6am to 6pm throughout the summer. Or, if you want the user to be the
gnomon, just mark the spot where they must stand.
In the winter months, as John said, the sun's too low in the sky for the
reflection to shine on the ground.
A mirror of, say, four feet high and eight feet wide would work well. It
doesn't have to be 100% perfect optical quality. Users should back up to it to
avoid being dazzled, I suggest. I think this is an excellent solution to what
at first appeared an impossible brief.
Regards
Chris
----- Original Message -----
From: John Carmichael
To: [EMAIL PROTECTED] ; [EMAIL PROTECTED] ; sundial@uni-koeln.de
Sent: Monday, June 09, 2008 3:42 PM
Subject: RE: Advice wanted, on 'Analemmatic' sundial orientation
Hello John L.
I’ve never heard of such a sundial and I can’t imagine how it would
function. I’m not sure I understand the setup and positioning of the mirror.
Is the mirror permanently fastened to the ground or is the mirror moveable?
Does the mirror reflect sunlight onto the sundial face, or do you read the
sundial by looking at the face’s reflection in the mirror? I just don’t get
it. It sure would be helpful to see a drawing if possible.
Puzzled in Tucson
John C.
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL
PROTECTED]
Sent: Monday, June 09, 2008 4:08 AM
To: [EMAIL PROTECTED]; sundial@uni-koeln.de
Subject: RE: Advice wanted, on 'Analemmatic' sundial orientation
Dear Alison
One expedient, at least in theory, would be to fix a plane mirror,
suitably angled in plan to the main driveway and tilted to convert the
analemmatic sundial ellipse into a circle. The position of the human gnomon
would not vary with the season. The sundial would receive reflected sunlight
only on six months of the year, during the summer months, but this is when most
visitors would be around.
Unfortunately you would need either an enormous mirror or a very
modest analemmatic sundial.
John Lynes
-----Original Message-----From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Behalf Of Alison ShieldsSent: 03 June 2008 18:57To: [EMAIL PROTECTED]: Advice
wanted, on 'Analemmatic' sundial orientation Dear Sundial Experts, I have
recently joined this Mailing List, and hope that any memberswill be able to
give me some assistance on the following situation. Our local Stately Home
("Kentwell Hall", Long Melford, Suffolk) isconsidering installing an
Analemmatic sundial, as a new interactiveattraction for visitors - but we are
getting 'conflicting' advice,on whether this 'Human Sundial' will work in the
way we want it to. We have been in discussion with "Modern Sunclocks"
(apparently theacknowledged 'experts' for these features), who have told us
thatits central scale of dates must be aligned North/South - plus thathour
markers must be correctly positioned on an elliptical ring,and which would lie
on the Northern side of that scale of dates. Photographs on their website (
www.sunclocks.com ) confirm this. However, our 'Director of Operations' (Mr
Phillips) absolutelyINSISTS that he wants the scale to run exactly parallel
with ourmain driveway - on a compass bearing which is about 162 degreesfrom
North, with the hour points placed on its Southern side. He also wants the hour
points to form an exact semi-circle, andnot be elliptical in shape. Mr
Phillips refuses to accept thathe cannot arbitrarily position the Human Sundial
feature as hewishes, and says that it must be possible to create this so thatit
could then align with the existing layout of buildings/paths. Can anyone on
this Mailing List tell me whether it is possible toinstall a Human Sundial to
fit any existing orientations, (withappropriate re-calculation of its component
parts) - or, if not,just confirm that it must be as "Modern Sunclocks" have
told me. I can then show the 'weight of evidence' to Mr Phillips.
Because"Kentwell Hall" is a well-known Stately Home (open to the public),we
should not want to become a 'laughing stock' by installing afeature which does
not work - despite Mr Phillips assurance that"all types of sundial can be
adjusted to work, in any location". Looking forward to all comments (to this
List, or sent privately). Sincerely, Alison Shields.
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