Hi Steve
I think your question is interesting.
Usually all the Sun compasses use declination of the Sun (through a
calendar), latitude and time (hour angle) to find the azimuth. This approach
need to know the time and the longitudine to get the local Sun time, that is
the hour angle.
With an altitude compass the hour angle is ignored, you use declination and
altitude of the Sun and latitude.
These instruments have the problem you point out, near noon they are
inaccurate not only because with a little change of altitude there is a
significant change in azimuth but you have also to know if it is AM or PM.
Near noon this may be a problem if you give up to the time.
Nevertheless I think this approach is very interesting because I do not need
time and longitude.
I risearched this kind of compass with 4 targets:
- it must be an altitude compass without know longitude and time
- it must be universal, for every latitude
- I don't wish to know the value of the altitude but to see it, with the
shadow of a style
- I wish to read the value of the azimuth but if possible I wish to see the
direction of the azimuth
I solved the question with an instrument similar to an astrolabe for the
points 1, 2 and 3 and, partially, for the point 4: I get the value of the
azimuth but not its direction.
Really I founded a solution to complete the 4th point but it is too much
intricate, I'm working to improve it.
Now I have not picture to send you, what I described is for the most part in
my mind, as soon as I have a picture, I'll send it to you.
ciao Fabio
Fabio Savian
[email protected]
www.nonvedolora.eu
Paderno Dugnano, Milano, Italy
45° 34' 10'' N, 9° 10' 9'' E, GMT+1 (DST +2)
-----Messaggio originale-----
From: Steve Lelievre
Sent: Saturday, May 10, 2014 4:28 PM
To: [email protected]
Subject: Altitude dials as compasses
Hello, everyone,
A recent NASS Compendium included an article on the use of a Shepherd's
Dial as a compass. The author reported orientation errors in field use
of up to 25 degrees in the hour either side of noon but 5 degrees or
less in other parts of the day. This is consistent with my findings from
with a similar dial that I tested last summer (although I didn't manage
quite the same accuracy in the non-noon period).
I'm currently designing a Capuchin dial adapted to a compass, but am not
expecting it to do well near noon either. The idea of portable solar
compasses based on altitude measurement is appealing because there is no
need to know time of day, but it seems inevitable that they're not going
to function well around midday while the sun hangs in the sky with
minimal change in altitude.
Am I missing some potential cleverness - given that I want a portable
dial with no need for a watch to determine time, would any other type of
dial be less prone to midday orientation errors? Are they particular
adaptions could be used to improve accuracy?
Cheers,
Steve
Herty, Frank B. (2014). A Shepherd's Azimuth Dial. The Compendium
[Journal of the North American Sundial Society], 21(1).
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