Hi Kevin (and Peter R et al),
I saw your SML post and will watch with interest what responses it gets.
One point, though: the value of 1.27 mm/sec as the lower limit of perception of
movement is impossibly precise! I suggest that you would get +/-50% variation
between different observers. Also, it will depend heavily on the situation:
watching a laser spot on a piece of graph paper will give a value orders of
magnitude different to following a distant aircraft on a clear blue sky. What
really matters is the rate of angular change and a stationary reference point.
Regards,
John
----------------------
Dr J Davis
Flowton Dials
________________________________
From: Kevin Nute <kn...@uoregon.edu>
To: sundial@uni-koeln.de; Peter Ransom <pran...@btinternet.com>; JOHN DAVIS
<john.davi...@btopenworld.com>
Sent: Tuesday, 6 August 2013, 21:38
Subject: Visibly Moving Gnomon Shadows
The movement of the gnomon shadow at the famous Samrat Yantra equitorial
sundial in Jaipur is reputed to be clearly visible to someone standing near the
projection surface. I've read it moves as fast as 1 mm/s, though obviously not
all the time. At a given latitude, say 40º N, can anyone suggest a simple
formula for estimating how far a projection surface would need to be from a
vertical or horizontal gnomon for the shadow to move at 1.27 mm/s (the
practical lower threshold of perceptible movement) I wonder? Or in other
words, what's the smallest sundial you could build to see real-time movement of
the gnomon shadow with the naked eye?
Kevin Nute
Professor of Architecture
University of Oregon
School of Architecture and Allied Arts
Eugene, OR 97403
USA
kn...@uoregon.edu
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