Bryan, Steve
In Engineering it is common to use 10*log10(x) for example if x=3
10*log10(3) = 4.77. This has the advantage that 10*log10(10) = 10. Many
times these are described as units of decibels (dB). For example 3
watts is 4.77 dBW (decibel watts). Or 10 milliwatts is 10 dBm. When
Dan, Steve
Regarding the exact time of intersection: It requires a rather
interesting problem of simultaneously minimizing EOT and declination
between spring and fall dates. Fortunately I have a spread sheet that
implements the calculation of EOT to within a second or so and likewise
Dan,
You'd be surprised what you can do with a calculator and a note pad of
paper circa 1980. Back in the late 60's I used to compute comet orbits
using 7-place log tables and a Merchant mechanical calculator. Loved
the sound.
Regards,
Bob
On 2/22/2017 6:01 AM, sundial-requ...@uni-koeln.de wrote:
Do horologists worry about Allan Variance? I do
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Michael goes off looking for the ideal tropical year, perhaps ignoring
effects of the earth's nutations. I'll still take the one of 1900, most
importantly because it defines the SI second. Yes, I recognize that
we've now accepted the second using cesium (TAI = Atomic Time
International), and
I have used Pyephem (a Python programming module) for accurate
computation of solar transit and have put it to service to compute EOT
for Ken's latitude and longitude. However, doing it to the second is
pure fiction as the tropical year does not precisely repeat after 4
years cycle ... and
Kenneth,
Yes Julien Coyne has done a very nice job ... with limitations due to
solar declination. You can read about that and a number of other
digital sundial designs as well as my new digital design for 3D
printing. It will be in the NASS March edition of /The Compendium/. If
you don't
Yes, an interesting approach to designing and building a digital sundial
(see also www.sundials.org). I've downloaded the 3D files from mojoptix
and have just finished building a 3D printer to create one. However, in
taking a long look at his 3D model, the sunlight can only penetrate at
Computing the phase of the moon is complicated and no single table can
do it. Keep in mind the Metonic cycle where the phase of the moon (and
Venus) repeat their places and phase every 19 years. There's also an
approximate alignment repeat every 3 years of lunar phase that is the
basis for
Bill, Kevin
I too have been exploring 3D printing for a digital sundial (see
http://www.sundials.org/index.php/dial-links/videos/digital-sundials ).
Because I do a lot of programming, openSCAD is wonderful, allowing
precise control of shapes and allowing structures that until now were
only
Be careful about the shortest path. Of course you and the earth know
that a geodesic arc is the shortest path, cutting nearly a great circle
along the point from A to B. But map distortions give you a different
"view" and when you draw a straight line on a mercator, you have a rhumb
line.
Interesting digital dial. I must admit I looked at this design about 20
years ago. The author has one 3D moveable drawing of the completed
dial. If you look closely on the underside of the gnomon, there are
cut-outs of hour numbers that match the obverse side.
Therefore, this sundial works
3D printing has even made it to the National Geographic magazine ... and
the article clearly describes 3 different processes of 3D printing:
extrusion, laser sintering, and laser polymer adhesion.
The personal 3D printer is the extrusion type, using several different
types of plastic (ABS,
At an accuracy of 10 seconds, one not only must worry about correct EOT
adjustment and proper celestial alignment, but consider that all of the
dials that I know, including Bill Gottesman's Renaissance Sundial, are
built on strict geometric principles and ignore the refractive effect of
the
Kevin,
Welcome the the wonderful world of celestial mechanics ... you need to
have only six orbital parameters plus time epoch plus earth inclination
and sidereal spin, so total of 8 parameters are required
Bob
On 2/23/2014 6:49 PM, sundial-requ...@uni-koeln.de wrote:
Send sundial
Gianni,
The image displayed at
http://www.museogalileo.it/esplora/itinerari/itinerarituristicoculturali/lineasolemeridianefirenze.html
is a wonderful 3D reconstruction. The give-away is no penumbral
shadows. But it is marvelous. Who created it and what is the story of
how it came into
Dick and all,
It may not be in the sundial registry (no one has filled out the
submission form!), but NASS did report the dial. The 9-foot stainless
steel equatorial sundial was built and dedicated on June 9th, 2012 in
memory of Kathleen Fischer, a sixth-grade science teacher who inspired
Gianni and John,
I have just updated the links page on www.sundials.org and have given a
section to Sundials At Railroads. Any additional links or comments welcome.
Bob
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Sara,
It is curious that the artist copied a vertical dial face onto the
horizontal dial implied by the pedestal. And the gnomon, reminiscent
of a vertical style appears to be upside down Hmmm, was this intended
as subtle humor or more of a slur against the Irish Fool?
Bob
Tony,
Please fill out the NASS sundial registry form at
http://sundials.org/index.php/dial-registry/submit-a-sundial and provide
pictures. Larry McDavid prefers photos of the sundial sans people. But
we should make sure this dial gets into the NASS sundial registry.
Thanks
Bob
Robert
The NASS website www.sundials.org has suffered a significant outage due
to the severe thunderstorm that hit the Washington DC - Maryland -
Virginia area on Friday, June 29th. The storm ranged from Ohio through
West Virginia and into the metropolitan area of DC, Northern Virginia,
and
Alex caught a typo in my procedure ... the sine of gamma, the arc
distance should read:
sgm = sqrt (sDsC*sDsC + sDcC*sDcC)
Bob ... Thanks Alex !!
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Axel,
This is a far cry from Eratosthenes measuring distance by the time of a
Camel caravan, but it should help do distance problems: If we consider
the earth a sphere, then the distance between two points on the earth
and azimuth from one to another is as follows:
Let site1 have lat1 and
Ruben,
I've featured your beautiful cosmic room at www.sundials.org.
Regards,
Bob
Robert L. Kellogg
NASS webmaster
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Larry and all,
Yes, I read that too. A better description can be found on the NASS
website http://sundials.org/ Its about 2/3 down the front page.
Bob
Robert Kellogg
NASS webmaster
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I have found the discussion of AD/BC, and CE/BCE a bit off-center. The
argument of AD/BC goes that it is representative of the birth of Christ
as the marker for our year count. Dionysius, under direction of the
Pontiff set the year one as that of Christ's birth. But several things
conspire
I am not receiving photos via the mailing list, getting messages such as
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Nicola and all,
I am sorry to hear of Giacomo's passing. I have posted your letter at
http://sundials.org
Regards
Bob
Robert L. Kellogg
NASS Webmaster
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Ahhh ... that you should advise Pope Gregory
Bob
On 10/7/2011 1:07 AM, Roger Bailey wrote:
The topic of this mailing list is sundials with solar time being the
essence of time.
In one forum we have debated the calendar, including its reference
point and nomenclature.
We have also discussed
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