Hold still, I think I see a nit!
The rate of change of the declination at the equinoxes is 24 arc-minutes per day, approximately equal to the size of the image of the solar disk, so if the spot is perfectly centered on the line at dawn, by dusk it should be nearly off one side. Actually, this i
That's a horse of a different color. Then you have a geometrical image of the hole rather than a pinhole image of the sun. The lack of "perfection" remains, but is no longer so apparent. Now you might want to ask for how many days around the equinox the image stays "pretty much" on the line.
Here, in our planetarium, we often say that the Moon is running
on the Sun's path, 6 months later.
summer : Sun's high, Moon's down
winter : Sun's down, Moon's high in the sky;
It's an easy, but not too wrong tip for non-astronomical public.
It may not be "too wrong", but it is w
If only one could rely on that! Sadly the variation between successive
measurements even over say an hour - and even with one of Tony Moss's
excellent declination measurement devices - is such that one has always to
make some average estimate and possibly eliminate from that avearage the
highe
BUT... is anything unbiased??? I think that the calendar months are season
neutral? They don't seem to have the right ring though, in English anyway.
Whatever you settle on, make it something I am able to remember, or figure out when I hear it. I am just able to remember that "vernal" has s
There's a question I've been pondering for years now, maybe somebody can help me. You know that idiot savants are rare individuals with extraordinary ability in one narrow area, and often intellectually and emotionally deficient in all other areas. A common form of this phenomenon is the abilit
Hi Richard,
It seems you have reinvented Piet Hein's helical dial. See the home page of
Egeskov Castle, http://www.egeskov.dk/english/sightseeing/index.htm
and click nr. 25 on the map or in the list below it.
John Moir showed already that the dial does not function well outside the
equinoxes in
I did spend some time on the maths and, if you get it right, then each surface is actually required to bend in only one direction at any point so bending should work. Good point about lumps, bumps and other irregularities though. This isn't a problem with 60 thin hexagonal sheets, of course, but
I give an explanation of this ill-behavior in my website:
www.fransmaes.nl/sundials, choose Index and goto Kvaerndrup.
I think I have a quantitative handle on this now. So we don't have to worry about hyperbolic surfaces and such, let's simplify the twisted strip by removing everything except t
In fact, in Piet Hein's dial (and in John Moir's
model) the time is read not from the lower part of the helix, but from its
center line. We could therefore omit one coil of the helix and insert the
center line into the analysis. This would bisect the deviation you calculate
to some 20 minutes, wh
> As for latitude, isn't it true that everywhere on earth gets an average of
> 12 hours of daylight over a year?
No that's NOT true! What does "everywhere" mean? If "everywhere" includes
the the dial face of a north wall dial, then it's not true. If you mean the
"flat" saurfacew of the earth, t
Isn't it the contrary?
I thought we at Northern latitude were the lucky ones to have more summer then winter time.
Damn. There nothing worse than being pedantic and then making a sign error.
Thanks, Fer.
--Art
Quoted from a Google search of the encyclopedia Wikipedia:
Plekhnatons
The ancient Greeks used a type of sundial called a plekhnaton. The gnomon was a rod or pole upright in a horizontal face or half-spherical face. The shadow of the tip of the rod sweeps out hyperbolic curves on a flat face,
Photos of the Sun Dagger at various times can be seen here:
http://www.cpluhna.nau.edu/People/sw_archaeoastronomy.htm
The following page gives a concise description of the Sun Dagger in relation to Sun and Moon.
http://paganastronomy.net/nahist.htm
At Chaco Canyon, we find the most famous
My interest is personal, not professional, so I can't answser most of your questions. My educated guesses are no better than your educated guesses.
For the physical structure and possible history of the petroglyphs:
http://www.angelfire.com/indie/anna_jones1/sundagger.html
Good site, It
In regards to the spiral representing 18.6 years (and not 18.5 or some other close number), I believe the answer is that the observations are directly tied to the 18.6 year cycle. So, if the observations were properly recorded, the spiral would indeed represent 18.6 years.
Albert Franco
Do y
The photo at top of the linked page makes me feel certain that the petroglyph was intentionall drawn to represent the location of the Sun in the sky.
Then the photo has fulfilled what I believe to be its purpose, namely to make you feel certain of that. If my arguments are correct, a very simil
*
For example, at summer solstice, during the 18 minutes when light shines through the right gap, the sun has moved 4.5º westward almost horizontally across the sky. We would at first glance expect the projected pattern of sunlight to move horizontally across the spiral, shifting to the right
I've just realized, thinking about it again, that the simplest realization of a 'helical' dial is a single sheet of metal given a half-twist of 180 degrees. So long as the edges are straight and the twist is distributed uniformly then the desired "line o'light" effect will be achieved.
And so we
I used Photoshop's image distortion, skew and perspective features
extensively to "fix" many of the photos on the site so that it looks like
the camera was centered in front of the center of the dial faces.
Keep in mind that the gnomon in the processed picture will be "funny". If you only use
There is no proof that can be observed with the naked eye that the earth is not the center of the universe. The motions of the sun moon and planets, including the equation of time, tides, eclipses etc., are all adequately described by the geocentric model. We do not need to accept the revolutiona
W, the Foucalt Pendulum would prove that the Earth rotates, but I
don't think it gives any evidence that it revolves about the Sun. What
could we do to take it a step further?
It does in principle, but it would be hard to get the accuracy. Other things, like parallax and astronomical a
Thinking again about Foucalt's pendulum, I realize you're right: It makes
a full turn (if situated at one of the poles) in a sidereal day, doesn't
it? That would put it "off" a full day each (solar) year.
What does happen at the equator, say? Simple geocentric mechanics would
have the pendulum s
You write,
Foucault's Pendulum may be a good demonstration of rotation but can we call it a proof? I have yet to see one provide consistent long term information? It is too subject to minor perturbations to show anything other than the latitude effect. The solar/sidereal difference noted by Dav
This led me to consider an offshoot of the skylight concept. Some of my neighbors have installed a "solar tube" which provides a skylight effect in a remote room by reflecting the sunlight down the shiny inner wall of a tube roughly one foot in diameter. The light emerges at the lower end of th
Why was the transit of Venus - really - so important in the determination
of the size of the solar system? Although a transit of Mercury has a less
favorable geometry, i.e., all other things being equal the accuracy is less, it
happens all the time. Wasn't it used? Coulnd't the frequency of m
Aristarchus of Samos (?310-230BC) used the shadow line
of the moon to estimate the distance to the sun. According to http://www-astronomy.mps.ohio-state.edu/~pogge/Ast161/Unit3/greek.html,
he "Showed geometrically that the Sun was at least 20x further than the Moon.
Really 400x further: sound
Thanks for the replies, but ...
The geometry and the calculations are not hard, but I question the
possibility of a significant observation. Aristarchus of Samos claims
18 < D < 20. That implies an astounding ability to
determine when the Moon is exactly halved. If you draw a line between t
In einer eMail vom 13.6.2004 20:50:17 Westeuropäische Sommerzeit schreibt
[EMAIL PROTECTED]:
1. How does it solve for the astronomical
unit, the absolute distance from the earth to the sun? I understand that it
solves for the ratio of the distances earth to sun and earth
to moon, bu
BTW, I have the formula for working out Easter if anyone's interested.
*The* formula? The Catholic and Orthodox churches celebrate Easter on different dates because they use different formulas. At least they both use formulas (I believe). Astronomical definitions are also possible, which woul
Appendix III of Meeus's magisterial "Astronomical Algorithms, 2nd Edition" contains the most important periodic terms of the planetary theory VSOP87. I don't feel like keypunching 40 pages of numbers and so was wondering if anyone on the list knew of a digital source for the numbers.
You could a
In einer eMail vom 2.7.2004 18:38:46 Westeuropäische Sommerzeit schreibt
[EMAIL PROTECTED]:
So, you don't need the magnifying effects of a
glass sphere in order to feel the temperature difference. The
sun alone is strong enough.
In Tucson.
--Art Carlson
In einer eMail vom 16.2.2005 02:33:07 Westeuropäische Normalzeit schreibt
[EMAIL PROTECTED]:
It isn't
quite a sundial, but it has an analemma (see pic half way down webpage),
solstice markers and equinox markers, and stuff to do with polynesianstar
navigation.
Neat. But the analemma
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