RE: Spiral cut earth

Hi Brent, The spiral is not at a constant angle that could be incorporated into a dial.  It is true that the sun crosses the equator at only one point (time) during an equinox.  The crossing can actually be noticed over the period of a day on an accurately aligned equatorial sundial.  But at t

Earth line

Re the line on the surface of the Earth beneath the sun Wouldn't it be a loxodrome, at least for short lengths of time, since the angle with the meridian is nearly constant over, say, a day or so? John John Schilke, MD jfs...@ipinc.net

Re: Spiral cut earth

Ok great, now we are getting somewhere. So when we align our sundials to the north that also means we are aligning it East and West. Since the line of the sun from sunrise to sunset is not directly East to West but slightly skewed (explained by the spiral). Wouldn't it make for a more accurate su

Re: Spiral cut earth

Yes, this experiment shows the line for any given date and declination follows the latitude. It is a circle but not a Great Circle as shown with the string. The plane of a Great Circle goes through the centre of the earth. Latitude circles do not. Yes, the sun moves with latitude as the solar

Re: Spiral cut earth

Hi Roger; well I did that experiment. I'm not sure I did it right or understood what you are trying to teach me. The light travels along latitude lines as the globe turns. When I pull a string between two points it comes off the latitude line and is straight. That's what I expected. So the

Re: Earth movements

The short answer is that any coordinate specification has to be given in reference to a particular datum. Here's the Wikipedia article on datums: http://en.wikipedia.org/wiki/Datum_%28geodesy%29 > > Bravo, Tony Finch, for sharing this. I had no idea location was so > complex! > > Thank you. > >

Re: Spiral cut earth

Hi Brent, Just do it!. Get a globe and a cheap laser pointer from a dollar store. Shine the pointer on the globe and rotate the globe. Note several points. Then take a string and stretch it over the points. Is it the same line? A great circle? By the way, The shadow from any point is a strai

Re: Earth movements

Hi Hopefully the link below will help you. http://hpiers.obspm.fr/eop-pc/index.php?index=mission&lang=en Note that there is also a special note about this Japanese megaquake. Aimo Niemi http://pc-calculator.110mb.com/gnomon/ 2011/3/13 J. Tallman > Hello All, > > I just saw on the news that t

Re: Spiral cut earth

If the sun had a laser from its' center pointed directly at the center of the earth it would scribe that spiral line I was asking about. So maybe that spiral line is a time line? It would be local high noon under each spot the laser lit and advance one day each revolution. Sorry for the flurry

Re: bad sundials

For most errors on sundials there is an explanation. Sometimes the cause is a mystery. As for the special sundial in Company's Garden in Cape Town (South Africa) see http://www.wijzerweb.be/kaapstad.html (note that in the southern hemisphere the sequence of hour numbers on a horizontal dial is c

Re: Spiral cut earth

Put another way; When they say on the equinox the sun is directly above the equator maybe that is true for only one particular longitude on the equator. The equinox is not a day, it is a precise moment. So if I was on the equator on the day of the equinox and marked the sunrise and marked the s

Spiral cut earth

I was thinking that the sun tracks a straight line across each latitude line. So at an equinox the sun will be directly above the equator for one earth revolution and the next day it will shift a few degrees and be tracking a higher latitude. But that can't be right, we don't jump from one l

Re: Earth movements

Bravo, Tony Finch, for sharing this. I had no idea location was so complex! Thank you. Mac On 13 Mar 2011, at 13:44, "J. Tallman" <jtall...@artisanindustrials.com> wrote: I just saw on the news that the recent quake in Japan shifted the earth'

Re: Earth movements

On 13 Mar 2011, at 13:44, "J. Tallman" wrote: > > I just saw on the news that the recent quake in Japan shifted the earth's > axis by 4 inches and that the main island of Japan moved nearly 8 feet. > > Could someone on the list put this into perspective? As an example, I would > imagine that t

Earth movements

Hello All, I just saw on the news that the recent quake in Japan shifted the earth's axis by 4 inches and that the main island of Japan moved nearly 8 feet. Could someone on the list put this into perspective? As an example, I would imagine that the legal descriptions for property lines based o

Re: bad sundials

On 12/03/2011 19:39, Brent wrote: Hello again; I hope I am not trying your patience with my endless questions. Today I am thinking about all of the mistakes that I have made in my thinking about sundial designs. The motions between the sun and earth are more complicated than I first thought.

Re: bad sundials

John Carmichael wrote: <> == Hi John and everyone. Yes, I'm still alive and watching the list with interest. You're right (as usual), but I think you are remembering a short presentation that I did at a sundial society conference (NASS I think) some time ago. I