Re: Marking Technique
Hello John, Firstly, congratulations on accomplishing so much. Nothing would please me more than to learn that my concerns are unfounded. >If we did our marking correctly, the biggest factor affecting precision will >be the straightness of the styles. I suppose this could be checked exactly >by using a laser, but lacking one, all we could use was our eyes. By placing >one eye at the base of a style, we could look straight up the edge of the >styles. We did see very slight undulations in the styles, but we >guesstimated that they were only between I and 3 inches, a very small amount >if you consider the enormous size of the sundial. These could only affect >the precision of the dial by a few seconds. Time will tell! I've taken a look at the first drawing (right after the photos) in the proposal. It is an elevation view from the west, that has a superposed set of lines that show about the largest layout possible using the side edges as styles. Looking at the labeled distances along the "ground level" northward from where the west edge meets ground level, a red line inclined at about 58.04° shows the intersection of an equinoctial plane with the (meridian) plane of the drawing, and two lines north and south show limits at the respective solstices, making angles of 23.4° with the equatorial line. All three lines converge to a point on the ground about 8.84 meters north of the southern limit of the base of the heliostat tower. The length along the ground from the origin of the west edge/style at the south to the convergence point of the three red lines at the north, scales out to about 51.22 meters. The distance within the equatorial plane from the convergence point to the style is calculable as about 27.1 meters. This line of course meets the style perpendicularly. At that distance, an arc of 0.25°, if rotated about this equatorial line, would trace out a circle of about 9.3 inches diameter. Thus at that distance, the time required for the 1/2° degree wide sun to pass through the meridian plane would be very nearly 2 minutes of time during which it would move about 9.3 inches relative to the style edge. Therefore, if the style's edge were to be laterally displaced 3 inches, the resulting error in time would be about 3/9.3 x 120 = 38.7 seconds of time, and a 1 inch wrong location of the effective edge would cause nearly 13 seconds of error. Bill
Re: Kitt Peak - the list of time marks
Hi Robert, Regarding the defining of your calculated values (times), I'm assuming that the sundial's shadow position would come from calculating the local solar hour angle in terms of standard mean time, if this is the case then you're already there. If not, then the calculated local solar hour angle, in terms of time, is local solar time. Standard mean time can be found by applying to this local solar time; a) the equation of time (EoT) and b) the time difference from the local meridian to the standard meridian. Cheers, Luke Coletti > In working with John Carmichael on the layout of the dial markers at Kitt > Peak we decided there was a need for a list of times for the 5-minute and > special markers (about 190 of them). The list would show > the marker time for the dial face and the standard time clock reading when > the shadow would appear at that marker. This second value would be Standard > Time plus/minus the EOT for that date/time (what > should you call it, it is not standard time, local mean time or local > apparent time). The EOT would change a few seconds over the course of the > day so each time should be computed individually. That > sounded like too much work and too much probability of error, so I wrote an > application that computes the values. You simply input year, month, date, > starting time in hours and minutes, ending time in hours > and minutes, increments (we used 5 minutes), the time zone, and whether > daylight savings is in effect. I also entered a list of special events > (sunrise/sunset for special days, high noon and, in our case, style > shift times). And I let the computer do the work. Viola! We had the list > without the pain! I e-mailed a pdf file to John who printed it on a plotter > so we had a poster-size printout. It turned out to be very > professional looking and a great help. > > > > Some of you may wind up in a similar situation. If anyone would like to use > my application, I would be glad to share it for free. It is a PostScript > file, which is a text file. All you do is edit it with any text > editor and open it with a PostScript viewer. You can then print it or > convert it to a pdf file. Very simple. > > > > The most popular PostScript viewer is GhostScript. It runs on any platform = > Microsoft windows, OS2, MacOS, Unix, Linux or VMS. GhostScript by itself > requires you to type in long Unix-like command > lines on the keyboard, so also get GSView so you have a user-friendly > window/mouse interface with your computer. These are free from the > University of Wisconsin at http://www.cs.wisc.edu/~ghost/ > > > > Robert Hough > > ShadowMaster > > 32.37N 111.13W -
Conference dials
Hi Dialling Colleagues, For those of you who were not at the British Sundial Society Conference at Exeter in April, I have now put pictures of the dials that I displayed there on my website. It has a new URL: www.flowton-dials.co.uk Look out for * a new page on portable dials, including a compendium, * some new brass horizontals * an interesting old slate dial on the "Restoration" page. If you spot any glitches with the site, I'd be grateful for a note. Regards, John - Dr J R Davis Flowton Dials N52d 08m: E1d 05m -
Kitt Peak - the list of time marks
Title: Kitt Peak - the list of time
marks
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In working with John Carmichael on
the layout of the dial markers at Kitt Peak we decided there was a
need for a list of times for the 5-minute and special markers (about
190 of them). The list would show the marker time for the dial
face and the standard time clock reading when the shadow would appear
at that marker. This second value would be Standard Time
plus/minus the EOT for that date/time (what should you call it, it is
not standard time, local mean time or local apparent time). The
EOT would change a few seconds over the course of the day so each
time should be computed individually. That sounded like too
much work and too much probability of error, so I wrote an
application that computes the values. You simply input year,
month, date, starting time in hours and minutes, ending time in hours
and minutes, increments (we used 5 minutes), the time zone, and
whether daylight savings is in effect. I also entered a list of
special events (sunrise/sunset for special days, high noon and, in
our case, style shift times). And I let the computer do the
work. Viola! We had the list without the pain! I e-mailed a pdf
file to John who printed it on a plotter so we had a poster-size
printout. It turned out to be very professional looking and a
great help.
Some of you may wind up in a
similar situation. If anyone would like to use my application,
I would be glad to share it for free. It is a PostScript file,
which is a text file. All you do is edit it with any text
editor and open it with a PostScript viewer. You can then print
it or convert it to a pdf file. Very simple.
The most popular PostScript viewer
is GhostScript. It runs on any platform = Microsoft windows,
OS2, MacOS, Unix, Linux or VMS. GhostScript by itself requires
you to type in long Unix-like command lines on the keyboard, so also
get GSView so you have a user-friendly window/mouse interface with
your computer. These are free from the University of Wisconsin
at http://www.cs.wisc.edu/~ghost/
Robert Hough
ShadowMaster
32.37N 111.13W
In working with John Carmichael on the layout of the dial markers at
Kitt Peak we decided there was a need for a list of times for the
5-minute and special markers (about 190 of them). The list
would show the marker time for the dial face and the standard time
clock reading when the shadow would appear at that marker. This
second value would be Standard Time plus/minus the EOT for that
date/time (what should you call it, it is not standard time, local
mean time or local apparent time). The EOT would change a few
seconds over the course of the day so each time should be computed
individually. That sounded like too much work and too much
probability of error, so I wrote an application that computes the
values. You simply input year, month, date, starting time in
hours and minutes, ending time in hours and minutes, increments (we
used 5 minutes), the time zone, and whether daylight savings is in
effect. I also entered a list of special events (sunrise/sunset
for special days, high noon and, in our case, style shift
times). And I let the computer do the work. Viola! We had the
list without the pain! I e-mailed a pdf file to John who
printed it on a plotter so we had a poster-size printout. It
turned out to be very professional looking and a great help.
Some of you may wind up in a similar situation. If anyone would
like to use my application, I would be glad to share it for
free. It is a PostScript file, which is a text file. All
you do is edit it with any text editor and open it with a PostScript
viewer. You can then print it or convert it to a pdf
file. Very simple.
The most popular PostScript viewer is GhostScript. It runs on
any platform = Microsoft windows, OS2, MacOS, Unix, Linux or
VMS. GhostScript by itself requires you to type in long
Unix-like command lines on the keyboard, so also get GSView so you
have a user-friendly window/mouse interface with your computer.
These are free from the University of Wisconsin at
http://www.cs.wisc.edu/~ghost/
Robert Hough
ShadowMaster
32.37N 111.13W
hemicyclium at cleopatra's needle
>Dear list members, IN the article The History of the Sundial : The Beginning of Recorded Time found at http://www.americanantiquities.com/articles/article14.html, I quote:' Almost 1500 years later, the emperor of Rome, Augustus (63 B.C. - 14 A.D.) moved Cleopatra's Needle to Alexandria, founded by Alexander the Great some three hundred years before. The hemicyclium in question was unearthed at the base of Cleopatra's Needle there; the numeral style indicates it was there after Alexander (about 332 B.C.). This artifact now resides in the British Museum.' In short, I am interested in learning more about this particular hemicyclium. Sincerely, Ronit Maoz Hi Ronit, Strictly speaking a conical dial, it has the reference 3086G in Sharon Gibbs 'Greek and Roman Sundials' Yale UniversityThesis which is published by Yale University Press, 1976. It has the British Museum ref 1936 3-9 1. Details are given by Gibbs as: H=404mm W=429mm (There are other measurements given there too.) The gnomon hole has a semicircular vertical section 50mm wide and 51mm deep. Eleven hour lines extend from winter to summer solstice. The three 'day' curves have been engraved always equidistant from each other and from the lower edge of the conical surface. Dots are visible at the junctions of hour lines and winter solstice line. Six shallow steps decorate the base. Seven greek letters have been engaved in the spaces below the equinox close to the right hour line. It was found in 1852 at the base of the needle in Alexandria. Gibbs says that it is a unique example of a conical dial with hours marked in Greek letters. The lettering is probably Byzantine but the museum has charaacterised the dial as Ptolemaic. Ref: A Guide to the Eguptian Collections in the British Museum, London 1909, p72 and p273. Also Mrs Gatty's Sundials pp42-43 There is a B&W photo (Plate 48) of the dial in Gibbs book. Hope this helps Patrick - E-Mail: [EMAIL PROTECTED] Web: http://ourworld.compuserve.com/homepages/Patrick_Powers/ Lat: N 51d. 49m. 09s: Long: W 00d. 21m. 53s -
hemicyclium at cleopatra's needle
Dear list members, IN the article The History of the Sundial : The Beginning of Recorded Time found at http://www.americanantiquities.com/articles/article14.html, I quote:' Almost 1500 years later, the emperor of Rome, Augustus (63 B.C. ñ 14 A.D.) moved Cleopatraís Needle to Alexandria, founded by Alexander the Great some three hundred years before. The hemicyclium in question was unearthed at the base of Cleopatraís Needle there; the numeral style indicates it was there after Alexander (about 332 B.C.). This artifact now resides in the British Museum.' In short, I am interested in learning more about this particular hemicyclium. Sincerely, Ronit Maoz
