Curiosity Dept: Ice sundial
Title: Message Dear All, Yesterday I was looking at the nice sharp shadowof an ice scupture about 3 foot high and I realised that it would be possible to make a sundial out of ice! Does anyone know if this has been done and are there any photos on the web? Thanks David
Analemma Photos article at Wired.com
Title: Message Dear All, Thought you may like this ... http://www.wired.com/news/technology/0,1282,65428,00.html David For sun related calculation needs ... visithttp://www.sunlitdesign.com/products/thesunapi/
RE: Precise EOT Program - Correction
Hello Gianni, Fer and John, Yes you are correct. December 22-23. I had another look at my spreadsheet and found that I had misread it. All the best David -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gianni Ferrari Sent: Saturday, 14 June 2003 9:20 PM To: sundial@rrz.uni-koeln.de Subject: Re: Precise EOT Program Hello John, also I have found the values given by Fer. The maximum change of the EOT , between the local noons of two consecutive days, is, in 2003, equal to 29.98 secs - 22/23 December. Within December 20 and 25, the changes are around constant and equal to 29.90 - 29.98 sec In 2004 (leap year) the maximum of the EOT change occurs between 21 and 22 December, and it is equal to 29.8 sec A regard Gianni Ferrari 44° 39' N 10° 55' E Mailto : [EMAIL PROTECTED] - -
RE: seeking for an azimuth software
Dear Alain, Check out www.sunlitdesign.com/products/thesunapi David -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Alain MORY Sent: Saturday, 14 September 2002 3:51 AM To: sundial@rrz.uni-koeln.de Subject: seeking for an azimuth software Hello ! I'm searching for a soft that could be able to give the date and the azimuth of the sun, when a time is given. I made picture of engraved neolithic stones, at some precise times and I wanted to know if they could point one or more famous times in the year. Does anybody knows such a soft ? Alain MORY 47°57N 6°57E - -
Sundial Enthusiasts in Australia
Dear All, While I normally live in Kazakhstan, I am currently in Australia. I would love to hear (off list) from anyone in Australia with an interest in Sundials. You can email me at mailto:[EMAIL PROTECTED] or phone me in Sydney (02) 9585 2565 Thanks David Pratten www.sunlitdesign.com -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Richard Mallett Sent: Wednesday, 6 March 2002 9:13 AM To: [EMAIL PROTECTED] Subject: Re: Reflector Reply Change Reply to : Larry McDavid Why did we want this change? I'm glad of it (although I did not request it) because with my email software (NAVCIS) I can only reply to the originating address. All the other mailing lists that I belong to (such as the ones on yahoo groups) use the list address as the originating address, and I have never seen any objections to this method. If I want to send a personal email to the sender (which for me is comparatively rare) I just look for 'From: ' in the message header. Richard. E-mail from: Richard Mallett, 04-Mar-2002 - -
RE: On northern vs. southern dials
Title: Message Dear All, I will take an intuitivepunt on any point on the arctic circle as having maximum ratio of southern exposure to northern exposure. Can't prove it. David -Original Message-From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Anselmo Pérez SerradaSent: Sunday, 3 March 2002 9:27 AMTo: Sundial, MailinglistSubject: On northern vs. southern dials Hi everyone, Imagine an oriented wall (gnomonic declination equals to 0 deg in one side and 180 deg in the other), all of us know that the southern side is exposed more time to sunlight than the northern one, butwhere is this difference bigger? It is clear that in the equator and in the North Pole the rate is 50% to 50%, ie., both sides receive the sameamount of sunlight through a whole year, so there must be in themiddle some latitude where the differencebecomes maximal. Which is that latitude? OK, I know we can solve it easily by 'brute force' but is there a simpler method to determine that value? I didn't find it. Now that I remember, a kind of touristical question: in this month's issue of the spanish version of Scientific American there is an article by D. Savoie about sundials an in it he says that in the Place de la Concorde in Paris it was drawn a sundial (an Oughtred sundial I suppose) based on the obelisk erected there. Does anybody know if the lines are still drawn or were they erased? Anselmo Perez Serrada PS: My apologizes for Southern diallists (you all know about our Northern egoccentrism!). Just swap the words North and South.
RE: Polar ceiling sundial
The BSS sundial glossary has the following entry under Types of Dials: reflecting ~: these dials have no gnomon, but reflect sunlight by means of a semi-cylindrical mirror, set with the axis of the mirror parallel to the polar axis. The mirror reflects the light to form a caustic curve amongst the hour points. For the special case of the mirror having a cycloid shape, the hour points are equally spaced. Note that the term reflecting dial may also be used for ceiling dials. What is the typical dialface for a 'reflecting dial'? Are the comments above about semi-cylindrical mirrors apply equally to ceiling and wall dials? If a polar ceiling dial has an inclination of phi/2 what does having a mirror inclined at phi do? What is a caustic curve? David
Refraction
Title: Message Dear Dialists, I have been pondering the effect of refraction on dial performance. Refraction quoted at .1 degree to .5 degree apparent difference in altitude below 10 degrees of altitude, will impact the hour angle to some degree. See http://www.gcstudio.com/calcuse.htmlThese are average values - refraction (according to Meeus quoting someone) can vary by up to .3 degree at the lower altitudes. 1. It would seem to me that dials that attempt to tell time during the hourafter sunrise andhour before sunset could usefully take refraction into account. However altitude for a given hour angle changes through out the year. Are there dialslaid out with reference to average refraction effects? And 2. We know that Mean time + EoT = Apparent Time However because viewing the sun through our atmosphere's refractionis unavoidable - Is there establishedterminology to distinguish between Apparent Time (geometric) as just definedabove and Actual Observable Apparent Time (after refraction)? David
Did it pass unnoticed?
Title: Message Dear Dialists, Merry Christmas - and did it pass us unnoticed? Today at 2001/12/25 05:32:02 [UT] our dials and our watchesare running in synchronisation! David www.sunlitdesign.com
RE: accuracy
Dear Walter, Greetings. There is another factor which limits sundial accuracy to about +/-22 seconds. This is the variation in the value of Equation of Time from year to year within a leap cycle. See www.sunlitdesign.com/infosearch/sundialaccuracy.htm David www.sunlitdesign.com -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of walter.jonckheere Sent: Thursday, 20 December 2001 8:47 PM To: sundial@rrz.uni-koeln.de Subject: accuracy Greetings to all We all know that the atomic clock has the highest possible resolution, while for sundials 2 to 1 minute seems to be the best achievement. I have a feeling 1 second could be obtained considering what follows. ( I consider a second ideal as one can feel it, I mean it is a timespan well related to the human body, one second you live, the next you may be dead; it is also somewhat related to the heartbeat) Consider a horizontal sundial whith the 15 degrees hour lines; it is impossible to trace minute lines when keeping usual dimensions for the dial. However, if we go far away from the base point of the gnomon, the portion of the arc between 2 hours, becomes larger; so imagine we go to where 60 lines can be drawn between two adjacent minute lines and we keep only the top part of the line 11h59m59s and try to draw it on the ground related to a very accurate positioning of the local meridian. These data allow also to calculate the height of the gnomon tip. If both dimensions are feasable to realise, we would have the desired accuracy of one second; of course the positioning of the meridian is of paramount importance and probably the most difficult to materialise. ( is this a nice subject for a university ?) Of some important influence is the width of the gnomon. The indication of noon time is never accurate because of this width, while the shadow cast for the earlier hours, may be considered as a hairline and is thus more accurate, which means that the morning part of the dial is more accurate if the shadow hairline is taken into account for determination of the meridian. So in fact, sundials should have a gap at noon corresponding to the width of the gnomon, and the afternoon part should be calculated in function of the right hairline shadow related to a second parallel meridian. Very interested to read your comments Walter
RE: Query about solstices
Dear Fritz, Using Find Annual Feature function (sdxFindAnnFeatx)of the The SUN API www.sunlitdesign.com/products/thesunapi I get the follwing value for the solstice this December: December 21 19:21:30.7143 [UT] (which is +/- 10 seconds of the true value) Compare with http://aa.usno.navy.mil/data/docs/EarthSeasons.html which shows the value to the nearest minute. Using the Declination function (sdxDecl) we find the declination for this time on the 20th, 21st and 22nd: 20th -23:26:06.7694 21st -23:26:20.9605 SOLSTICE 22nd -23:26:06.8546 Which have the following differences from the Solstice 20th -0:00:14.1911 21st 0 SOLSTICE 22nd -0:00:14.1060 David www.sunlitdesign.com -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Fritz Stumpges Sent: Thursday, 20 December 2001 9:12 AM To: 'Frank Evans'; sundial@rrz.uni-koeln.de Subject: RE: Query about solstices This topic got me wanting to get a piece of pipe and try it! From my new Sky software, which I'm just getting to know, I found that solstice is at about 11:22 on the 21st. I then got the declinations on the day before and after at this time. But the sun changes only 14 seconds(arc)/day. This means that on the 20th it is -23deg26m14s and on the solstice it is -23deg26m28s. How does this compare with other sources for accuracy? Anyway, at this required resolution, it would take a pipe or earthen hole, 307 feet long, assuming a pinhole or? which could be resolved as 1/4 of an inch of movement (@307 ft!) This is to measure the actual movement that day with respect to the day before and day after. Is this correct? And if so, I doubt they really could resolve this. This is 130 times smaller than the apparent diameter of the sun!? What do you all think? There goes the fun I was going to have with this endeavor tomorrow. I'll be there celebrating this magical moment anyway, as I'm sure many of you will Cheers, Fritz -Original Message- From: Frank Evans [mailto:[EMAIL PROTECTED] Sent: Wednesday, December 19, 2001 11:46 AM To: sundial@rrz.uni-koeln.de Subject: Query about solstices Greetings fellow dialists, You don't have to have a clear sky on the actual day you are wishing to mark sunrise or sunset. Martin Brennan in his book The Stones of Time showed elegantly how the people at Newgrange in Ireland did it five thousand years ago with the rising solsticial sun shining down a long shaft into the immense earthwork onto auxiliary marks for adjacent days. More recently there is a simple noon line in Durham Cathedral dated 1829 with extra marks for five and ten minutes after noon. This line was simply a clock regulator, though. Frank, 55N 1W -- Frank Evans
RE: Sundial link
Mounting the sundial upside down so that the face is oriented as for Britian will make the hour numbers go the right way ... David -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of The Shaws Sent: Wednesday, 12 December 2001 10:06 PM To: [EMAIL PROTECTED]; sundial@rrz.uni-koeln.de Subject: RE: Sundial link I note that on the link it says:- If you're bringing a sundial from Britain and setting it up in Australia, does that take a considerable amount of skill, or is it just a garden ornament for them? Perhaps the slight snag that the hour numbers go round the opposite way might have been worth mentioning Mike Shaw http://homepage.ntlworld.com/jmikeshaw/ N 53º 21' 24 W 03º 01' 47 Wirral, UK. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.306 / Virus Database: 166 - Release Date: 04/12/2001
