Contacter l'auteur / Contact the author

Recherche dans ce site / Search in this site

 

 

The solar analemma

The analemma of 13h UT over the ancient Erechtheion.

Text and pictures by Anthony AYIOMAMITIS

The weather factor (V)

The Internet is a great resource for weather conditions and forecasts. My preference during the duration of this project was Weather.com which not only provides hourly forecasts for both the current and the following day, in addition to  a ten-day forecast, but also permits for a subscriber to receive daily weather reports via email.

The online forecasts really proved their value during my first set of analemmas when heavy rains lasting a whole day had been predicted for Nov 22/01 as far back as a week earlier and which, regrettably, happened to coincide with my shooting schedule whereas the same forecast had been consistently predicting totally clear skies for the previous day (Nov 21/01) and partially clouded skies for the following day (Nov 23/01). Monitoring the weather and the associated forecasts up to the very early morning of Nov 21/01, I decided to go ahead and advance my complete shooting schedule by one day as a "preemptive strike" so as to be safe than sorry. Fortunately, this proved to be a very wise and propitious decision as the weather forecast was dead accurate for both Nov 22 and Nov 23/01!

The online forecasts

Yahoo Weather (World) - Reading (U.K.) - Meteo-France (F)

However, my incessant checks with weather forecasts would go against me for the most critical exposure of all, namely the Aug 30th cross-over point during the second marathon. If one were to check the ephemeris of the sun on April 12 or 13th (spring cross-over) and compare it to the ephemeris for Aug 30th (late summer cross-over), he/she would note that azimuth and altitude do not match up precisely (the latter is the preferred between the two). This deviation takes on a greater significance if the analemma is initiated at the start of the calendar year - the case for this set of analemmas - since it makes sense to forego the spring cross-over exposure and pursue the late summer exposure. 

The analemma of 14h UT over Zeus' Temple, ancient Nemea.

This rolling of the dice, however, namely that weather on Aug 30th will be suitable for imaging without any backup or supplementary exposure possible if the weather will not co-operate, proved to be a mistake. Weather forecasts on Aug 28 and early morning on Aug 29, 2002 persistently indicated three-day thunderstorms starting during the very early morning hours of Aug 30th, 2002. 

With much hesitation, the decision was made to image on Aug 29, 2002 so as to circumvent the anticipated storms the following day (had the forecast not indicated that the storms would last for three days, a decision would have been made to risk imaging as much as possible on Aug 30, 2002 and, if necessary, supplement any missing exposures on Aug 31, 2002 since supplementary exposures a day early (Aug 29) or a day late (Aug 31) are, in essence, the same). Of course, the weather on Aug 29, 2002 was less than ideal (thin clouds throughout) whereas the three-day forecast involving thunderstorms was completely off-base as pristine conditions characterized most of Aug 30, 2002. The thin clouds on Aug 29, 2002 fortunately did prevent the imaging of three of the analemmas (13:28:16, 17:00:00 and 18:00:00 UT) which were shot as originally scheduled on Aug 30th (13:28:16 UT analemma) or two days later (17:00:00 and 18:00:00 UT analemmas)!

Check the tables in the appendix

By way of conclusion

The pioneering work on the photography of the analemma by di Cicco (S&T, June/79, pg. 536-540) involved an unsuccessful first attempt at capturing the analemma due to the sun partially eluding the initial field of view. Regrettably, a similar outcome materialized with this project where the first six months of imaging (June to Dec 2001) had to be discarded due to a missed exposure which could not be substituted with an exposure a day or two earlier/later due to heavy clouds and rains over a period of about two weeks. Nevertheless, this failure did provide the foundation for a restart that would be uniquely characterized with imaging across one calendar year in lieu of twelve consecutive months spanning two years which is characteristic of each of the other successful analemmas to-date.

A total of 473 multi-exposures (11 analemmas with 43 images each) were originally planned during the 2002 calendar year so as to generate the analemmas depicted in Figures 3 to 13 and the composite graphic in Figure 14. Of these, a few dozen only were substracted due to physical obstructions that could not be circumvented in any way.

The analemmas in Figures 3 to 13 and associated breakdown  is not only a graphic illustration of the sun's movement across the local skies during one calendar year but also represent the physical characteristics and climatic conditions of the immediate region; the latter is something which became obvious as the project progressed and was reinforced by the need for a restart. A published report in one of the local newspapers on Feb 1/02 indicated that Oct/01 was the fifth driest October since 1927, Nov/01 was the fourth wettest November also since 1927 and Dec/2001 was the third coldest December since 1896 - dubious records which significantly impacted the initial part of this marathon and led to its premature end and consequent restart.

The analemmas described and presented in this article do indeed represent a most challenging and rewarding exercise requiring dedication, patience, perseverance, thorough advance and detailed planning, a (great) sense of humor (vis a vis numerous accidental film advances as per the earlier discussion), constant interaction with weather web sites as well as some degree of good fortune with the local weather and other intangibles such as unobstructed views, unforeseen problems with cameras, lenses, filters, batteries and mounts. Nevertheless, this challenging exercise is something that I intend to revisit immediately using various special photo techniques I have in mind and briefly alluded to above.

Yes, Mr. Di Cicco, I am nuts and I painfully have a complete set of incriminating photos from Apollo's paradise to prove it!

About the author

Having successfully managed to retire very early, Anthony Ayiomamitis has now combined his teenage interests of astronomy and photography into a full-time preoccupation and addiction with the astrophotography (film and CCD) of rare, bizarre, extraordinary and challenging extra-terrestrial events. When not in hot pursuit of such eccentric astrophotography projects or touring and imaging ancient Greek ruins and mythical sites, he can be reached through his website Perseus. Of course, with the additional analemmas now in progress, the construction of his home observatory is on-hold yet again for another year!

The analemma pictured at 6h UT was published on APOD on March 20, 2003 as well as in the U.S. "Astronomy Magazine". It was elected "Photo of the year" by the british magazine "Astronomy Now" who published it in its annual calendar 2004. The analemma pictured at 10h UT was published on Spaceweather.com during several days from September 20, 2004, LUXORION receiving the exclusivity for publishing all author's works related to this project.

Ce document est également disponible en français.

For more information

Anthony Ayiomamitis's website (Perseus)

Analemma.com

Steve Irvine

BHM website (in danish)

Jürgen Giesen (sundials and analemma)

David Przewozny (in German)

Analemma on Mars (APOD)

I warmly thanks Anthony Ayiomamitis for his participation.

Page 1 - 2 - 3 - 4 - 5 -


Back to:

HOME

Copyright & FAQ