Hello all, I have found very interesting the note of Anselmo Perez Serrada concerning the sunset seen through the Arc de Triompe in Paris and the images communicated by Jean-Paul Cornec and particularly #3 (http://acdsweb.free.fr/evenements/rayon_vert/diapo/vue16.html) and #1 (http://www.astrosurf.com/poisaya/astro/planetaire/08triomphesoleil.htm).
To find the characteristics of the phenomenon I have tried to make some "gnomonic" calculations . Knowing the Latitude, the Longitude, the day and the dimensions of the Arc de Triompe, I have found that in the instant in which the photo #3 was taken the Sun had an Azimuth = 117.7 degrees, its center had an altitude slightly inferior of 45' and the hour was 21h 12m 30s (in France in May it is in force the saving time). The photographer was at a distance of around 1210m from the front of the arc. The photo #1 probably was taken on May 10; in it the Sun has an altitude of around 22-23' and the inferior edge is at only 7' above the horizon; the distance of the photographer is slightly superior (around 1230m). This value of the azimuth is obviously also the azimuth of the avenue of the Champs Elysee if the photographer was exactly on the centre line of the avenue. Since the width of the Champs is very great (around 60 m) the photographer could be moved from the centre line of 20m or more : for this reason the value of the Azimuth of the avenue could differ from the Sun's Azimuth also for ±1°. Knowing the Azimuth of the avenue is easy to find the instants in which the phenomenon will be repeated and its characteristics. Taking the value of 117.7° and supposing to be at around 1200m from the arc, we find that in 2003 the phenomenon will be visible on the following days : 5/10/2003 s 21h 14m a = 18 ' the sun has the lower limb almost on the horizon 5/11/2003 S 21h 13m a = 35 ' the sun is centered in the arc 5/12/2003 m 21h 12m a = 51 ' the sun touches the superior edge of the arc 7/31/2003 t 21h 22m a = 54 ' 8/01/2003 f 21h 23m a = 37 ' 8/02/2003 s 20h 24m a = 21 ' 8/03/2003 S 21h 25m a = 4.5 ' the sun is already partly set Obviously if the photographer comes near the arc, the apparent diameter of the arc itself becomes greater then the Sun and the phenomenon can be seen probably also in other days. For example going at the distance of around 750m the width of the arc is double of the Sun's diameter. The maximum distance to see the whole Sun's disk is 1500m . If the azimuth of the avenue is slightly different we can have changes of some minutes: in a minute the Sun' center moves of around 11.3' in Azimuth and -7.5' in altitude. The phenomenon would be visible in the Champs Elysee even if the Azimuth of the avenue had a value between 53° and 127°: these numbers well explain the reason for which this phenomenon has to be very common, as also Anselmo writes . For example for a place with Latitude = 40° we can the Sun set exactly on the center line of a street, or of other alignment, if this has an Azimuth between 59° and 122° . I hope that Mike Shaw find a cloudless weather and send us a photo and the data of the event , when he will go in Paris next spring :-) Best regards, Gianni Ferrari 44° 39' N 10° 55' E Mailto : [EMAIL PROTECTED] -
