Observation du Canigou aux environs de Marseille le 4 fevrier 2011

(English explanation at bottom)
Vidéo accélérée 2 fois.
Observation du massif du Canigou (2785m) depuis les environs de Marseille le 4 février 2011. Cette observation montre qu'il est possible d'observer ce sommet des Pyrénées distant de près de 250km.
Ce phénomène lié à la réfraction atmosphérique est aussi un phénomène astronomique puisqu'il s'agit d'un alignement avec le Soleil au couchant. Il est observable à deux périodes chaque année, février et octobre.
Pour connaitre toutes les dates d'observation ainsi que les lieux correspondants depuis Toulon jusqu'à Salon consulter le site d'Alain Origné mis à jour régulièrement:
http://canigou.allauch.free.fr

ENGLISH :
Accelerated video twice.
Observation of Canigou (2785m/8400ft) from a place near Marseille (south France) February 4, 2011. This observation shows that it is possible to observe the Canigou, summit of the Pyrenees at a distance of 253km/157miles in straight line over the mediterranean sea.
The atmospheric refraction, well kown by astronomers as astronomical refraction for extraterrestial objects like Sun Moon and stars, makes possible this observation of this rare phenomenon. This refraction lifts far objects such as mountain peaks above the horizon.The continuous variation of the pressure from sea level to the top of the atmosphere bends the path of the light which is gently curved over the horizon.
Also high contrast between mountain and backgound of the sky is required to see clearly the phenomenon because of the attenuation of the light during long travel through the atmosphere. The high contrast can be obtain when the Sun is aligned with the mountaint. In this case this phenomenon can be seen at two periods each year, around the 10th february and 3st October. Sometime in anticyclonic conditions, with perfectly clear atmosphere and low temperature, the Canigou mountain can also be observed without the need of an astronomical alignment with the Sun or Moon.