To photograph the sunset on the Grand Canal in Versailles - 2009-04-06
To photograph the sunset on the Grand Canal in Versailles
One reads sometimes in some journals that the axes of the Grand canal of the palace of Versailles are orientated East-West and North-South. Some deduced, with good reason, that the Sun was to lie down in the axis of the Grand canal at the equinoxes.

However the azimuth of the axis is not perfectly orientated East-West, it deviates from approximately 22° what changes considerably the dates when this phenomenon is observable. The altitude of the floor in front of the frontage of the palace of Versailles turned towards the Grand canal is 142m. The horizon in the direction of the Grand canal is heightened because of a hill of 128 meters altitude, located at 10650 meters.

The azimuth of the axis of the Grand canal is 111°49' 56 " , thus approximately 111°50 '; (approximately 292 ° northern). Taking into account the atmospheric refraction and these various parameters, we calculated that the center of the Sun lies down in 2008 in the axis of the Grand canal at the following dates:

Sunset in the axis of the Grand Canal Hour of sunset (TLF)*Azimuth
The 26th april 2009 20h 55min 26s111° 22' 58"
The 27th april 2009 20h 56min 54s111° 53' 14"
The 28th april 2009 20h 58min 21s112° 23' 11"
* TLF = French legal time

More details:
Be cautious: if the horizon is badly estimated, these results can be shifted by one day or two. The same if one goes up in altitude, for example if one observes from the first floor of the castle, the results can also be shifted by one day.

Moreover these calculations were made with a certain value of the horizontal atmospheric refraction, but the refraction varies with the atmospheric conditions (pressure, temperature...) the times of the sunsets can thus vary slightly with respect to the predicted values.

We gave these values to the nearest second of time but it is only the internal precision of calculation, the precision of the prediction, taking into account the uncertainties on the refraction, is about one minute of time.

If one studies the data above, one notes that the azimuth of the center of the Sun at sunset never falls exactly into the axis from the channel, it is close to this axis for the median dates (on April 27 and on August 14), it is slightly to the south (towards the left) when the azimuth is lower than 111°49' 56 "and slightly to the north (towards the right) when the azimuth is higher than 111°49' 56".

In all the cases it is possible to take a photograph in the axis of the Grand canal but the center of the Sun will be more or less high with respect to the horizon. One can also exploit the height of the observer while going down or while going up compared to the terrace of the frontage. If one goes up, the center of the Sun will be higher, if one goes down, the center of the Sun will be lower.

Caution: If the Sun at sunset dazzles you, do not look at it directly: it is still too high on the horizon. In this case prevent photographing it without filter, you are likely to damage your camera and your sight if you use an apparatus with a reflex optics.

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