Reloj analemático de Alfambra
LOCATION
The analemmatic sundial of Alfambra, built in 2006, is located next to the hermitage of Santa Ana, 6.5 kilometres from the town in the direction of Santa Eulalia.
DESCRIPCION
The Alfambra analemmatic sundial is the first analemmatic sundial to be built in Aragon and one of the largest in Spain. It has an external diameter of more than 15 metres and is made of pink granite. The coats of arms of the military orders that have passed through Alfambra throughout its history are represented on it: the orders of Monte Gaudio, the Holy Redeemer, the Temple, Montesa, Jerusalem and Malta.
The clock consists of an ellipse on which the hours of the day in sunlight (from 6 a.m. to 10 p.m.) are printed. The major axis of the ellipse measures 8 metres and is oriented East-West. The minor axis is about 4 metres long and is oriented North-South. The length of the major axis is free: it depends on the place where the clock is to be built. To obtain the dimension of the minor axis, a formula is used that takes into account the size of the major axis and the latitude of the place where the clock is to be built.
In the centre of the ellipse we find the analemma, a figure of eight or infinity symbol, in which the twelve months of the year are located, divided into periods of ten days. The analemma is the curve that describes the position of the Sun in the sky, if we observe it every day of the year at the same time of day and from the same place of observation.
To better understand how an analemma is obtained, let us imagine that we take a photograph of the Sun every day at the same time from the same point. Will the Sun always be in the same position? The answer is no. We all know that the Sun rises in the East and sets in the West, but, in reality, only twice a year the Sun rises just in the East and sets just in the West: these are the days corresponding to the vernal (21 March) and autumnal (21 September) equinoxes. During spring and summer the Sun moves from north-east to north-west, while in autumn and winter it moves from south-west to south-east, reaching the extreme trajectories at the summer solstice (northernmost point of the analemma) and winter solstice (southernmost point of the analemma). This observed displacement is due to the motion of the Earth around the Sun (which does not follow a circular but an elliptical path) and to the tilt of the Earth’s axis of rotation.
The observation of this phenomenon is simple. We must fix a point of observation of the Sun (a window of a house facing east, for example). We must pay attention to the place on the horizon where the Sun rises. Let us suppose that we start the observation on 21 March (the vernal equinox). Between that day and 21 June, the Sun is moving northwards, so if we look at it from the front it will move to the left. It will reach its most northerly point on 21 June (summer solstice). If we follow the observation we will see that the sunrise starts to move southwards. Just on September 21st (autumnal equinox) the sunrise coincides with the cardinal point East. This is the same place where it rose on 21 March. From that day onwards the rising point will continue to move southwards (to our right if we are facing east) and will continue in that direction until it reaches the southernmost point on 21 December (winter solstice). It will then begin to return to the east until it completes its annual cycle on 21 March (the vernal equinox).
This phenomenon explains why our shadow, at the same time but on different days, does not have the same size or the same orientation. However, it is important to know that at solar noon, our shadow always faces just north. This happens every day and is a very interesting fact. It is the time when the Sun is at the highest point of its apparent path.