À propos du soleil de ptaff.ca/Description (english)

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Sunrise and sunset

The selected definition of the sunrise/sunset is the moment with the superior arc of the sun is 35 minutes of arc (0,582°) below the horizon. This 35 minutes of arc is the estimation of the refraction effect of the atmosphere. It is though to be constant for any place on Earth, all year long.

When it is the case, the changes caused by summer time is used. Those are the discontinuities that are seen on the curves for sunrise and sunset.

The time of light is the time spend between the sunrise and the sunset.

Daily variation of time of light

This graphic shows the gain or lost of time of light in minutes, compare to the day before.

Maximal sun altitude

This is the maximum altitude, in degrees, reach by the sun each day. The overall maximum altitude is 90° and corresponds to the zenith and is only reach by the places in the tropics.

During the polar night, the value of 0 is used.

Daily maximal solar flux

The daily maximal solar flux correspond to the maximal quantity of energy per unit of surface receive from the sun for a given place. The unit used is the watt per square meter.

The maximal flux happens when the sun is at its maximal altitude in the sky. This is a theoretical value computed from the equations of the physical library of the atmospherical model of Environment Canada. Those equations are the same that are used in the model for the forecast of temperature of the roads METRo.

Twilight length

The twilight is the time between dawn and sunrise, and the time between sunset and dusk.

The twilight length is computed by using the time between the sunset/sunrise and the moment when the sun is 12° below the horizon. This is the definition of the nautical twilight. Hence, there are 2 twilight every day, one at sunrise and one at sunset. This is the sum of those 2 values that is given.

The nautical twilight had been chosen because it is at this moment that we can see the first light of the sun.