September 21st was the autumn equinox, which is an important astronomical moment.
This is an opportunity to review some of the basics of the sun's path and in particular to revisit the persistent prejudice that the sun rises in the East and sets in the West.
In reality, it's a bit more complicated than that...
The position of the sun relative to the horizon varies throughout the year, due to the tilt of the Earth's axis of rotation.
The apparent height of the sun above the horizon reaches its minimum at the time of the winter solstice (around December 21) in the Northern Hemisphere and its maximum at the time of the summer solstice (around June 21).
The variation in height will depend on the latitude at which we are located.
To try to better understand the path of the sun, we use heliodons that simulate the sunshine and the path of the sun for a given latitude.
For the purposes of this post, I have therefore modeled a very basic little house that I have placed in a heliodon for the latitude of Lyon (45.75° North).
For the winter solstice (around December 21), we can clearly see that the sun rises near the Southeast and sets in the Southwest (video at the top right).
For the summer solstice (around June 21), we can clearly see that the sun rises almost in the Northeast and sets in the Northwest (video at the bottom right).
Between the winter and summer solstices, which mark the two extremes, the sunset and sunrise of the sun move slightly each day.
After the winter solstice, its course moves towards the North, while it moves towards the South after the summer solstice.
The sun rises precisely in the East and sets in the West only at the equinoxes (around March 21 and September 22), i.e. twice a year (videos in the left column).
Saying that the sun rises in the East and sets in the West is not wrong in itself if we consider the direction in the celestial vault, but it can be misleading.
Strictly speaking, this only happens twice a year.
I have already observed many confusions about the path of the sun and repeating that the sun rises in the East and sets in the West leads to installing stubborn prejudices.
All these variations in the path of the sun have very important consequences in urban planning and architecture for the orientation of buildings, streets and public spaces.
Image: Freio - climatic design