On Mercury, the Sun can rise... then turn back

The first part of the sun appears on the horizon. Then he goes back down, before getting up again. This spectacle would be possible from certain regions of Mercury: the apparent movement of our star there experiences an interruption that our earthly mornings have not taught us.

The planet rotates slowly on itself, in about fifty-nine Earth days, while following a very elliptical orbit. When it passes closer to the Sun, its orbital speed increases enough to temporarily change the direction of movement of the Sun in its sky. It is the two combined movements that produce this apparent return.

The phenomenon does not present itself in the same way everywhere. Nor does it mean that the Sun actually changes direction in space. To understand this hesitant morning, we must look at the ground that turns under the observer and the trajectory that prevails. On Mercury, seeing the day begin does not guarantee that it will continue immediately.