In Mercury's sky, the Sun sometimes loops backwards. If this happens at sunrise, as seen here, you have the curious spectacle of a double dawn. It occurs because of the way Mercury turns very slowly while following its elliptical orbit round the Sun.
A mercurian 'day', lasts 176 Earth days, equivalent to two mercurian 'years'. Because Mercury's orbit is rather elliptical, the planet's distance from the Sun and its speed of travel both vary substantially over the course of one orbit. These things together cause the strange motion of the Sun in the sky.
