One Day on Two Orbits is a permanent floor sculpture by Nadia Kaabi-Linke that shows the shadows of a bicycle on the ground over the course of one day, following the gradual transition from day to night, from the sun to the moon. While the bicycle itself is invisible, the shape of the revolving shadow forms an image reminiscent of astronomical photographs of distant galaxies.The work pays homage to Ibn al-Haytham, who introduced the idea that the sun and the moon revolve on geometrically and temporally different orbits. This discovery led to a better understanding of both space and time on Earth and explained the existence of two calendar systems. One Day on Two Orbits is a memorial for a celestial discovery that not only relocated the Earth in the solar system, but also harmonised different cultures of time.