Read More: The Conversation
You cannot feel or hear the world turning. It does not rumble through space. But you can see it turn with your own eyes every day and night. And, with patience, you can see Earth travel around the Sun. As the globe turns and night falls, stars appear to travel from east to west across the night sky. Or do they? How stars move across the sky is a touch more complicated than you may first imagine. And the motion of the stars tells us about our place on the world and our travels around the Sun. We live on a spinning globe, and as we turn different swathes of the universe come into view. However, what you see depends on where you are. Guiding light Almost directly above the North Pole is the star Polaris. As the world turns on its axis, Polaris remains above the North Pole. If you had the misfortune of being at the North Pole in midwinter, Polaris would be a constant companion overhead. Imagine an alien looking down from Polaris at Earth. What would they see? They would see Earth’s Northern Hemisphere, spinning anticlockwise around the North Pole. A Polarisian would never see Earth’s Southern Hemisphere, with its red Australian deserts and frozen Antarctic wastes. Who can see Polaris from Earth? People across the Northern Hemisphere can see Polaris, and it never rises nor sets. However, while Polaris is high in the sky when viewed from inside the Arctic circle, as you move towards the Equator, Polaris gets closer and closer to the northern horizon. If you travel into the Southern Hemisphere, Polaris falls below the northern horizon, and never rises at all. So which stars you see and how high they get in the sky depends on where you are. Indeed, navigators have used the stars for centuries to determine how far they are from the Equator.