Round Earth/Flat Earth 1/7/15 1.How do we know the Earth is round? 2.We will use models and simulations to show how sailing ships and shadows are evidence for a round Earth. NOTES: Horizon- Where the sky and Earth appear to meet Line of Sight- The straight path taken by light from an object to an eye The length of a shadow depends on the angle of incoming light Shadow length varies depending on latitude (the further north you go, the shadows get longer because sunlight is not as direct)

For centuries ships sailed the open seas carrying materials and goods like metals, food, and household products from port to port. Merchants on shore waiting for the next delivery from sea would often observe the arriving ship rise out of the sea, first the top of the sail, then the main sail, and finally the deck and hull. The same observers would report that the ship sailing from port seemed to sink into the sea, disappearing below the surface until just the top sail was visible. They might well have wondered why this happened. The sailors on board the ship also logged interesting reports. Sailors always kept constant lookout in all directions and from all locations on a ship at sea, watching for dangers and for land. Interestingly enough, it was always the sailor up in the crow's nest near the top of the mast who sighted land first. The sailors on deck would stare in vain for their first glimpse of land. It would be several minutes before land would heave into view for the crew on deck. Why did the lookout in the crow's nest always spy land first? Just luck?

Line of Sight

Eratosthenes- great Greek mathematician who determined the circumference (distance around) the Earth using shadow observations.