when you stand on a beach, with your toes in the sea, how far away is the horizon?
it looks further away than it is - because light gets bent
worth asking students to guess first
it is surprisingly near
an exaggerated diagram shows that this is a simple enough application of the pythagoras rule
since the Earth isn't spherical, use the average radius: 6371km
for a 2m (0.002km) eye height the distance is a mere 5.1 km (3 miles)
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