Eratosthenes was a Greek scientist who discovered the circumference of the Earth back in 240 B.C. Two TV shows covered his finding. Carl Sagan (Cosmos) shows how he came to the realization that the Earth is curved, and he determined the distance of the circumference.
The next person is Dr. Philip Morrison who did a six part TV show called the Ring of Truth back in 1987. He traveled southward down highway 183 in a van to measure how the star Antares got higher and higher in the sky as he traveled south. This was filmed back in May 1986.
The Earth is curved, and these two men show how it was done, and how you can do it yourself!