Paul Eska, age 11, of Sayreville, N.J., for his question:

Who first measured the earth's circumference?

As far as we know, the first person to estimate the distance around the globe was Eratosthenes of ancient Alexandria.    To work out his complex geometry problem, he used the noonday shadows made on the longest day of the year.

At the town of Syene, some 500 miles due south of Alexandria, the noonday midsummer sun was known to be directly overhead. At the same moment, in Alexandria the sun cast a shadow with a measurable angle. Eratosthenes computed the shadow angles with the distance between the two cities to estimate the total circumference of the globe. He performed this measuring miracle around 250 B.C.  and his answer was almost correct.