Growing up as a JW, I always thought the ancients were scientific morons who knew next to nothing. Ashamedly, I used to run around citing Isaiah 40:22 as proof of the Bible's 'divine authorship' because it talked about "the circle of the earth". As though this were somehow an unknowable before spaceflight.
But the more I learn about history, the more I realize just how advanced some of the Ancients were. Eratosthenes calculating the diameter of the earth has been referenced in several threads on this site. But someone you may never of heard of is Aristarchus.
Not a whole lot is know about him but in the year 200 BC Aristarchus' contemporary, Archimedes, wrote a fascinating book called The Sand Reckoner in which Archimedes attempted to calculate how many grains of sand could fit inside the universe. Using parallax and a few assumptions, Archimedes figured the universe was about 2 light years across (pretty astounding for a man of antiquity).
But even more interesting than Archimedes estimations, is his reference to a man who was putting forth the heliocentric model some 1,800 years before Copernicus formalized and popularized the idea. Here's a passage from Archimedes book:
You are now aware that the "universe" is the name given by most astronomers to the sphere the center of which is the center of the earth, while its radius is equal to the straight line between the center of the sun and the center of the earth. This is the common account as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the "universe" just mentioned. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same center as the sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.
Sadly, Aristarchus own writings were lost when the Christians burned down and raised the Library of Alexandria. It kinda makes me wonder what else the ancients knew.