Yesterday I saw Agora, and I was surprised (and pleased) that it had so many references to astronomy.

I knew there were already ancient Greek philosophers speculating about a heliocentric model.
What I didn't know is that they could measure differences in the observed size of the Sun's disk, depending on the time of the year
(and deduce that therefore Earth's orbit must be slightly elliptical).

So that's my question:
without modern instruments, can you really measure the periodic variations in the distance of the Sun due to our elliptical orbit?