When we talk about the reason for the seasons, we usually have to dispel the misconception that seasons are caused by being close and far away in the Earth's elliptical orbit.

And usually, we mention that the Earth is actually closest to the sun in January, in the dead of winter (for the Northern hemisphere).

But when did astronomers first have the Earth's orbit measured carefully enough that they knew the Earth was slightly closer during January? How was that measurement made? How accurate were the first measurements?

They didn't they measure the size of the disk of the sun very, very carefully, did they? Perhaps with a pin-hole camera? That seems like it would be very difficult to do.

I guess if we are talking about long enough ago, they would have thought it was the Sun's orbit that brought it closer because either because of an eccentric (the idea that the orbit of an ancient planet had a center that was offset) or because of epicycles bringing the Sun closer on the circle on a circle.

I just wonder what sort of observation they might have made.

One of the nicest comparisons I've seen can be found here.

If it was me with the tools available in ancient times, I'd probably use a rotatable camera obscura, and maybe a cone with markings to place at the center of the image of the sun, to exaggerate the effect of the size differences.