Illustration of Archimedes' ([i]Sand Reckoner[/i], 1.10-1.16) measurement of the Sun's angular size.

In [i]The Sand Reckoner[/i] (1.10–1.16), Archimedes describes how he measured the Sun's angular size.[br]Place the cylinders either close to or far from the target (leftmost point). Follow Archimedes' instructions (as shown in the illustration), and you will also find upper and lower bounds for the Sun's angular size. For illustrative purposes, this has been set to about 20 degrees here, whereas the actual value is 0.5 degrees. For more realistic settings, make [i]R[/i] one-tenth of a mm larger than [i]r[/i] and set the distance [i]d[/i] between the cylinders to approximately 22.8825 mm.