http://articles.adsabs.harvard.edu/full/seri/JBAA./0111//0000266.000.html

For the Aristarchus method of determining the Earth-Sun distance, 3º corresponds to ~0.77 arcminutes as seen by the observer on Earth (the deviation from true straightness of the terminator). An observer at a single point on the Earth’s surface would never be able to observe the moon around first quarter over the length of time required to interpolate between ±3º because this would take 12 hours and the maximum observing time would be no more than half of this (from moon on eastern horizon and sun at zenith to moon at zenith and sun on western horizon). Hence one could never correct for the systematic error of taking the first measurement where the terminator appeared straight. [1]

[1] In theory one could if the observer was at the North Pole and the measurement was made in mid-summer; however all these measurements were made at mid-latitudes.

]]>1) Did you ever write a post on the discovery that the “fixed stars” are not actually fixed? If yes, can you link it to me? If not, do you think you’ll write that in the future (maybe even in this series)?

2) Which book would you recommend on the history of geometrical optic to someone interested in it? ]]>

Good idea. I certainly wouldn’t recommend spending money on this one.

]]>Looks interesting but too expensive to buy. Will see if I can get hold of a copy though interlibrary loan

]]>Kronecker Wallis offer quite a lot of interesting facsimiles

]]>Euclid’s proof that there is no largest prime is one of my favourite mathematical proofs

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