2013/11/07 by Kevin Krisciunas, K. Krisciunas, Krisciunas, Kevin
Arts and Humanities · Physics and Astronomy · Social Sciences · #Ancient Egypt and Archaeology #FOS: Physical sciences #Historical Astronomy and Related Studies #Historical Geography and Cartography #Historical and Architectural Studies #History and Philosophy of Physics (physics.hist-ph) #Popular Physics (physics.pop-ph) #physics.hist-ph #physics.pop-ph
paper · pdf · doi:10.48550/arxiv.1311.2798
10 pages, 4 figures; to be published in Asian Journal of Physics
arxiv created 2013/11/07 · openalex publication_date 2013/11/07 · arxiv updated 2013/11/13 · openalex created_date 2022/09/01 · openalex updated_date 2026/07/28
Ptolemy's model of the Moon's motion implied that its distance varies by nearly a factor of two, implying that its angular size should also vary by nearly a factor of two. We present an analysis of 100 naked eye observations of the Moon's angular size obtained over 1145 days, showing regular variations of at least 3 arc minutes. Thus, ancient astronomers could have shown that a key implication of Ptolemy's model was wrong. In modern times we attribute the variation of distance of the Moon to the combined effect of the ellipticity of the Moon's orbit and the perturbing effect of the Sun on the Earth-Moon system. We show graphically how this affects the ecliptic longitudes and radial distance of the Moon. The longitude and distance "anomalies" are correlated with the Moon's phase. This is illustrated without any complex equations or geometry.