Copernicus reports a period of visibility for Venus that is a month and half longer than what we observe today. A century or so after Copernicus, we have another similar timing discrepancy for observation of the visibility of Venus that relates to Galileo:

“First of all, when did Galileo begin to observe Venus? On one hand, Galileo told Clavius that he had started his observations “when Venus began to be visible in the evening sky”. On the other hand, he told Castelli that he had started his observations about three months earlier, that is, at the beginning of October. But is clear that “when Venus began to be visible in the evening sky” cannot coincide with the beginning of October.”

[articles.adsabs.harvard.edu]

- Laird



Edited 2 time(s). Last edit at 31-Oct-15 18:58 by Laird Scranton.