User:Syncategoremata/Pre-telescopic observations of the transit of Mercury and Venus

There are various claims for pre-telescopic observations of transits of Venus and Mercury. Transits of Mercury cannot be be observed without a telescope.

"It is interesting to note that in connection with the transit of Venus he [that is, Abū Ṭālib] mentions the name of Quṭbuddīn Shīrāzī (1236–1311), to whom it was known. We know today that Ibn Sīnā (d. 1073), Ibn Bājja (d. 1138) and others had observed 'the two planets as black spots on the face of the sun', [n26] evidently due to the transit(s) of Venus and/or Mercury. In fact Quṭbuddīn has referred to the observation of the Venus transit by Ibn Bājja. [n27].", p. 137

n26. Sayili (1958), p.360, esp. f.n. 24.

n27. Goldstein (1969), esp. p. 55.

Sayili (1958) is "Islam and the Rise of Seventeenth Century Science", Belleten (Ankara), Vol. 22, no. 87, July Issues, pp. 353–368

Transits of Mercury

In a study of naked-eye sunspot visibility, it was determined that the lower limit for visibility was an overall apparent diameter of 19.3″. At its greatest, the apparent diameter of Mercury is just 13″ and so its transits would not be visible to the naked eye.

Most if not all pre-telescopic observations of transits were of sunspots

Sunspot observations during the Aristotelian period would have been taken to be observations of planets as Aristotelian doctrine was that the sun was immaculate and not subject to change. Assuming that the text is not corrupt, this can be seen at work in the observations of 807 of a spot on the sun for a period of 8 days. Any transit of Mercury would last no longer than 6 hours and yet this event was still described as a transit.