Caption: An imaginative portrait of William Crabtree (1610--1644) observing the 1639 transit of Venus (1639 Dec04).

Features:

1. This and the observation done nearly simultaneously in another location by Crabtree's friend Jeremiah Horrocks (1618--1641) were the first observations ever of a transit of Venus---the passage of Venus across the face of Sun (i.e., the solar photosphere).

2. The observational setup is NOT entirely clear to yours truly. But it seems to be pinhole projection using a telescope with NO eyepiece. The setup allowed the image created by the primary to be focused onto a screen. Benedetto Castelli (1578--1643) seems to have invented pinhole projection with a telescope in 1612 (see Galileo Project: Science: Sunspots: scroll down ∼ 40 %).

   Simple pinhole projection can be used too, but using a telescope collects more sunlight and allows a brighter image to be created.

   Crabtree's setup or just pinhole projection without a telescope can also be used observe sunspots.

3. The painter Ford Madox Brown (1821--1893) seems to think he was doing a Dutch genre painting---"The astronomer in nightgown with his family in his study observing the transit of Venus".

4. Transits of Venus (i.e., transits of Venus ♀ across the solar photosphere) usually occur in pairs separated by 8 years twice in a period of nearly 243 years. The pattern to good accuracy/precision is:
   1. Time zero of the cycle.
   2. 105.5 years later, the first of a pair (105.5 years from time zero).
   3. 8 years later, the second of the pair (113.5 years from time zero).
   4. 121.5 years later, the first a new pair (235.0 years from time zero).
   5. 8 years later, the second of the new pair (243.0 years from time zero).
   6. And then the cycle repeats just has it as done since long before ancient Babylonian astronomy (c.1830--c.60 BCE) and will for ages to come.

   The last pair of Venus transits were in years 2004 and 2012 and the next pair will be in 2117 and 2125. See Wikipedia: Transit of Venus: Past and future transits.