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[56.05] Why was the Black Drop Effect so Difficult to See in the 2004 Transit of Venus?

C. Bryja (CCSF), R.D. Sposato (unaffiliated)

We report our Egypt-based observations of Venus transiting the limb of the Sun on 8 June 2004 using a C-5 telescope outfitted with an aperture reduction ring (reducing the diffraction aperture to only three inches) and a Nikon Coolpix 5400 digital camera. We noted various distortions of the image depending upon camera alignment and stability. These distortions resemble some of the sketches made by observers of the 19th-Century transits. Meanwhile, diffraction limited images showed little black drop effect, while the effect became very pronounced during moments of poor seeing. We discuss the causes of the black drop effect and related optical distortions observed during transits, and we comment on the question of why most observers noted little, if any, of these effects during the 2004 transit in contrast to the strong effects reported in previous centuries.

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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.