ocr: A: time series of 6 images of comet Hale-Bopp taken by the SWAN instrument on board SOHO in the ul- traviolet light (1100-1800, A), on. January 4, February 2 and 18, March 4 and 16, and April 3, 1997,as the comet slowly approaches the Sun. Hale-Bopp is clearly visible because of its huge hydrogen cloud produced by phofo-dissociation of water vapor molecules evaporated from the solid nucleus.
