A shadow over Oxie: an October 2003 amateur observation of HD 209458b

This paper describes a photometry observation by an amateur astronomer of a transit of the extrasolar planet HD 209458b across its star on the 26th of October 2003. A description of the telescope, CCD imager, software and method used is provided. The preparations leading to the transit observation are described, along with a chronology. The results of the observation (in the form of a time-magnitude diagram) is reproduced, investigated and discussed. It is concluded that the HD 209458b transit most probably was observed. A number of less successful attempts at observing HD 209458b transits in August and October 2003 are also described. A general introduction describes the development in astronomy leading to observations of extrasolar planets in general and amateur observations of extrasolar planets in particular.