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J.T.T. Mäkinen (Finnish Meteorological Institute), J.L. Bertaux (Service d'Aeronomie), T.I. Pulkkinen, W. Schmidth, E. Kyrölä, T. Summanen (Finnish Meteorological Institute), E. Quemerais, R. Lallement (Service d'Aeronomie)
The SWAN instrument onboard the SOHO spacecraft is a Lyman \alpha scanning photometer cabable of mapping the whole sky with 1\deg resolution. Since January 1996 the instrument has produced about three full sky maps a week with the principal scientific objective of observing the distribution of heliospheric neutral hydrogen. Despite the coarse resolution the instrument is an excellent tool for systematic observations of comets down to a visual magnitude of about 12, which was demonstrated by the discovery of C/1997 K2 , and for determining their water production rate as a function of time. Here we present the latest results from the SWAN cometary observations.
 Mäkinen, T. et al. Discovery of a comet by its Lyman-\alpha emission, Nature 405, 321-322 (2000).