French astronomer Michel Giacobini (1873 - 1938) discovered comet 205P/Giacobini on September 4, 1896, but it was not seen on its return, a little less than 7 years later, and was considered a lost comet and consequently designated D/1896 R2. On September 10, 2008, amateur supernova hunters Koichi Itagaki and Hiroshi Kaneda rediscovered it, on its seventeenth return. Source