Reports from Geisei Observatory <June 12, 2010>

Photograph of C/2009 R1 (McNaught)

　　　　This is an observation of C/2009 R1 (McNaught), which is gradually brightening in the predawn sky. I observed the comet at 3 am on June 9, although the near last-quarter moon was in the sky. The total photographic magnitude is 5.4 and the coma is 3' in diameter. Even if its low altitude in the predawn sky is taken into account, its appearance was somewhat less than expected of a naked-eye comet. It was barely detectable in a 7x50 finderscope. The image by the 70cm telescope with a Nikon D700 shows a beautiful blue coma trailing a short tail. There is a 15'-long reddish dust tail at PA 280°and a 10'-long blue ion tail is seen at PA 260°. A tiny white nucleus is visible at the dead center of the blue coma. It may brighten to 3.5 to 3.9 magnitude at the best around its perihelion on July 2nd.