of the Julian calendar. (From an article in the February 1, 2005 Astrophysical Journal by D. L. Buzasi et al.) Read Vega , Deneb and Altair 's entries in Wikipedia. Comet C/2006 M4 ( SWAN ) Discovery Date June 20, 2006 Magnitude 12 mag Discoverer R. D. Matson (Irvine, CA), M.