In a Cloudy Night's forum, someone pointed out that you can use the Google search box's built-in calculator to find the physical size of Comet 17P. In general - sin ( radians (your_arcmins arcmins) ) * 1.62900 [a.u.] * 149 597 871 = physical size 17P Get the current day's distance to Comet 17P from the NASA-JPL Near Earth Object orbit simulator - http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=17P&orb=1 An example of a string that is formated for use in the Google search box is: sin(radians * (10 arcminutes)) * 1.62900 * 149 597 871 which yields = 708 878.821 kilometers According to Allen's Astrophysical Quantities, typical comet coma physical diameters are 10,000 to 100,000 km. - Kurt Updated to Utah astro wiki current events _______________________________________________ Sent via CSolutions - http://www.csolutions.net