Greg, Just to point out the area of a circle is defined as PI*r^2 or pi*(d^2)/4. Looks like you used the diameter in the formula calling for radius. I had to look it up myself, been a while for me, too. Rick -----Original Message----- From: Greg Askins [mailto:gregaskins@xxxxxxx] Sent: Tuesday, August 26, 2003 6:43 PM To: EVAC@xxxxxxxxxxxxxxxxx; az-observing@xxxxxxxxxxxxx Subject: [AZ-Observing] Some Mars Figuring (while waiting for clear skies!)... While waiting for the skies to get dark (and hopefully get/stay clear) to view Mars this week, I started wondering just how much larger Mars is this week than it will be over the next few weeks (as our weather here in Phoenix should start to get better). Looking through my recent Sky&Telescopes and Astronomy magazines, I was surprised how much smaller Mars was depicted by the end of September (even though its diamater measurement was still almost 85% of maximum). With some time on my hands (since the observing here has been difficult and doesn't look great tonight during the evening hours), I decided to calculate the total viewable size of Mars (its total area) including the effect of its upcoming phase. Using the data supplied here by EVAC: http://www.eastvalleyastronomy.org/EVAC/mars-ephem03.htm I get a total size of Mars at maximum of 494.214 square arc-seconds (I think this is the proper notation). I used this equation: (25.11/2)squared X 3.1416 X .998 phase. Now for the comparisons (% of Max. Size and Total Size -- including phase effect): Maximum (8/27/03): (100%) 494.214 sq.arc-secs One month later 9/27/03: (69.7%) 344.537 sq.arc-secs Star party on 10/01/03: (64.1%) 316.910 sq.arc-secs Star party on 10/03/03: (61.3%) 303.127 sq.arc-secs Star party on 10/10/03: (52.4%) 258.985 sq.arc-secs Middle of Oct. 10/15/03: (46.7%) 230.743 sq.arc-secs This total size measurement should be important both for astro-imaging and for the overall impressiveness of Mars in the eyepiece. Somewhat surprisingly, by the end of September, Mars will be at less than 2/3rds of it's maximum size tonight -- and before the middle of October will be at less than 50% of maximum. Morale of the story: pray for some clear skies the next two weeks! Greg Askins Chandler, AZ P.S. If there are mistakes in my math, I apologize -- it's been a while! -- See message header for info on list archives or unsubscribing, and please send personal replies to the author, not the list. -- See message header for info on list archives or unsubscribing, and please send personal replies to the author, not the list.