magnitude limits of telescopes

As I was reviewing my things-I'd-like-to-do-astronomically list, on noting that I want to re-observe the moons of Uranus and Neptune, I suddenly thought, hey, I should add the moons of Mars. But then I wondered, is that even possible?

Did a couple of quick searches via Yahoo! but didn't turn up any leads.

Fired up Stellarium, went to Mars, clicked on the moons, and saw that they were presenting at magnitudes 14.something. Oh. Nasty. That's at the edge of visibility for my Celestron 8" Schmidt-Cassegrain telescope in dark skies (under visual use). I know 14 is the limit based on remarks I read (and memorised) a long time ago in All About Telescopes. But then I wondered what the limit of the RASC Toronto Centre's C14 was.

Not having my bootleg AAT sheets handy (man, I gotta buy that book!), I web-searched "limiting magnitude" and stumbled into the Woodland Hills Camera and Telescopes site and the Telescope Science page on aperture. Ah ha. Found the formula:

limiting visual magnitude
= 2.7 + 5 * log-base-10 of aperture (in mm)

So, I crunched the numbers for 'scopes I get to look through...

• 12.4 - the Questar
• 12.7 - CAO Tele Vue 101
• 13.6 - Mom's newt
• 14.2 - my 8"
• 15.5 - C14!
• (and, out of curiousity, 15.6 in Phil's Obsession)
  

Awesome. That means that Mars's small moons are accessible in the Centre's telescope on Blue Mountain.

Hold the phone. Jumped back into Stellarium and started tapping the ] key, to advance one week. And watched the planet get bigger... March 2012 I stopped. That is the best time in the next apparition of Mars, when the Red Planet is closest to the Earth. Checked the magnitudes of the moons again: oh, ho! Mag 12! Very doable.

Rather handy, knowing that formula.

§

Updated the CAO eyepiece-telescope matrix spreadsheet (and uploaded it). And I updated the "our telescopes" sheet in my Psion for Mom's and my OTAs.