Brightness of extended objects (Planets)

[Macavity]

Brightness of extended objects (Planets): Since purchase of a (quite reasonable for it's intent!) Orion "Solar System Colour Imager", one aspect continues to intrigue...

As many will know these CMOS-based webcams are for imaging the "brighter planets". Personally, I have used mine for imaging the Moon and (filtered) Sun. But what of brightness for extended planetary etc. disks? Can one calculate brightness per pixel from magnitude, angular diameter etc. Not something I NEED to know... just curious!

On the face of it, and the back of an envelope calculation, Mars might actually be a "brighter" (per pixel) planet than Jupiter etc.

[dph1nm]

Yes, you can, although to do it properly you would have to worry about limb darkening etc.

Basically if your image of apparent magnitude m covers n pixels, then the magnitude per pixel is simply m+2.5*log10(n). It is more usual to quote such surface brightnesses in magnitude per square arcsec, which you can calculate in similar fashion if you know the area of a pixel in sq. arcsec.

NigelM