Charly, My understanding is that the 25mag/arcsec is very close to the background sky glow and just a measure of brightness. What they are trying to say, is that the galaxy, at the limiting magnitude of the sky, has a maximum size equal to the "major axis diameter" quoted. Usually magnitudes of galaxies/ nebulae etc are given in cataalogues as a total integrated magnitude i.e. as if all the light from the galaxy was condensed down to a star like image. There are some "standard surface brightness" calculations I've seen somewhere, which are used for fainter galaxies to give an estimate of their size, but very academic.
2008/7/2 klauslms <[EMAIL PROTECTED]>: > Hello all! > Is someone so kind and explain what major axis diameter at > 25mag/arcsec2 (from PGC catalogue) means and if there is a connection > to magnitude and size of the objekt and how to compute this? > Kind regards > Charly > > > [Non-text portions of this message have been removed]
