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# by rough estimates
from the bits we see and galaxy models. 10 billion stars with absolute magnitude of about 2 each gives such and so much luminosity. a calculation like that based on the mass of the milky way and some model of star formation rates.

at least that's how i'd do it. some retard probably just put a random number into wikipedia though...
(I helped save b3ta! boris the spider, Sat 10 May 2008, 22:28, archived)
# you'd still need to be only about 1000 light years from the Milky Way
for it to be as bright as the Moon though, which would still be inside the bulge.
(I helped save b3ta! Moon Girl Technologies horrendous beanbag, Sat 10 May 2008, 22:34, archived)
# yeah that's what i meant by
"to be far enough away to get that kind of view it'd be a bit fainter". personally i don't feel that the absolute magnitude of a galaxy has anything more than a formal meaning.

also from sources i trust a bit more than wikipedia, both rigel and deneb have an absolute magnitude of -7.1 so i'd be astonished if a galaxy was that dim. moreover, supernova ia can be around -19 or so, and rival galaxies. i'd guess the whirlpool might be -17 or so?
(I helped save b3ta! boris the spider, Sat 10 May 2008, 22:37, archived)
# I don't suppose it's simply additive though,
and of course it's logarithmic as well. And there's a lot of light-absorbing dust floating around inside a galaxy.
Another reason they look so faint is that the light is coming from an extended object, rather than a point source; the light is all spread out.
(I helped save b3ta! Moon Girl Technologies horrendous beanbag, Sat 10 May 2008, 22:38, archived)
# no it's not additive
simply because it's logarithmic. also if we're being picky about actually being 10pc from a galaxy, whatever that means, you've got the problem that there's no way you'll ever see the whole galaxy at teh same time, rendering an absolute magnitude physically meaningless.

even so, i really don't believe it's got an absolute magnitude -- no matter how little that might mean of only -7....

but it's hardly important enough to dick around with.

i've now got "mmmbop" playing on my telly with german subtitles. this is simply weird. they've even subtitled "MMMbop tick a top a ba do bop" and so on.




edit: the picture's nicely done and i'm a rude bugger not to say so :)
(I helped save b3ta! boris the spider, Sat 10 May 2008, 22:43, archived)
# no i mean it wouldn't be additive even if you undid the logarithms,
i.e. if you put all the stars in the galaxy in one place. I think it probably is meaningless anyway though, like you say. It's just for comparing one galaxy to another.
(I helped save b3ta! Moon Girl Technologies horrendous beanbag, Sat 10 May 2008, 22:46, archived)
# yeah exactly
(luminosity's additive so it would be. if all the stars were in one place so that the whole thing made sense. which they're not. so it doesn't.)

christ i've not thought properly about magnitudes for a very long time. my life hasn't been much emptier.

i'm going to randomly repost a picture to derail this :)

(I helped save b3ta! boris the spider, Sat 10 May 2008, 22:50, archived)