Yes, technically I am a liberal arts major, but I did study science along with writing, and xkcd makes me giggle often enough that I have the site bookmarked.
This recent strip on the Stingray Nebula, for example, is both profound and hilarious. BUT, I have a quibble.
Click the picture below to read the full comic, then check out the rest of this post to see if you have the same quibble…
And now, the quibble: In the next-to-last frame, if the Stingray Nebula he means is Hen-1357, there was no explosion.
This Stingray is what’s called a planetary nebula, all that’s left of a low- to medium-mass star that puffed up to become a red giant and then expelled its outer layers of gas.
—Image courtesy Matt Bobrowsky, Orbital Sciences Corporation and NASA/ESA
He is right that an asymptotic giant branch, or AGB, star formed the Stingray—because AGBs represent a late stage in stellar evolution, when a red giant is very close to becoming a nebula.
A main sequence star is simply the term for a star that’s still fusing hydrogen into helium in its core, and so is relatively stable. A red, yellow, or orange dwarf star would be on the low-mass end of the main sequence.
Really, main sequence stars (and dwarfs) can’t be trusted either, because they will eventually evolve into red giants too or—if they are more than ten times the sun’s mass—their cores will collapse, triggering supernovae or forming black holes.
I guess the difference is that you’re not likely to see a main sequence star change much during a human lifetime, while the Stingray Nebula was initially classified as a star and was later found to be the youngest known planetary nebula, which has dropped in brightness since the 1980s.
Anyway, enough geeking out. The comic is still awesome, and the best part is the alt tag… true that.