Here's a question that just happened to pop into my mind at such an awful early hour in the morning...
So the Green Lantern Corps; guardians of galactic peace, stability, yada-yada, i.e. the Outer Space PD. The guys with goofy green outfits who can conjure constructs made of pure emerald willpower. They who boldly go where lots of civilizations have frequently gone before. The protectors of the universe for the last three billion years. You get the idea. Why did they let Krypton blow up?
I don't know if this has ever been addressed in pre-Flashpoint continuity or even in the New 52. Has Superman ever taken a look at his ring slinging clover colored buddy Hal and asked "Hey Hal, what the crap man?! You guys just sat on your big green (removed for the sake of the children) and just let my entire civilization turn into space dust!"
Was it because Krypton just had an immediate stomach ache and the core just decided to get more elbow room by taking off it's coat? I always thought that Jor-El had known for some time and was trying to get everyone genuinely concerned about Krypton having an internal meltdown - hence why he had time to build a rocket for his son. So you'd think in that time; word might get out to the local Green Lantern (whoever that was) that "Dude, Krypton's going to go out with a Earth shattering ka-boom in like two days." Even then, I'd assume that an organization as illustrious and respected as the Green Lantern Corps would be known about by the people of Krypton and therefore Jor-El so why didn't he ask them for help?
Were they busy? Was it a holiday? Did the Guardians sit down and agree to a unanimous "Meh." about the fate on an entire race? Were there diplomatic breakdowns between Krypton and Oa; were people smuggling Kryptonain cigars into Thanagar?
So I put it towards the good people of ComicVine to help me answer this. I will not accept any answer that consists with the logic of "It was pre-determined in the Book of Oa." if that is indeed how the book works.