I once read on starwars.com before it was taken down, that Emperor Palpatine sensed the destruction of the Death Star as a ripple in the Force. He also knew that Luke (Anakin's son) was the one who did it. Is that true?
There were over 1 million people on the Death Star when it blew up. When that many people are killed at one time it can definitely be felt as a ripple in the Force especially to someone as sensitive as Darth Sidious. He probably also felt the rage of his Apprentice as he watched helplessly from space as rebels destroyed the Empire's greatest weapon. He would not have "known" it was the Death Star but knowing the battle is happening I am certain he would have made that conclusion.
I never read or seen anything that would make me believe that Sidious would have known who it was that destroyed the Death Star immediately. However, Luke became very famous throughout the Empire following the Battle of Yavin. I suspect it did not take long for the Empire's intelligence agents to learn the name of the rebel pilot responsible.
I'd say: Not necessarily. First of all, I don't know whether there's been some established "maximum distance" where you could feel such a ripple in a reasonable way. Would it be unlimited, there could be quite some "noise" due to planets getting destroyed by meteor impacts, ships blowing up, etc.
But even ignoring this fact, there's still the question, whether he'd be able to differentiate between the Death Star blowing up or its target blowing up (especially while anticipating the latter). After all there were probably more sentient life forms on the surface than just a few rebels.