Far more people watched Thursday's vice presidential debate between Joe Biden and Sarah Palin on television than watched the first presidential debate.

Nielsen Media Research says preliminary ratings in the nation's 55 biggest markets were up 42 percent from the same measurement of John McCain and Barack Obama's first encounter last Friday.

Nielsen's specific estimate of how many people watched Thursday night will be out later, but indications are it will be one of the most-watched political debates ever.

Curiosity over Palin's performance undoubtedly played a role, but don't discount timing: More people generally watch television on Thursdays than Fridays.