A Google-a-Day Puzzle for Dec. 21

Our good friends at Google run a daily puzzle challenge and asked us to help get them out to the geeky masses. Each day’s puzzle will task your googling skills a little more, leading you to Google mastery. Each morning at 12:01 a.m. Eastern time you’ll see a new puzzle, and the previous day’s answer (in invisitext) posted here.

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SPOILER WARNING:
We leave the comments on so people can work together to find the answer. As such, if you want to figure it out all by yourself, DON’T READ THE COMMENTS!

Also, with the knowledge that because others may publish their answers before you do, if you want to be able to search for information without accidentally seeing the answer somewhere, you can use the Google-a-Day site’s search tool, which will automatically filter out published answers, to give you a spoiler-free experience.

And now, without further ado, we give you…

TODAY’S PUZZLE:

Which is longer, the largest cruise ship now in service or the largest aircraft carrier now in service?

YESTERDAY’S ANSWER (mouseover to see):

Search [evolutionary rule polar bear ears] and learn about Allen’s Rule, which says that in order to preserve warmth, animals in colder climates will have shorter appendages (legs, arms, tails … and ears) than a similar animal in a warmer climate.