How do turtles navigate in the ocean?

Did you know that sea turtles always lay their eggs on the exact same beach they have been hatched? But they also have these amazing journeys across the vast oceans. How could they know where their beach is? And how do they even find their way there? 

Actually, scientists have known those answers for years. Turtles use to sense the earth's magnetic field, the same thing that makes your compass always point north. But that's not all, they can also sense its fluctuations, caused by the surrounding landmass so precisely, they can memorize and recognize it the next time.