Yesterday was just a tiny bit shorter because of the giant earthquake off the coast of Japan.
Nasa geophysicist Richard Gross calculated that Earth's rotation sped up by 1.6 microseconds.
That is because of the shift in Earth's mass caused by the 8.9-magnitude earthquake. A microsecond is one-millionth of a second.
That change in rotation speed is slightly more than the one caused by last year's larger Chile earthquake.
But 2004's bigger Sumatra earthquake caused a 6.8-microsecond shortening of the day.
The Japan quake was the fifth strongest since 1900.