Astronomy Picture of the Day

Explanation: December's 9.0 earthquake has likely shortened Earth's day by about three microseconds and may also have tweaked Earth's rotational wobble. The megathrust earthquake occurred as the Indian tectonic plate slid further beneath the Burma tectonic plate. The earthquake was the fourth most powerful since the year 1900 and triggered tsunamis that tragically killed over 250,000 people in nearby coastal regions. In the above map, the yellow star indicates the location of the main earthquake, while circles show the locations of large aftershocks. The Sumatra-Andaman Islands earthquake's effect on the Earth's rotation was sudden but much smaller than the accumulated effects of other surface events such as an El Nino.