A "leap" second, is being added to account for the fact that it is taking Earth longer and longer to complete one full turn. Scientists know this from VLBI measurements, which are also used in the time standard UT1.
VLBI was originally invented in the 1960s to take better pictures of quasars, but scientists soon found that if you threw the process in reverse, you could measure how the ground beneath the telescopes moves around, how long days really are, and how the Earth wobbles on its axis!
The laser altimeter on NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft has returned data that indicate ice may make up as much as 22 percent of the surface material in Shackleton crater at the moon's south pole.
NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft will get a "front-row seat" to the total lunar eclipse on Dec. 10, 2011, and will take temperature measurements as Earth's shadow blankets the moon.
Noah Petro explains how the new images of three Apollo landing sites give us a clearer view of where the astronauts went, where they sampled and where they conducted scientific experiments on the lunar surface.