The devastating earthquake which struck Chile on February 27th may well have had an effect on the rotation of the Earth itself according to a NASA scientist. Richard Gross of the Jet Propulsion Laboratory has used computer models to calculate that our day is now about 1.26 microseconds shorter than it was on February 26th.
A small amount and yet it serves as a reminder that whilst we have exactly twenty four hours in our standard day, this never quite matches the actual rotation period of the Earth. Back in 1999 Gross published a paper in Physics of the Earth and Planetary Interiors in which he modeled the spin of the Earth from 1832 to 1997. The shortest day on record was apparently August 2nd 2004 whereas the longest day was sometime during 1912, the year the Titanic sank.
“The annual changes in the length of the day are caused mostly by the atmosphere – changes in the strength and direction of the winds, especially the jet stream. The Sun warms the equator more than the poles. That temperature difference is largely responsible for the jet stream. Seasonal changes in that temperature difference cause changes in the winds and, hence, the length of the day,” says Gross.
More significant events, like those in Chile, can enhance this process. The quake, which measured 8.8 on the magnitude scale, is also likely to have knocked the Earth’s axis slightly out of its previous alignment by about 2.7 milliarcseconds (roughly 3 one thousandths of one 3600th of a degree) or the equivalent of about seven centimetres.
Whilst this might not sound significant, knowing the precise alignment of the Earth is crucial for many modern day technologies such as GPS. And in an age where solar system exploration is on the increase, knowing the precise location of the Earth’s orientation with respect to these craft is a fundamental part of planning successful interplanetary maneuvers.