If you think that every day of your life has exactly 24 hours, you are sorely mistaken. As scientists know, the length of the day changes periodically due to changes in the Earth's rotation. Now a study "measures" for the first time exactly when this happens, and even identifies an "extra", previously unknown factor that "plays" with our twenty-four hours and seems to be linked to the Earth's magnetic field.
"Hiccup" in the Earth's rotation
The Earth's rotation fluctuates every year or decade due to changes in its atmosphere and oceans, as well as in its interior, its mantle and core. However, the exact changes that these fluctuations cause during the day and the "patterns" that they follow were not fully known to scientists. A team of researchers led by Richard Holm of the University of Liverpool in Britain analyzed astronomical and satellite data from 1969 to the present in order to record them.
In their study, published in the journal Nature, they present the clearest picture of the length of our twenty-four hours in fifty years. The researchers identified three different factors that cause “hiccups” in the Earth’s motion as it rotates – and that vary the length of our day in three different cycles.
Influences from the "insides" of the planet
First, they documented in detail a well-known variation, in which the length of the day increases or decreases by a few milliseconds every decade or so, before returning to its "normal" levels. This variation is due to slow changes occurring in the Earth's core.
The second cycle recorded is also due to processes occurring inside the planet, specifically the continuous oscillations observed from the interaction of its liquid core and solid mantle, and until now was not well known to experts. As it turned out, this cycle lasts 5.9 years and changes the length of the day by fractions of a millisecond every year.
Magnetic bounce
But the researchers also recorded a third category of changes that had not been observed before. They saw that three times in recent years, namely in 2003, 2004 and 2007, the planet's rotation experienced small "bounces." These bounces intersperse the longer-term changes by a fraction of a millisecond and last for a few months before things return to normal.
By examining satellite data on Earth's magnetic field over the past 20 years, scientists have seen similar jumps in the planet's magnetic field, coinciding with the rotation. Mr. Holm suspects that these sudden changes may be caused when a piece of molten core temporarily attaches to the mantle, changing the Earth's angular velocity.
