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The year 2009 officially begin a second later after the world's clocks adjust to the increasingly slow rotation of the Earth's axis, today announced the U.S. Naval Observatory.

In this way, when the clocks mark the time 23:59:59 on Wednesday the so-called "universal time", better known as the meridian of Greenwich, was officially added a second.

The observatory, which is responsible for maintaining the "master clock" of the Pentagon, said that the pace of change in the rotation of the earth "occurs at rates affected by changing tides and other factors."

"This is the twenty-fourth extra second is added to the universal time, a uniform scale for measuring the time kept by atomic clocks around the world since 1972," the communique added Observatory.

"Historically the measurement of hourly time was related to half the rotation of the Earth in relation to celestial bodies and the second was defined in this frame of reference," explained the institution.

The invention of atomic clocks defined an "atomic time" much more precise scale and a second that is independent of the rotation of the planet.

In 1970 an international agreement established two scales of measurement of time: one related to the rotation of the Earth and the other in the atomic time.

"The problem is that the rotation of the Earth is becoming more slowly in a very gradual, requiring periodic insertion of a second of extra time scale atomic scales to maintain both a second of each other," said Naval Observatory.