SCIENCE LAB SCOPES : SPIN CYCLES

'' FOR now at least - those long summer days are really the opposite '' : It wouldn't be summer without the stretched-out days. The dawns break early and the dusk comes late.

But when it comes to the full astronomical day - a single rotation of planet Earth in which the hour hand moves twice around a standard clock - some of the year's shortest are happening in July and August.

Last week saw the shortest days of the year so far. According to data posted on Friday from the U.S. Naval Observatory and the International Earth Rotation and Reference Systems Service, Wednesday's rotation was about 1.34 milliseconds less than 24 hours. More quick spins are expected in August.

This isn't completely out of the ordinary : Our world's spins have been faster than usual lately.

The average day has mostly shortened over the past decade, and within the past five years or so, the full rotation has clocked in at a hair less than 24 hours more often than not.

Factors driving the change include movements at Earth's core, atmospheric changes and the moon's position.

But long-term trends do not suggest that the days will shorten in perpetuity. In fact, it is just the reverse. For many millenniums, the days have been growing longer. A dinosaur that lived 70 million years ago would have experienced an average daily rotation of about 23 and half hours.

The lengthening trend is expected to continue, said Clark R. Wilson, a research professor at the Center for Space Research at the University of Texas, though the process is so slow as to be '' well beyond human time scales.''

The main reason has to do with energy lost from the tides. The moon's gravitational tug is responsible for tidal changes on Earth. Tidal currents heat the ocean slightly, dissipating energy, which slows the Earth's rotation and lets the moon move further away as time passes.

The World Students Society thanks Jacey Fortin.