Earth Is Spinning Faster, Making Some Summer Days Shorter

It wouldn’t be summer without the stretched out days. The dawns break early and the dusks come late, affording more time for lazy beach trips and long barbecues under the slow curve of the sun.

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 this year’s shortest are happening in July and August.

This week has seen the shortest days of the year so far. According to data from the U.S. Naval Observatory and the International Earth Rotation and Reference Systems Service, Tuesday’s rotation was about 1.34 milliseconds less than 24 hours.

More quick spins are expected this week, later this month and in early August, according to predictions from the website Time and Date.

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 opposite. For many millenniums, the days have been growing longer. A Tyrannosaurus rex that lived 70 million years ago would have experienced an average daily rotation of about 23 1/2 hours, studies have found.