Earth heading for 25-hour day as orbit slows

Days on Earth are getting longer, a team of experts has concluded, as they predict in the future there will be 25 hours in a day.

Over the past 27 centuries, the average day has lengthened at a rate of almost two milliseconds (ms) per century.

However, it will take about 6.7 million years to gain just one minute extra per day and we will have to wait about 200 million years for the extra hour.

Study lead co-author Leslie Morrison said: "It's a very slow process."

Researchers at Durham University and the UK's Nautical Almanac Office gathered evidence from historical accounts of eclipses and celestial events from 720BC to 2015.

Mr Morrison, a retired astronomer with Royal Greenwich Observatory, said the earth's orbit is not slowing as rapidly as first expected.

It was previously estimated it will take 5.2 million years to add one minute to every day.

"These estimates are approximate, because the geophysical forces operating on the Earth's rotation will not necessarily be constant over such a long period of time," Mr Morrison said.

The team of experts used gravitational theories about the movement of Earth around the Sun, and the Moon around Earth, to compute the timing of eclipses of the Moon and Sun over time, as viewed from our planet.

They then calculated from where on Earth these would have been visible, and compared this to observations of eclipses recorded by ancient Babylonians, Chinese, Greeks, Arabs and medieval Europeans.

Mr Morrison said: "For example, the Babylonian tablets, which are written in cuneiform script, are stored at the British Museum and have been decoded by experts there and elsewhere."

The team found discrepancies between where the eclipses should have been observable, and where on Earth they were actually seen.

The Earth's rotation can be influenced by factors including its altering shape due to shrinking polar ice caps since the last Ice Age, electro-magnetic interactions between the mantle and core, and changes in the sea level.