Have you heard the intriguing claim that Earth might one day have 25-hour days? The core idea behind this is scientifically sound. Our planet's spin is indeed gradually slowing down. However, the crucial detail often missed is the incredibly slow pace of this change. These shifts are so gradual they are imperceptible in our daily lives, unfolding over epochs far longer than a human lifespan.
Is a Day Really a Fixed 24 Hours?
We structure our lives around a consistent 24-hour cycle, from school bells to work schedules. But this solar day—the time for the Sun to return to the same point in the sky—is not perfectly constant. Scientists note it stretches and shrinks minutely. If we measure a day against distant stars instead of the Sun, we get a slightly shorter 'sidereal day'. Over vast timescales, the undeniable trend is that solar days are getting longer.
The Moon's Gravitational Brake and Climate Change's Role
The primary driver of Earth's slowing spin is our celestial neighbour, the Moon. Its gravity creates ocean tides. As Earth rotates, friction from these moving tidal bulges against the seabed acts like a gentle brake, sapping a tiny amount of rotational energy. This lost energy transfers to the Moon, pushing it slightly farther away each year.
Beyond this ancient celestial tug-of-war, human activity is now leaving a measurable imprint. NASA-funded research analysing over 120 years of data reveals that the rapid melting of ice sheets in Greenland and Antarctica, along with the movement of groundwater to oceans, is redistributing Earth's mass. This affects the planet's spin axis—a phenomenon called polar motion—and contributes a small but accelerating increase to the day's length. Since around the year 2000, this effect has intensified, linked by scientists to greenhouse gas emissions.
Measuring Millisecond Changes and a Distant Future
How do scientists track these minuscule changes? Modern techniques are extraordinarily precise, using tools like lasers fired at satellites and radio signals from quasars billions of light-years away. Machine learning analyses have helped separate the causes, identifying patterns tied to surface changes like ice loss and deeper Earth processes.
So, when will we actually need to adjust our clocks for a 25-hour day? The timeline is almost beyond human comprehension. Based on the current understanding of the Earth-Moon system, reaching a 25-hour day would take roughly 200 million years. For now, the change is a matter of milliseconds accumulated over centuries—a silent, slow-motion transformation of our planet.
