(Image source from: x.com/NASAhistory)
Earth's days are gradually becoming longer, and it is believed that they could eventually reach 25 hours as the planet's rotation slows down. This slowing is caused by the Moon's pull, shifting water and ice, and long-term changes happening inside the Earth, with effects being measured in milliseconds over centuries rather than minutes in a lifetime. The standard 24-hour day is determined by how long it takes for the Sun to return to the same spot in our sky, rather than by a fixed spin speed. Astronomers have discovered that if you measure Earth's rotation against faraway stars (known as a "sidereal day"), it is a bit shorter, and even the solar day varies slightly over time.
Over very long periods, the evidence shows that days are getting longer. These changes are tiny, so they do not interfere with clocks, schools, or calendars, but they can be tracked through careful measurements taken over many years. The main factor slowing down Earth's spin is the gravitational pull of the Moon, which creates tidal bulges in the oceans. Due to friction, these bulges trail behind the Moon slightly, pulling back on the planet's spin and transferring a small amount of rotational energy to the Moon, which slowly moves further away. Changes on the Earth's surface are also important. Studies backed by NASA that use over 120 years of data indicate that melting ice sheets, shrinking glaciers, decreasing groundwater, and rising sea levels slightly shift mass, adjusting the spin axis and adding tiny fractions of a millisecond to the length of the day. Human-caused warming has sped up these processes since around the year 2000, particularly because of rapid ice melting in Greenland and Antarctica.
Today’s geodesy relies on radio signals from distant quasars and lasers aimed at satellites to measure Earth's rotation and movements at the poles with incredible accuracy. Machine learning analyzes data spanning about 120 years and reveals consistent patterns mostly related to water and ice, with a smaller effect from deep Earth activities. Changing a 24-hour day into a 25-hour day is not something that will happen soon but is a gradual process over geological time. The future of this transformation is so far off it is nearly beyond imagination. Current knowledge about the Earth-Moon system indicates it would take approximately 200 million years before a full 25-hour day occurs.
For people today, this notion makes sense scientifically but does not have immediate practical implications, while what’s truly happening now is how gently our planet is already adjusting to tides, ice, and climate changes, millisecond by millisecond.
