A clock on the Moon? Here’s how time will be measured in space
At the ‘International Conference on Weights and Measures’ in Versailles, work is under way to establish an international method for measuring time using Earth-orbiting satellites
To establish a common standard for measuring time on the Moon. This is the task set by the International Conference on Weights and Measures, which will conclude tomorrow, 15 October, in Versailles, France. This need has been highlighted by the space agencies of several countries in order to ensure a consistent approach during international missions.
Why terrestrial clocks aren’t suitable
A natural question springs to mind: ‘Why can’t we stick to Earth time?’ Because gravity changes. According to the theory of relativity, gravity and speed affect the rate at which clocks tick. On the Moon, gravity is about one-sixth that of Earth’s, and so there are differences in the measurement of time. Whilst the discrepancy has imperceptible effects on a day-to-day basis, in the context of space operations, even microseconds of difference can result in a significant margin of error.
How to measure time on the Moon
There are two key steps to be taken in order to arrive at a shared standard: deciding which reference to adopt and how to link it to atomic clocks. Atomic clocks are the most accurate instruments ever built for measuring time, with an uncertainty of one second every 300 million years. It is the ability to synchronise clocks in a stable and comparable manner that underpins the functioning of a time system.
In practical terms, the experts must draw up common rules regarding how to count seconds, how to correct for differences caused by gravity, and how to exchange signals between the lunar surface, orbiting probes and ground control centres.
Building a lunar clock will enable international working groups to collaborate using standardised tools, improve telecommunications and make satellite positioning more efficient.
