What time is it on the moon? – New Scientist

Future lunar missions and plans for a permanent lunar base call for accurate clocks. But because atomic clocks tick differently on the moon than on Earth, the question arises: what time is it on the moon?

Dozens of lunar missions are planned for the next ten years. The American space agency NASA wants to put people on the moon again in a few years with the Artemis mission. And there are even plans for a permanent lunar base.

So it’s time to think about how we determine times on the moon. If no official lunar time is set, space agencies and private companies will come up with their own solutions, says Patricia Tavella in an article Nature. She is in charge of the time department at the International Bureau of Weights and Measures in France. “We want to issue a warning now and say, let’s work together to make a common decision.”

Need a moon time

There is currently no agreed upon ‘moon time’. Each lunar mission operates with its own clock, which is linked to Coordinated Universal Time (UTC) via a control center on Earth. That works fine if there are only a few independent lunar missions. But if you want lunar explorers to work together, then a defined, coordinated time is needed.

An official lunar time is also important because space agencies NASA and ESA satellite navigation (similar to the GPS system) and telecommunications on the moon. There are even plans to connect all computer systems on the moon via a lunar internet, called LunaNet.

Tap issues

But it is not easy to determine a lunar time. Clocks on the moon tick faster than those on Earth. Einstein’s general theory of relativity states that clocks tick faster in weak gravitational fields – such as those of the moon.

If you turned on two super-accurate clocks on the moon and on Earth at exactly the same time, the one on the moon would be ahead by about 56 microseconds after 24 hours.

Dependent or independent

The way to define a lunar time starts with installing three atomic clocks on the moon. They will tap on the ‘moon rhythm’. Those three clocks will be combined with a computer program to prevent small, individual deviations from throwing a spanner in the works. Together, these clocks form an accurate, virtual moon clock.

Determining a lunar time using this moon clock can be done in different ways. You could use world time UTC for that. This is useful if there is a lot of communication with the earth. But that does mean that you have to constantly synchronize the lunar clock with world time on Earth to keep the two in sync.

Another option is to keep to the time of the virtual moon clock. The moon then has its own time, independent of the Earth’s time. In that case, you should pay close attention to the difference between lunar time and coordinated world time when communicating between the two locations. The advantage is that mutual communication and navigation on the moon continue to run smoothly if the central lunar clock (temporarily) loses contact with the earth.

Decision time

Various space organizations and metrologists are discussing how they will determine lunar time. It must also be decided where the three atomic clocks will be placed. That could be somewhere on the lunar surface, or in orbit around the moon.

In any case, in order to steer the expected stream of moon missions in the right direction, it is high time that we started working on the question: what time is it on the moon?