What time is it on the moon?
The Moon Has Its Own Time – How to Track Its Moon With Satellite Navigation, Navigation, and Timing At NASA’s Goddard Flight Center
The moon doesn’t have its own time. Universal time is the standard against which the planets clocks are set and can be done with each lunar mission using its own timescale. The method isn’t very precise and the time isn’t synchronized with each other. The approach works when the Moon hosts a handful of independent missions, but it will be a problem when there are multiple craft working together. Space agencies will also want to track them using satellite navigation, which relies on precise timing signals.
The position, navigation and timing team at NASA’s Goddard Space Flight Center is just starting to lay out a plan, says Cheryl Gramling, who leads the team.
Demonstration of Independent Time on the Lunar Using Satellite Navigation Signals from Earth-based craft and Measurements of Days on the Moon
The alternative would be to use the synthesized output of the lunar atomic clocks as the Moon’s own time and to record its relationship to utc. That way, even if the connection with Earth is lost, clocks on the Moon will still agree with each other and allow safe navigation and communications, says Gramling. An independent time is a model that can work for planets that are not far away, such as Mars. There would be more difficulty in sending tc there than on the Moon.
Representatives of space agencies and academic organizations worldwide met in November 2022 to start drafting recommendations on how to define lunar time at the European Space Research and Technology Centre of the European Space Agency (ESA) in Noordwijk, the Netherlands.
As a first step, from 2024, ESA and NASA will trial deriving positions on the Moon using faint satellite navigation signals from Earth-based craft. The projects plan to place dedicated satellites around the Moon, each with their own atomic clock. The time it takes for a satellite signal to reach the receiver on the Moon is how it triangulates its position. The moon is an important target for exploration because of the amount of water on the lunar south pole, according to an engineer working on a project.
In this scenario, days on the Moon could even be defined differently from those on Earth, to account for the time from solar noon to solar noon taking an average of 29.5 Earth days. The human needs for sleep on a roughly 24 hour cycle make Earth days important to astronauts. Metrologists will need to agree on the definition.
The Moon: What Time Do We Need to Set? A Commentary on Saturn, LunaNet, and Other Space Agency Standardizations of the Circumstellar Environment
Space agencies are also considering other necessary standards — such as which maps of the lunar terrain and coordinate systems to use for navigation — through the Interagency Operations Advisory Group, a council of national space agencies and the United Nations International Committee on GNSS. Gramling says that to make the systems in various countries compatible, reference systems have to be agreed internationally.
With ESA’s help, NASA is developing a framework called LunaNet, for which it hopes to get international buy-in. LunaNet consists of a set of rules that would enable all lunar satellite navigation, communication and computing systems to form a single network similar to the Internet, regardless of which nation installs them. Setting lunar time is part of a much bigger picture.
Everyone agrees on the meaning of a second. (It’s 9,192,631,770 cycles of microwave radiation emitted by a cesium atom, if you’re curious.) But that’s not really helpful when it comes to navigating everyday life. The people who use computers or clock machines need larger chunks of time to be able to get from point A to point B, set a clock or know when to go to work.
Our neighbor rotates at a much slower pace than ours. It means that the side of the moon that is facing away from the sun stays illuminated for a long time. On Earth, we don’t notice this rotation because the moon is locked with us. It takes as long to revolve along its axis as it does to rotate around the planet, so the same side of the moon always faces us.) People like Ventura-Traveset need to know what time means in a place where we no longer use sunrise, sunset or rush hour to guide us.
Whether space agencies adopt a single time zone or several hasn’t been decided yet, Ventura-Traveset says. Given the moon’s slow rotation, he thinks it makes sense to have fewer than Earth’s 24 zones. To him, one zone would be the most practical and natural: We’d reproduce something like Coordinated Universal Time so astronauts could follow a 24-hour cycle as they do on the International Space Station. He doesn’t think it makes sense to have a weeks-long day followed by a weeks-long night, since each day will be out of sync.
