Timekeeping on the Moon is an issue of synchronized human activity on the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

and contact with such. The two main differences to timekeeping on Earth are the length of a day on the Moon, being the

lunar day A lunar day is the time it takes for Earth's Moon to complete on its axis one synodic rotation, meaning with respect to the Sun. Informally, a lunar day and a lunar night is each approximately 14 Earth days. The formal lunar day is therefore t ...

lunar month In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. Variations In Shona, Middle Eastern, and Euro ...

, observable from Earth as the

lunar phases A lunar phase or Moon phase is the apparent shape of the Moon's directly sunlit portion as viewed from the Earth. Because the Moon is Tidal locking, tidally locked with the Earth, the same Hemisphere (geometry), hemisphere is always facing the ...

, and the rate at which time progresses, with 24 hours on the Moon being 58.7

microseconds A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, ...

(0.0000587 seconds) faster, resulting from

gravitational time dilation Gravitational time dilation is a form of time dilation, an actual difference of elapsed time between two events, as measured by observers situated at varying distances from a gravitating mass. The lower the gravitational potential (the closer ...

due to the different masses of the Moon and Earth.

History

Buzz Aldrin wearing an Omega Speedmaster watch during Apollo 11">Omega_Speedmaster.html" ;"title="Buzz Aldrin wearing an Omega Speedmaster">Buzz Aldrin wearing an Omega Speedmaster watch during alt=an astronaut with short hair and wearing a watch, flight suit and commset looks at the camera The technology used for the timekeeping device">Apollo 11 mission in 1969">alt=an astronaut with short hair and wearing a watch, flight suit and commset looks at the camera The technology used for the timekeeping devices deployed to the Moon have varied over the decades. Several Omega Speedmasters have been on the Moon, synched to Central Standard Time (CST). The Apollo Guidance Computer (AGC) kept a triple-precision count of time in a real time clock cuing from a

quartz oscillator A crystal oscillator is an electronic oscillator circuit that uses a piezoelectric crystal as a frequency-selective element. The oscillator frequency is often used to keep track of time, as in quartz wristwatches, to provide a stable clock ...

; a standby option (although never used) would allow it to update this count every 1.28 second (~0.78 hertz) — more often when not standing by. In addition to maintaining the

clock cycle In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') is an electronic logic signal (voltage or current) which oscillates between a high and a low state at a constant frequency and ...

, computer timekeeping allowed the AGC to display the capsule's vertical and horizontal movements relative to the Moon's surface, in units of

feet per second The foot per second (plural feet per second) is a unit of both speed (scalar) and velocity (vector quantity, which includes direction). It expresses the distance in feet (ft) traveled or displaced, divided by the time in seconds (s). The corre ...

Coordinated Lunar Time

Coordinated Lunar Time (LTC) is a proposed primary lunar time standard for the

. In early April 2024, the

White House The White House is the official residence and workplace of the president of the United States. Located at 1600 Pennsylvania Avenue Northwest (Washington, D.C.), NW in Washington, D.C., it has served as the residence of every U.S. president ...

asked

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

to work alongside US and international agencies for the purpose of establishing a unified standard time for the Moon and other celestial bodies by 2026. The White House's request, led by the

Office of Science and Technology Policy The Office of Science and Technology Policy (OSTP) is a department of the United States government, part of the Executive Office of the President of the United States, Executive Office of the President (EOP), established by United States Congres ...

(OSTP), called for a "Coordinated Lunar Time", which was first proposed by the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

in early 2023. , there is no lunar

time standard A time standard is a specification for measuring time: either the rate at which time passes or points in time or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of cu ...

. As a result, activities on the Moon are coordinated using the time zone of where a mission's headquarters is based. For example, the

Apollo missions The Apollo program was a United States human spaceflight program carried out from 1961 to 1972 by the National Aeronautics and Space Administration (NASA), which landed the first astronauts on the Moon. The program used the Saturn IB and Saturn V ...

utilized the

Central Time Zone The North American Central Time Zone (CT) is a time zone in parts of Canada, the United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It ...

as the missions were controlled from Houston, Texas. Likewise, Chinese activities on the Moon run on

China Standard Time The time in China follows a single standard UTC offset, time offset of UTC+08:00, where Beijing is located, even though the country spans five geographical time zones. It is the largest sovereign nation in the world that officially observes only ...

. As more countries are active on the Moon and interact with each other, a different, unified system will be needed. With renewed international interest in human travel to the moon, reminiscent of the

space race The Space Race (, ) was a 20th-century competition between the Cold War rivals, the United States and the Soviet Union, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between t ...

, especially in the United States and China, a need exists for a universal time-keeping benchmark so that lunar

spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...

and

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

s are able to fulfill their respective missions with precision and accuracy. Due to differences in

gravitational force Newton's law of universal gravitation describes gravity as a force by stating that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the sq ...

and other factors, time passes fractionally faster on the Moon when observed from Earth. Under the

Artemis program The Artemis program is a Exploration of the Moon, Moon exploration program led by the United States' National Aeronautics and Space Administration (NASA), formally established in 2017 via Space Policy Directive 1. The program's stated long-ter ...

, and supported by the

Commercial Lunar Payload Services Commercial Lunar Payload Services (CLPS) is a NASA program to hire companies to send small robotic landers and rovers to the Moon. Most landing sites are near the lunar south pole where they will scout for lunar resources, test in situ resource ...

missions, astronauts and a proposed scientific

moonbase A moonbase (or lunar base) is a human outpost on or below the surface of the Moon. More than a mere site of activity or temporary camp, moonbases are extraterrestrial bases, supporting uncrewed spaceflight, robotic or crewed spaceflight, human a ...

are envisioned to take place on and around the lunar surface from the 2020s onwards. The proposed standard would therefore solve a timekeeping issue. According to OSTP Chief

Arati Prabhakar Arati Prabhakar (born February 2, 1959) is an American engineer and public official. From October 3, 2022 to January 20, 2025, she served as the 12th director of the White House Office of Science and Technology Policy and the Science Advisor to ...

, time would "appear to lose on average 58.7 microseconds per Earth-day and come with other periodic variations that would further drift Moon time from Earth time". The development of the standard is set to be a collaborative effort, initially amongst members of the

Artemis Accords The Artemis Accords are a series of non-binding multilateral arrangements between the United States government and other world governments that elaborates on the norms expected to be followed in outer space. The Accords are related to the Artem ...

, but will be meant to apply globally. The initial proposal of the standard calls for four key features: * traceability back to

Coordinated Universal Time Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communicat ...

, * accuracy sufficient for navigation and science, * resilience to disruptions, and * scalability to potential environments beyond cislunar space. LunaNet, an upcoming lunar communications and navigation service under development with the

, calls for a Lunar Time System Standard which the LTC is meant to address. In August 2024, the US

National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into Outline of p ...

furthered development of the proposal by releasing a draft for the standard focused on defining the framework and mathematical model. The draft takes into account the gravitational differences on the Moon and was published to ''

The Astronomical Journal ''The Astronomical Journal'' (often abbreviated ''AJ'' in scientific papers and references) is a peer-reviewed monthly scientific journal owned by the American Astronomical Society (AAS) and currently published by IOP Publishing. It is one of the p ...

''.

References

{{reflist category:timekeeping category:moon

History

Coordinated Lunar Time

See also

References