Timekeeping on the Moon#Coordinated Lunar Time
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{{redirects|Moon time|Earth calendars using the Moon|lunar calendar}}
Timekeeping on the Moon is an issue of synchronized human activity on the Moon 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 or lunar month, observable from Earth as the lunar phases, and the rate at which time progresses, with 24 hours on the Moon being 58.7 microseconds (0.0000587 seconds) faster,{{cite web
| access-date = 2024-04-06
| date = 2024-04-03
| first = Diana
| last = Ramirez-Simon
| title = Moon Standard Time? Nasa to create lunar-centric time reference system
| url = https://theguardian.com/science/2024/apr/02/moon-nasa-coordinated-lunar-time
| website = the Guardian
}} resulting from gravitational time dilation due to the different masses of the Moon and Earth.
History
{{see also|History of timekeeping devices}}
file:Buzz Aldrin in the Lunar Module during Apollo 11 LM checkout (48322616012).jpg wearing an Omega Speedmaster watch during 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).{{cite magazine
| magazine = Air & Space Magazine {{!}} Smithsonian Magazine
| title = The Watches That Went to the Moon
| url = https://smithsonianmag.com/air-space-magazine/space-timekeepers-180957295
}}
The Apollo Guidance Computer (AGC) kept a triple-precision count of time in a real time clock cuing from a quartz oscillator; 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, 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.{{cn|date=April 2024}}
Coordinated Lunar Time
Coordinated Lunar Time (LTC) is a proposed primary lunar time standard for the Moon.{{cite web
| access-date = April 3, 2024
| archive-date = April 3, 2024
| archive-url = https://web.archive.org/web/20240403162237/http://esa.int/Applications/Satellite_navigation/Telling_time_on_the_Moon
| date = February 27, 2023
| title = Telling time on the Moon
| url = https://esa.int/Applications/Satellite_navigation/Telling_time_on_the_Moon
| url-status = live
| work = European Space Agency
}} In early April 2024, the White House asked NASA 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.{{cite news
| access-date = 2024-04-03
| archive-date = 2024-04-02
| archive-url = https://web.archive.org/web/20240402195402/http://reuters.com/science/white-house-directs-nasa-create-time-standard-moon-2024-04-02
| date = 2024-04-03
| first1 = Joey
| first2 = Will
| last1 = Roulette
| last2 = Dunham
| publisher = Reuters
| title = Exclusive: White House directs NASA to create time standard for the moon
| url = https://reuters.com/science/white-house-directs-nasa-create-time-standard-moon-2024-04-02
| url-status = live
}} The White House's request, led by the Office of Science and Technology Policy (OSTP), called for a "Coordinated Lunar Time", which was first proposed by the European Space Agency in early 2023.{{cite web
| access-date = October 26, 2024
| archive-date = March 1, 2023
| archive-url = https://web.archive.org/web/20230301040012/http://nbcphiladelphia.com/news/national-international/should-the-moon-have-a-time-zone-europe-pushes-for-lunar-reference-time/3510971
| date = March 1, 2023
| title = Should the Moon Have a Time Zone? Europe Pushes for 'Lunar Reference Time'
| url = https://nbcphiladelphia.com/news/national-international/should-the-moon-have-a-time-zone-europe-pushes-for-lunar-reference-time/3510971
| url-status = live
| website = NBC Philadelphia
}}
{{as of|2024|10}}, there is no lunar time standard. As a result, activities on the Moon are coordinated using the time zone of where a mission's headquarters is based.{{cite web
| access-date = April 3, 2024
| archive-date = April 3, 2024
| archive-url = https://web.archive.org/web/20240403175022/http://space.com/moon-time-lunar-clock-debate-wristwatch
| author-link = Joe Rao
| date = May 9, 2023
| first = Joe
| last = Rao
| title = What time is it on the moon? How a lunar clock debate led to an out-of-this-world timepiece
| url = https://space.com/moon-time-lunar-clock-debate-wristwatch
| url-status = live
| website = Space.com
}} For example, the Apollo missions utilized the Central Time Zone as the missions were controlled from Houston, Texas.{{cite journal
| access-date = 2024-04-03
| archive-date = 2023-04-03
| archive-url = https://web.archive.org/web/20230403113210/http://nature.com/articles/d41586-023-00185-z
| bibcode = 2023Natur.614...13G
| doi = 10.1038/d41586-023-00185-z
| first1 = Elizabeth
| issue = 7946
| journal = Nature
| last1 = Gibney
| pages = 13–14
| pmid = 36693973
| s2cid = 256230630
| title = What time is it on the Moon?
| url = https://nature.com/articles/d41586-023-00185-z
| url-status = live
| volume = 614
| year = 2023
| url-access= subscription
}} Likewise, Chinese activities on the Moon run on China Standard Time.{{citation needed|date=October 2024}} 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, especially in the United States and China,{{cite web
| access-date = April 4, 2024
| date = January 12, 2024
| first1 = Joey
| first2 = Nivedita
| first3 = Ryan
| last1 = Roulette
| last2 = Bhattacharjee
| last3 = Woo
| title = In moon race with China, U.S. setbacks test role of private firms
| url = https://reuters.com/science/moon-race-with-china-us-setbacks-test-role-private-firms-2024-01-12
| website = Reuters
| access-date = April 4, 2024
| archive-date = January 12, 2024
| archive-url = https://web.archive.org/web/20240112012346/http://space.com/return-to-moon-china-space-race
| date = July 20, 2023
| first = Rick
| last = Tumlison
| title = Return to the moon: The race we have to win (again)
| url = https://space.com/return-to-moon-china-space-race
| url-status = live
| website = Space.com
}} a need exists for a universal time-keeping benchmark so that lunar spacecraft and satellites are able to fulfill their respective missions with precision and accuracy.{{cite web
| access-date = April 9, 2024
| date = April 7, 2024
| first = Sharmila
| last = Kuthunur
| title = White House directs NASA to create a new time zone for the moon
| url = https://space.com/white-house-nasa-time-zone-moon
| website = Space.com
| access-date = April 4, 2024
| archive-date = January 24, 2024
| archive-url = https://web.archive.org/web/20240124133333/http://space.com/does-moon-need-its-own-time-zone
| date = March 1, 2023
| first = Robert
| last = Lea
| title = Does the moon need its own time zone? We may need to decide soon
| url = https://space.com/does-moon-need-its-own-time-zone
| url-status = live
| website = Space.com
}} Due to differences in gravitational force and other factors, time passes fractionally faster on the Moon when observed from Earth.{{cite news
| access-date = 2024-04-03
| archive-date = 2024-04-03
| archive-url = https://web.archive.org/web/20240403014614/http://theguardian.com/science/2024/apr/02/moon-nasa-coordinated-lunar-time
| date = 2024-04-03
| first = Diana
| issn = 0261-3077
| language = en-GB
| last = Ramirez-Simon
| title = Moon Standard Time? Nasa to create lunar-centric time reference system
| url = https://theguardian.com/science/2024/apr/02/moon-nasa-coordinated-lunar-time
| url-status = live
| work = The Guardian
| access-date = 2024-04-24
| language = en-US
| date = 2024-04-22
| first = Sharmila
| last = Kuthunur
| title = What time is it on the Moon? We might soon know
| url = https://astronomy.com/observing/what-time-is-on-the-moon-we-might-soon-know
| website = Astronomy Magazine
}}
Under the Artemis program, and supported by the Commercial Lunar Payload Services missions, astronauts and a proposed scientific moonbase are envisioned to take place on and around the lunar surface from the 2020s onwards.{{cite web
| access-date = 2024-04-03
| archive-date = 2024-04-03
| archive-url = https://web.archive.org/web/20240403000216/http://esa.int/Applications/Navigation/Telling_time_on_the_Moon
| language = en
| title = Telling time on the Moon
| url = https://esa.int/Applications/Navigation/Telling_time_on_the_Moon
| url-status = live
| website = esa.int
}} The proposed standard would therefore solve a timekeeping issue.{{cite web
| access-date = April 4, 2024
| archive-date = April 4, 2024
| archive-url = https://web.archive.org/web/20240404225558/http://smithsonianmag.com/smart-news/the-moon-will-get-its-own-time-zone-called-coordinated-lunar-time-under-nasas-lead-180984076
| date = April 4, 2024
| first = Christian
| last = Thorsberg
| newspaper = Smithsonian
| title = NASA Will Create a New Time Zone for the Moon, Called Coordinated Lunar Time
| url = https://smithsonianmag.com/smart-news/the-moon-will-get-its-own-time-zone-called-coordinated-lunar-time-under-nasas-lead-180984076
| url-status = live
}} According to OSTP Chief Arati Prabhakar, 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".{{cite web
| access-date = April 4, 2024
| archive-date = April 3, 2024
| archive-url = https://web.archive.org/web/20240403220123/http://thehill.com/homenews/4573225-nasa-tasked-creating-time-zone-moon
| date = April 3, 2024
| first = Lauren
| last = Irwin
| newspaper = The Hill
| title = NASA tasked with creating a time zone for the moon
| url = https://thehill.com/homenews/4573225-nasa-tasked-creating-time-zone-moon
| url-status = live
}}
The development of the standard is set to be a collaborative effort, initially amongst members of the Artemis Accords, but will be meant to apply globally. The initial proposal of the standard calls for four key features:{{cite web
| access-date = April 4, 2024
| archive-date = April 4, 2024
| archive-url = https://web.archive.org/web/20240404144456/http://whitehouse.gov/wp-content/uploads/2024/04/Celestial-Time-Standardization-Policy.pdf
| author = Prabhakar, Arati
| date = April 2, 2024
| title = Policy on Celestial Time Standardization in Support of the National Cislunar Science and Technology (S&T) Strategy
| url = https://whitehouse.gov/wp-content/uploads/2024/04/Celestial-Time-Standardization-Policy.pdf
| url-status = dead
| website = The White House
}}
- traceability back to Coordinated Universal Time,
- 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 European Space Agency, calls for a Lunar Time System Standard which the LTC is meant to address.{{cite web
| access-date = 2024-04-03
| archive-date = 2024-04-05
| archive-url = https://web.archive.org/web/20240405115535/http://spacenews.com/white-house-directs-nasa-to-develop-lunar-time-standard
| date = 2024-04-03
| first = Jeff
| language = en-US
| last = Foust
| title = White House directs NASA to develop lunar time standard
| url = https://spacenews.com/white-house-directs-nasa-to-develop-lunar-time-standard
| url-status = live
| website = SpaceNews
}}
In August 2024, the US National Institute of Standards and Technology 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.{{cite journal
| date = 2024-08-12
| journal = NIST
| language = en
| title = What Time Is It on the Moon?
| url = https://nist.gov/news-events/news/2024/08/what-time-it-moon
}}
See also
- {{annotated link|International Celestial Reference System and its realizations}}
- {{annotated link|Lunar calendar}}
- {{annotated link|Month}}
- {{annotated link|Nautical time}}
- {{annotated link|Sidereal time}}
- {{annotated link|Timekeeping on Mars}}