【By Observer.com, Chen Sijia】 In recent years, as lunar exploration has attracted the attention of countries around the world, how to define lunar standard time has become a new issue of concern in the scientific community. According to an article by Hong Kong's South China Morning Post on January 12, the Purple Mountain Astronomical Observatory of the Chinese Academy of Sciences officially released the world's first "Lunar Time Software" last month, achieving accurate conversion between lunar and Earth time.

According to general relativity, due to the moon's gravity being only about one-sixth of Earth's, time on the moon runs faster than on Earth, by about 56 microseconds per day. These small errors accumulate, which can have serious impacts on space missions requiring precise timing.

To solve the problem of time conversion between the moon and Earth, researchers at the Purple Mountain Astronomical Observatory built a model that takes into account the moon's weak gravity and its motion in space, allowing events on the moon to be accurately synchronized with clocks on Earth. Last month, the Purple Mountain Astronomical Observatory officially released the lunar time ephemeris product LTE440.

Photo of the moon taken by astronaut Matthew Domineck on the International Space Station

According to the Chinese Academy of Sciences, one of the key steps in defining and constructing lunar standard time is to clarify the relationship between lunar coordinate time and solar system barycentric time. This way, lunar standard time can be converted with Earth time and Coordinated Universal Time (UTC), meeting the definition criteria set by the International Bureau of Weights and Measures that lunar standard time must have traceability to Earth time.

However, the conversion between lunar coordinate time and barycentric time is determined by the moon's extremely complex multi-body motion and the dynamic gravitational field exerted by all celestial bodies in the solar system. Existing conversion formulas internationally use series approximation theory, leading to low calculation accuracy, complicated processes, and lack of directly usable products.

To this end, the research team used the most accurate orbital information of the sun, planets, main belt asteroids, and Kuiper belt objects to achieve precise conversion between lunar coordinate time and barycentric time, with cumulative errors not exceeding 1/20000000 seconds even after 1000 years. The research team further developed an end-to-end software package product, allowing users to obtain precise conversion results of lunar coordinate time with just one operation.

The related research findings have been published in the journal Astronomy & Astrophysics.

Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said that lunar time measurement is becoming a real engineering need, no longer something that can be handled individually as before based on Earth time.

He pointed out that microsecond-level errors in spacecraft navigation systems could have significant impacts, affecting calculations on a minute-scale time frame. "If you want to use a GPS-like system on the moon - we may need it within a few years, especially for precise landing locations, you need to find a way to solve this problem," he said.

McDowell said that although the United States is also working on similar projects, he hasn't heard of any directly usable "lunar time software." He said, "This reflects China's emphasis on the moon and its openness in sharing lunar-related research."

The South China Morning Post stated that in the past, the number of lunar missions was very limited, and time errors were almost "irrelevant," with engineers able to correct each mission individually according to Earth time as needed. But as lunar exploration has become a focus in the global space industry, there will be more and more spacecraft and even crewed spacecraft heading to the moon, making it difficult to rely on temporary solutions to address error problems.

In addition, establishing a time standard is not only important for coordinating lunar missions but also a symbol of political influence. The South China Morning Post cited an example, stating that in 1884, Britain decided to set the location of the Greenwich Observatory as the prime meridian benchmark, not only for convenience but also reflecting Britain's dominant position in the world's maritime, trade, and scientific fields at that time.

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Original: toutiao.com/article/7594487121357734410/

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