Researchers at NASA’s Jet Propulsion Laboratory (JPL) have calculated a new system for measuring lunar time. While not needed for most people’s daily schedules, establishing time on the lunar surface as compared to time on Earth is vital to realizing a permanent human presence on the moon.
Earlier this year, the Biden administration directed NASA to begin work on calculating a Coordinated Lunar Time (LTC). But thanks to the complexities of gravitational force and relativity, clocks in the Artemis Base Camp will move differently than those back home. This means entirely new clocks designed to run as accurately and reliably as possible. According to a study slated for publication in the journal, Physical Review D, the key to the new system is relativistic time transformations, better known as “time dilation.”
“Our work is conceptually aligned with the broader goals of time standardization in cislunar and deep-space environments,” JPL astrophysicist and study co-author, Slava Turyshev, tells Popular Science. “These are foundational for future lunar missions requiring sub-nanosecond synchronization for navigation, communication, and science operations.”
[Related: NASA is designing a time zone just for the moon.]
A single second’s length is experienced differently depending on gravitational force and relative velocity. An astronaut on the moon looking at an Earth-based clock, for example, would see it lose about 56 microseconds per terrestrial day. Although that amount may sound minuscule, it adds up—and that can pose major problems when multibillion dollar lunar missions and astronaut lives are on the line.
“These systems are crucial for supporting operational efficiency, scientific endeavors, and future commercial activities on the Moon,” Turyshev’s team writes in their study. “Existing Earth-centric frameworks are inadequate for these demands, necessitating the development of an independent lunar coordinate and time system.”
As Universe Today explains, JPL researchers adapted the principles of relativity used in Earth timekeeping for a lunar environment. These included factors such as weaker lunar gravity resulting in faster clock tick rates, periodic time variations during the moon’s orbit, and “local gravitational anomalies” known as mascons which influence time on the moon. They then turned to detailed data amassed by NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Launched in 2011, the decade-long GRAIL program used a pair of satellites to map the moon’s surface, as well as measure its gravitational field. The team also factored in information gathered from the Lunar Laser Ranging (LLR) project that measured orbital distances between the moon and Earth down to the millimeter.
After some extremely dense calculations and physics analysis, Turyshev and his collaborators determined that lunar time drifts ahead of time on Earth by roughly 56 microseconds per day, depending on the Moon’s orbit. Although these semiregular oscillations only measure around 0.47 microseconds every 27.5 days, the tiny discrepancies can make a huge difference when calculating safe rocket landings, mission schedules, and more.
The implications of a Lunar Timescale (LT) and a Lunicentric Coordinate Reference System (LCRS) also go far beyond the initial Artemis missions. Any permanent settlements on the moon will require a dedicated time system to allow for greater autonomy. But if all goes according to plan and the massive logistical, financial, and scientific hurdles are cleared, don’t expect to need to calculate complex time zone shifts like here on Earth.
“Offering a direct conversion like ‘12PM EST = X PM on the Moon’ isn’t straightforward due to the relativistic drift between terrestrial time (TT) and lunar time (TL),” says Turyshev. “… However, if we simplify things for illustration, 12PM EST on Earth would roughly correspond to 12PM plus a tiny drift on the Moon, depending on the specific mission timeline.”
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