The National Aeronautics and Space Administration (NASA) of the United States has officially embarked on the task of establishing a standard time for the Moon, known as "Lunar Coordinated Time" (LCT). This time system is expected to be completed by the end of 2026.
Image Source: Dima Zel
The reason for completing this work by the end of 2026 is that the US Artemis III mission plans to send astronauts to the vicinity of the lunar South Pole no earlier than 2026, at which time American astronauts and spacecraft can use the moon's time system.
So, the interesting question is, why do we need to create a standard lunar time specifically for this moon landing, when previous Apollo moon missions didn't have lunar standard time and seemed to do just fine?
During the Apollo moon landings, indeed, lunar time was not used. The astronauts' watches were synchronized with the time zone of Houston, where Mission Control was located.
However, lunar standard time is indeed necessary, even indispensable. The main reason is that time plays the most crucial role in modern technology, and the passage of time on the moon is different from that on Earth. This can lead to errors or the inability to carry out certain tasks.
Image Source: Pixabay / Christy Miller
Clocks Tick Faster on the Moon
Due to tidal locking, one side of the Moon always faces us, leading some to believe that there are no day-night changes on the lunar surface.
In reality, the Moon does rotate on its axis, and the Sun illuminates different areas, creating periods of daylight and darkness. However, due to tidal locking, its rotation matches its orbit around Earth, happening at a snail's pace, with days and nights lasting about two weeks each.
Earth's 24-hour day is defined by the cycle of day and night, which doesn't quite fit the Moon. This is one reason for establishing lunar standard time, though not the primary one.
The main reason is that the Moon has much less gravity than Earth, causing time to pass faster there than on Earth.
If spacecraft or astronauts on the Moon were to use Earth's standard time, their clocks would run ahead by about 58.7 microseconds each day (I'll explain later why this discrepancy is unacceptable), a phenomenon known as time dilation.
Einstein was the first to discover this, initially believing that the speed of light was constant, leading to his formulation of the theory of special relativity.
Einstein's explanation for the constancy of the speed of light was that it remains constant in all reference frames; no matter how fast you're moving, the speed of light relative to you remains unchanged.
Image: The arrow shot from moving train A appears faster than the stationary B, but the speed of light remains constant.
Moreover, if two individuals are moving simultaneously, regardless of the speed difference between them, the speed of light remains the same relative to both. For instance, if you're moving at 99% of the speed of light and another person at 1%, the speed of light remains constant for both of you.
This is challenging to grasp and goes against intuition, but Einstein's genius lies in finding the explanatory solution. He proposed that time undergoes changes during motion.
Your time and the other person's time are not the same. If your speed is faster, time elapses slower for you. Therefore, you perceive the speed of light the same way as the other person.
This is the essence of the theory of special relativity, which explains the time dilation with velocity, a concept that has been verified through observational experiments.
Image Source: NASA
Due to the faster speed of the space station, the atomic clock onboard records slower time. Additionally, scientists have observed time dilation at speeds slower than 10 meters per second using atomic clocks.
Following the theory of special relativity, Einstein began contemplating gravity. He used the relative flow of time to explain the essence of gravity, leading to the development of the theory of general relativity.
We don't necessarily need to understand the specifics of general relativity; we just need to know that gravity also causes time dilation. Moreover, the greater the gravitational force you experience, the slower time passes for you.
This has been demonstrated through experiments with atomic clocks showing time dilation due to gravity even with just a 1-meter height difference on the Earth's surface. These experiments, along with the previously mentioned "time dilation at speeds slower than 10 meters per second," were completed by 2010.
The gravitational force on the Moon is different from that on Earth, resulting in a different passage of time. Time dilation can be calculated using formulas. I found a ready-made answer: On the Moon, each day is about 58.7 microseconds faster than on Earth—equivalent to roughly 0.02 seconds per year.
Now, the question arises: Is it really necessary to establish an independent timekeeping system for the Moon just to account for this 0.02-second discrepancy per year?
Why is synchronization so important?
If you're a frequent computer user and have ever encountered internet connectivity issues, you've likely had to synchronize your time.
I've personally done this many times, especially in the days when computers weren't as ubiquitous. Whenever the internet failed to connect, simply syncing the computer's time would often resolve the issue.
To be honest, I never knew the reason behind it or bothered to understand why syncing the time could get me back online. But for the sake of this article, I delved into it a bit.
Essentially, for the security of the internet, to safeguard our personal privacy, and to protect our personal computers from third-party attacks when accessing servers, there's a system called the public key certificate system. Each time you visit a website, it establishes a remote identity certificate, thereby enhancing security.
The crux of this public key certificate system lies in time. If your computer's time isn't synchronized, it can't properly establish this certificate, and consequently, you won't be able to access external resources.
In addition, many online transactions now incorporate a concept called timestamping to enhance security. This concept ensures that data existed in its entirety at a specific point in time, thereby preventing third-party tampering with the data afterwards.
In essence, if you're using internet-related services on the moon, time synchronization is crucial. Otherwise, data errors may occur, jeopardizing security.
You might wonder, are Beijing time and other time zones the same?
While people in different regions set their clocks based on their position on Earth - known as time zones - all time zones globally are defined based on Coordinated Universal Time (UTC).
Coordinated Universal Time (UTC) is established by the International Bureau of Weights and Measures located in Paris, France. It is created using a combination of atomic clocks from around the globe, which send their time to the Bureau International des Poids et Mesures (BIPM) in Paris to ensure synchronization of clocks in every country. This forms the foundation of the global internet.
However, the internet and online transactions are not the only things reliant on precise timekeeping. Of paramount importance is the global navigation system, which also relies on time. This is especially critical during lunar missions.
Navigation is satellite-based, and satellites determine your position based on time. Satellite signals arrive slightly later than the current time on the ground by about a fraction of a second. This time differential can be utilized with remarkable precision to determine a person's location on the Earth's surface.
For accurate positioning in satellite navigation, errors must be minimized to the nanosecond level. As mentioned earlier, there is a time discrepancy of 58.7 microseconds between the Moon and Earth. If Coordinated Universal Time were used on the Moon, significant positional deviations would occur.
Image Source: NASA
Previous lunar missions were rudimentary and single-focused, lacking the sophistication required for long-term lunar operations. However, lunar missions in the 21st century have evidently transitioned into a phase aimed at sustained lunar presence, necessitating the establishment of a standard lunar time. Some scientists have even proposed the creation of standardized time systems for Mars and other celestial bodies.
However, a crucial question remains regarding lunar standard time: who should establish or lead this effort?
In fact, it's not just NASA undertaking this endeavor; the European Space Agency (ESA) has also been involved.
Given that each entity has its own priorities and visions, the task of creating lunar standard time has become quite complex.
