How future astronauts will measure time on the moon and elsewhere in space
The North American Space Agency (NASA) has been instructed by the United States of America government's Office of Science and technology Policy (OSTP) to develop and implement a "unified lunar time standard", to be referred to as Coordinated Lunar Time (LTC) or "Moon Time", in preparation for the planned return of humans to the moon in September 2026, under its Artemis program.
Time management here on Earth is based on the internationally-recognized 24-hour UTC (Co-ordinated Universal Time) system, often referred to simply as Universal Time. This system, officially adopted in 1963, relies on a vast system of atomic clocks in numerous locations around the world that measure the changes in the state of selected atoms, thereby creating an average that establishes an exact time.
Atomic clocks are based on the frequency with which atoms oscillate (vibrate); counting the number of times they move back and forth, which, in turn, establishes a time reference. Since the atom oscillations occur with extreme accuracy, the same number of oscillations occur within a particular amount of time. The LTC system will require atomic clocks on the moon, and on any other moons, asteroids, or planets which humans colonize.
TIME ZONES
The current global UTC system divides our planet into 24 hourly time zones that a traveler would experience while travelling around the globe. Each time zone incorporates approximately 30 degrees of global longitude, although the exact time zone lines tend to zig-zag somewhat depending on topography and international politics.
Except for some jet-lag that some travelers experience while crossing between several time zones, this system appears to function reasonably well, even in areas where the demarcation between two adjacent time zones is the center of a street or a national boundary, with the time on one side of the street or boundary being either an hour ahead or behind that on the opposite side of the street or boundary. There are a few locations on the globe where the time zone differentials are only by a half-hour.
TME MANAGEMENT
During the 1960s and '70s, time-management for the lunar missions between the Earth and the moon, and for the space probes to the solar system's other planets, followed the time zone of the area from which the spacecraft was launched, with the on-board clocks and computers of the spacecraft, and the wristwatches of the astronauts, set accordingly.
The time-management systems of the primary central command stations (e.g., Houston Space Center for NASA'S Apollo lunar missions) monitoring the launches and subsequent flights, landings, and returns, etc. of these crafts, maintained a synchronization with the spacecraft's on-board clocks and computers in order to accurately monitor the spacecraft, and to facilitate the transfer of required data between themselves and the spacecraft in a timely and accurate manner.
As these lunar missions were of a relatively short duration of only several days or weeks, the existent UTC
time-management system worked reasonably well, and still does. Countries currently sending missions to the moon and elsewhere use their own time zones.
BACK TO THE MOON
However, as humans return to the moon in the coming decades, with the goal of establishing and manning permanent scientific bases and commercial, resourceextraction facilities on the moon, and possibly on distant asteroids and the moons of some of the outer solar system planets, time-management will take on a different perspective; time on the moon (and elsewhere in space) is different from Earth time.
To understand this new perspective, we have to have a basic grasp of "gravitational time dilation", a theory put forth by the famous Germanborn theoretical physicist, Albert Einstein (1879-1955) in 1907, as part of his Theory of Relativity. This theory deals with the effect of gravity on space and time, and the actual difference in elapsed time between two events as measured by two different observers situated at varying distances from a gravitating body.
He essentially theorized that time would move more slowly for someone situated on a body with a stronger gravity, and quicker for someone on a body with less gravity. How much gravity a person is experiencing is a factor that influences how quickly time appears to move. The moon has one-sixth the gravity of Earth; as a consequence, time passes more quickly on the moon than on Earth. As mentioned above,
Earth time is determined by atomic clocks situated around the planet.
ATOMIC CLOCKS
Atomic clocks on the moon would oscillate at a different rate than atomic clocks on Earth, approximately 58.7 microseconds faster per Earth day, with other periodic variations also causing lunar time to drift further away from Earth time. While this figure might seem minute on the face of it, the relativistic effects, if not accounted for, could result in errors and/or failures in the synchronized communication and data transfer between Earth and any lunar-based assets or orbiting satellites.
Events that appear simultaneously on Earth (e.g., the start of a radio signal) would not appear simultaneously on the moon; such time differences could lead to problematic issues respecting the mapping of the lunar surface, the orientation and height of orbiting satellites, and spacecraft orbital inserts and landings, with the potential for dire consequences.
As missions to the moon and systems beyond increase in both number and complexity in the coming decades, it becomes imperative that data management and transfer systems function in a manner and to a degree which ensures that there are no errors. Without a unified LTC, future international missions, whether scientific or commercial, would be difficult to coordinate.
Establishing a LTC would create a system of timekeeping which would serve as a benchmark for all spacecraft and satellites, the operation and safety of which, by their nature, require extreme precision, as well as the logistics and viability of future space commerce.
THIS WEEK'S SKY
Mercury (mag. +5.4, in Pisces - the Fish) having just completed inferior conjunction, is not observable, at only 5 degrees separation from the Sun.
Venus (mag. -3.9, in Pisces) is not readily observable, as it sits right on the eastern horizon at dawn. It might be possible, with a clear sky and an unobstructed south-southeast horizon, to see both Mars (mag. +1.2, in Aquarius - the Water-bearer) and Saturn (mag. +1.1, in Aquarius) low in the southeast, pre-dawn sky.
Jupiter (mag. -2.0, in Aries - the Ram) will be visible around 8:20 p.m., 16 degrees above the western horizon as the sky darkens, before sinking towards the horizon and setting shortly after 10 p.m.
Uranus (mag. +5.8, in Aries) sits just above Jupiter in the western evening sky.
Neptune (mag. +8.0, in Pisces) is not observable, as it sits 5 degrees below the southeast horizon at dawn.
ON THE LOOKOUT FOR OTHER PLANETS
How many of you thought to look for, or photograph, any of the above planets (excepting Uranus and Neptune) while observing the April 8 total solar eclipse?
At eclipse totality, with a clear, cloudless sky, Saturn and Mars (sitting below Saturn) were visible low above the western horizon, Venus shone brightly about halfway between these two planets and the eclipsed Sun, with Mercury directly above the Sun, and Jupiter a bit further up and to the left. Also, possibly visible under perfect seeing conditions, and with the correctly-filtered telescope and/or camera, was Comet 12P/pons-brooks to the right of Jupiter.
If you captured a clear photo of the totally eclipsed Sun, you might want to check and see if you also captured some/all of the planets mentioned above, and, perhaps, even the comet.
Until next week, clear skies.
Glenn K. Roberts lives in Stratford, P.E.I., and has been an avid amateur astronomer since he was a small child. He welcomes comments from readers at glennkroberts@gmail.com.