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Science & Tech.
Mahesh

22/08/24 09:30 AM IST

Time standard for the Moon

In News
  • The International Astronomical Union recently proposed the establishment of a timekeeping standard for the Moon.
Earth's Time standard
  • Most of the clocks and time zones — a geographical region which uses the same standard time — of the world are based on Coordinated Universal Time (UTC), which is set by the International Bureau of Weights and Measures in Paris, France.
  • UTC is essentially an internationally agreed upon standard for world time.
  • It is tracked by a weighted average of more than 400 atomic clocks placed in different parts of the globe.
  • Atomic clocks measure time in terms of the resonant frequencies — the natural frequency of an object where it tends to vibrate at a higher amplitude — of atoms such as cesium-133.
  • In atomic time, a second is defined as the period in which a caesium atom vibrates 9,192,631,770 times.
  • As the vibration rates at which atoms absorb energy are highly stable and ultra-accurate, atomic clocks make for an excellent device for gauging the passage of time.
  • To obtain their local time, countries need to subtract or add a certain number of hours from UTC depending on how many time zones they are away from 0 degree longitude meridian, also known as the Greenwich meridian.
  • If a country lies on the west of the Greenwich meridian, it has to subtract from the UTC, and if a country is located on the east of the meridian, it has to add.
Need of time standard for moon
  • UTC, however, cannot be used to determine time on the Moon. That is because time on the Moon flows differently than it does on the Earth.
  • A fundamental aspect of nature in the Universe is that time is not absolute.
  • That seems crazy to us on Earth as our experience of time is that it just constantly ticks by. But if you travelled to the Moon, your clock would be ticking slightly faster than if you had stayed on the Earth.
  • As there is less gravity on the Moon, time ticks slightly faster there relative to the time on the Earth.
  • In other words, for someone on the Moon, an Earth-based clock will appear to lose on average 58.7 microseconds per Earth day with “additional periodic variations.
  • The discrepancy may seem small but it can create problems for situations such as a spacecraft seeking to dock on the Moon, data transferring at a specific time, communication, and navigation.
Lunar time standard
  • The specifics for creating a time standard for the Moon are not clear yet.
  • Like on the Earth, atomic clocks can be deployed on the lunar surface to set a time standard.
  • There will be a need to place at least three atomic clocks on the lunar surface that will tick at the Moon’s natural pace, and whose output will be combined by an algorithm to generate a more accurate virtual timepiece.
  • These clocks have to be placed on the Moon at different locations since the Moon’s rotation and even local lumps of mass, called mascons, beneath the crust of the Moon affect the flow of time ever so slightly.
  • Mascons or mass concentrations are so dense that they alter the Moon’s local gravity field.
  • These effects are minor but the output from these clocks can be synthesised to give the Moon its own independent time, which can be tied back to UTC for seamless operations from Earth as well.
  • Even on Earth, atomic clocks have been placed at different locations or rather latitudes.
  • These clocks tick at different rates due to changes in Earth’s rotational speed varying from the Equator to the poles, which also affects time.
  • The planet rotates faster at the Equator than it does at the poles as it is wider at the Equator.
Source- Indian Express

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