The Lunar Standard Time

by Joao Moreira

Some time ago, quite by accident, I stumbled upon this website: The Lunar Clock. Specifically, it is a proposal for a Lunar Standard Time. I was baffled. I had no idea that such a thing existed but, in retrospect, it shouldn’t be that surprising.

The Lunar Standard Time (LST) was first proposed by Rudolph N.J. Draaisma, and is now maintained by, a non-profit organization. Why did they bother? Well, for the convenience of future moon colonists of course! While that may not be happening very soon, I believe that at some point we will have people there and they will certainly appreciate a calendar that is not based on the orbit of another planet.

So, here is the breakdown of the Lunar Calendar1:

  • The lunar year consists of 12 lunar days
  • A lunar day is divided into 30 lunar cycles
  • Each lunar cycle has 24 moon-hours
  • 1 moon-hour has 60 moon-minutes
  • 1 moon-minute has 60 moon-seconds

As you can see, it is structurally very similar to the standard earth calendar. The reason is that, although you are going to another planet, you want some comfort from back home (not unlike immigrants in a foreign country).

LST actually has a logic to it. The Moon experiences about 14.77 (earth) days of sunlight followed by 14.77 days of night so a lunar day lasts about 29.53 earth days – one earth month. Hence, the division of a lunar day into 30 lunar cycles. To get a 24-hour clock from this you define the moon-second as 29.53/30 = 0.984 seconds. The rest of the calendar follows from that:

  • 1 Lunar year <-> 354 Earth days
  • 1 Lunar day <-> 29.53 earth days
  • 1 Lunar cycle <-> 23 hours 27 mins
  • 1 moon-hour <-> 59 mins
  • 1 moon-minute <-> 59 secs
  • 1 moon-second <-> 0.984 secs

Like the “Earth-months”, lunar days have special names too. Perhaps not that surprisingly, they were named after the first people to walk on the moon!

  • Day 1 Armstrong
  • Day 2 Aldrin
  • Day 3 Conrad
  • Day 4 Bean
  • Day 5 Shepard
  • Day 6 Mitchell
  • Day 7 Scott
  • Day 8 Irwin
  • Day 9 Young
  • Day 10 Duke
  • Day 11 Cernan
  • Day 12 Schmitt

Yup, all men, all American. The names also hint at the beginning of LST: Year 1, day 1, cycle 1, 00:00 hours (obviously?) marks Neal Armstrong’s “small step” in the Sea of Tranquility. So, right now on the moon it is:

That little inverted triangle is the Nabla symbol, widely used in physics and mathematics to represent vectorial differential operations. According to the website, they choose to use the nabla because it is also the “ancient symbol representing Luna – the feminine principle” (I couldn’t find a source for this).

So there you have it. If you ever decide to move to the moon you now have a handy way to mark the time (which you will spend doing what exactly?).

Expect a post on the MST in 20 to 30 years’ time upon the occasion of the first manned Mars landing.

1The lunar calendar defined here is unrelated to the existing earthly lunar calendar.