Email or username:

Password:

Forgot your password?
All posts Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ's posts Post Back to profile
Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ

I keep seeing the news about lunar time presented as β€œthe Moon is getting its own time zone." What's actually happening is the Moon is getting its own time *standard*. The problem being solved is that time passes slightly more quickly on the Moon compared to Earth (due to General Relativity) and so the Moon needs its own time standard for precise measurements and navigation. UTC is the time standard for measuring time on Earth, and LTC is being created for the Moon.

#GeneralRelativity #time

5 April at 17:02 | Open on mastodon.social
22 comments
FoolishOwl
Michael Bradley

@dgoldsmith Given that UTC stands for Coordinated Universal Time (at least in English), it seems like it's in need of a renaming. Perhaps Coordinated Terrestrial Time?

I wonder if this will continue for other important celestial bodies? I wouldn't be surprised if at least Mars got its own time standard codified. Wikipedia mentions an "MTC", but only as a "proposed" standard based on Mars's orbit instead of atomic clocks.

5 April at 20:13 | Open on mstdn.ca
Michael Bradley

@dgoldsmith Although it feels a little impractical to keep creating new standards for every celestial body we visit, perhaps we need a new standard somehow independent of general relativity... how about "Stardate"? πŸ––

5 April at 20:17 | Open on mstdn.ca
Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ

@michaelbradley I don't think we're going to be visiting that many celestial bodies, so I'm not worried about that.

You still need to define the relationship between the various time standards. UTC is basically "stardate" already; LTC will be defined relative to UTC.

5 April at 20:25 | Open on mastodon.social
pglpm

@michaelbradley @dgoldsmith
There is such a time (obviously based on general relativity), at least for the whole Solar System neighbourhood. It's called Barycentric Coordinate Time (TCB). A good paper to read about these standard times is Petit's geodesy.unr.edu/hanspeterplag/

6 April at 23:39 | Open on emacs.ch
Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ

If you're curious why time passes more quickly on the Moon, it's this:
en.wikipedia.org/wiki/Gravitat Because Earth's gravity is higher, there’s more time dilation than on the Moon (by about 58.7 microseconds per day, or 2.144 seconds per century).

One way to think about it is that the local neighborhood of spacetime for someone standing on the Earth's surface is boosted (β€œtilted”, in a 4D sense) relative to that for someone far away from any massive body.

#GeneralRelativity #time

If you're curious why time passes more quickly on the Moon, it's this:
en.wikipedia.org/wiki/Gravitat Because Earth's gravity is higher, there’s more time dilation than on the Moon (by about 58.7 microseconds per day, or 2.144 seconds per century).

One way to think about it is that the local neighborhood of spacetime for someone standing on the Earth's surface is boosted (β€œtilted”, in a 4D sense) relative to that for someone far away from any massive body.

6 April at 19:26 | Open on mastodon.social
Ian Bradbury

@dgoldsmith - that’s a great link, after reading the page twice I’m sure I don’t fully appreciate/understand the topic.

However this line has zapped my brain….. β€œRelative to Earth's age in billions of years, Earth's core is in effect 2.5 years younger than its surface”

8 April at 21:52 | Open on considerate.social
Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ

@ianbradbury The planet orbiting the black hole in β€œInterstellar" is an extreme example (if you've seen that, or know the plot).

8 April at 22:18 | Open on mastodon.social
Ian Bradbury

@dgoldsmith - yes, of course, I forgot about that. Great film.

9 April at 6:32 | Open on considerate.social
Adam Shostack :donor: :rebelverified:

@dgoldsmith I'm really not sure that replacing MET is needed just yet, but it's a very optimistic move.

(MET, as you probably know, is mission elapsed time, which has been fine and will remain fine until we have satellites around the moon or other long term presence.)

8 April at 21:22 | Open on infosec.exchange
Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ

@adamshostack I don't think it's really needed for the function that MET serves, but more to have a standard to coordinate multiple spacecraft/experiments/instruments/etc. Yes, it's a bit forward-thinking.

8 April at 21:55 | Open on mastodon.social
Adam Shostack :donor: :rebelverified:

@dgoldsmith Exactly. If you need to coordinate stuff, that's exciting ... times.

Sorry. I couldn't resist. :blobangel:

8 April at 22:02 | Open on infosec.exchange
Dr. Dan Killam

@dgoldsmith yeah, way more amazing and deeper than a time zone honestly

8 April at 21:29 | Open on scicomm.xyz
Attila Kinali

@dgoldsmith You seem to be knowledgeable on this topic. Could you explain why we do not just compensate for gravitational red shift on the moon the same way we do for the various NMI labs that are at different altitudes and thus run at slightly different rates? Why do we need LTC when just using UTC with the correct definition of the second (i.e. defined at zero gravitational field) would be sufficient?

8 April at 23:30 | Open on society.oftrolls.com
Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ

@attilakinali Here is the document:
whitehouse.gov/wp-content/uplo

and in particular, the goals:
1. Traceability to Coordinated Universal Time (UTC);
2. Accuracy sufficient to support precision navigation and science;
3. Resilience to loss of contact with Earth; and
4. Scalability to space environments beyond the Earth-Moon system

It is still linked to UTC, as far as I can tell (bullet 1).

@attilakinali Here is the document:
whitehouse.gov/wp-content/uplo

and in particular, the goals:
1. Traceability to Coordinated Universal Time (UTC);
2. Accuracy sufficient to support precision navigation and science;
3. Resilience to loss of contact with Earth; and
4. Scalability to space environments beyond the Earth-Moon system

8 April at 23:39 | Open on mastodon.social
TheDarcBird
Winter Trabex

@dgoldsmith

Wait, time passes more quickly on the moon? How does that work? Is it something influenced by planetary gravity?

9 April at 5:32 | Open on newsie.social
Debbie Goldsmith πŸ³οΈβ€βš§οΈπŸ³οΈβ€πŸŒˆ

@trabex It's called β€œgravitational time dilation" (en.wikipedia.org/wiki/Gravitat). Time passes more slowly in a gravitational field. The stronger the gravity, the slower time passes. It's a consequence of general relativity. So time passes more slowly on Earth than on the Moon because Earth's gravity is stronger.

On Earth, time passes more quickly at the top of a mountain than at sea level. This effect has been measured.

9 April at 5:37 | Open on mastodon.social
Go Up