What Time Is It on the Moon?

If all goes well, we'll be sending astronauts back to the Moon in just a couple of years. And scientists have a lot to figure out before then, including the answer to a seemingly simple question: What time is it up there?

Hosted by: Savannah Geary (they/them)
----------
Support us for $8/month on Patreon and keep SciShow going!
Join our SciShow email list to get the latest news and highlights:
----------
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever: Odditeas , Garrett Galloway, Friso, DrakoEsper , Kenny Wilson, J. Copen, Lyndsay Brown, Jeremy Mattern, Jaap Westera, Rizwan Kassim, Harrison Mills, Jeffrey Mckishen, Christoph Schwanke, Matt Curls, Eric Jensen, Chris Mackey, Adam Brainard, Ash, You too can be a nice person, Piya Shedden, charles george, Alex Hackman, Kevin Knupp, Chris Peters, Kevin Bealer, Jason A Saslow
----------
Looking for SciShow elsewhere on the internet?

#SciShow #science #education #learning #complexly
----------
Sources:

[g.m.]

The local Lunar time should be called the Lunatic

[maxwelljennings]

happy moon landing day! around 55 years ago, the first human landed on the moon!

[Ice_Karma]

I'm a _huge_ metrology (the science of measurement) and horology (the science of timekeeping) nerd, and this is *_AWESOME!!_*

[salaufer]

As a software engineer, I support violent resistance against the addition of any new time zones. My life would be so much easier if everyone just used UTC.

[deathsyth]

"What time is it?"
"Time to get a new watch."

[robspiess]

Fun fact: Seem strange that "Coordinated Universal Time" is called "UTC" and not "CUT"? That's cause, along with the French "Temps Universel Coordonné" (which would have been "TUC"), "UTC" was chosen as a compromise to be the same abbreviation for all languages.

[ViralHijack]

They should probably change Coordinated Universal Time to Coordinated Earth Time if they are going to expand to other planets.

[aarnavlovesnature]

Thanks for explaining! Your channel motivates many people to become scientists, even at the lowest level, it makes a difference.

[Kezrek]

Is anyone else excited for humans' return to the moon?? I'm totally jazzed about this

[onlybecauseoftime]

If we went by cycles of “day” and “night” like on earth, the Moon takes a whole month to complete one rotation. This means that lunar day and night are each about two Earth weeks long. In that way, moon time would be very slow!

[Rubrickety]

Matt O'Dowd has trained me that when the word "spacetime" get spoken, the video is about to end. Not here!

[BenjaminKlahn]

A martian time standard is easy. It's only a little different from earth so you simply add 37 minutes to the normal 24 hour clock and just let people get some extra sleep.

[aeromoe]

It's 110F outdoors where I am right now and she's wearing a sweatshirt 😂😂 And then the advert comes on and she's in a jumper! 😅😅

[TerryBollinger]

In a 1911 lecture, Einstein defined a procedure for creating a self-consistent definition of time in a large volume of space: Select a single unaccelerated clock as your master clock. Next, position (or find) identically constructed clocks throughout a large volume of space while ensuring those clocks remain motionless relative to the original clock. His final step was to do a "handshake" synchronization of those motionless clocks with the original master clock, with lightspeed delays considered.

The result is a large volume of space instrumented with clocks that share the same initial dial settings and tick at the same rate. Einstein's point was remarkably practical since he noted that until you do this procedure using physical (versus abstract) clocks, the interchangeability of space and time makes it impossible to find an unambiguous set of space and time coordinates for any event relative to the master clock. He noted that a physicist can only collect meaningful data once implementing some version of this procedure.

For systems _not_ at rest relative to your master clock, Einstein required you to read their times only when they pass by and "touch" one of your previously synchronized clocks. This direct contact is vital because it eliminates space-time ambiguity. It is, for example, why particles in accelerators always show time as passing slower since the entire accelerator is synchronized to the clocks of physicists.

Notably, this procedure guarantees that _all_ clocks moving relative to the master clock show time passing slower than the master clock and its subordinate clocks. This causes no temporal paradoxes because two parameters are in play, not just one: How fast the moving clocks tick off time, which is always slower than the master clock, and the time setting (dial positions) of the moving clock, which increases with distance traveled.

Thus, if you travel to the Andromeda galaxy close to lightspeed, every clock you pass along the way ticks slower than yours. The catch is that the current time setting of each such clock _changes_ as you travel forward through space. Thus, if you travel to the Andromeda Galaxy, every clock you encounter at rest relative to the Milky Way or Andromeda runs at a snail's pace relative to the clocks in your spaceship. However, you also notice that the farther you go, the farther into the future these clocks appear to be set. By the time you reach your destination, every slow clock you encounter is set 2.5 million years ahead of the clocks in your ship, so a delay of a second or two due to the Andromeda clocks running slower makes very little difference.

This _age gradient_ effect only appears when smaller groups of Einstein-synchronized clocks move through vastly larger sets of previously synchronized clocks. Both tiny particles within huge accelerators and tiny spaceships traveling between galaxies meet this criterion and thus encounter age gradients as they travel. Such age gradients also explain the twin's paradox since one twin stays in the larger clock frame and thus encounters no forward resetting of time per light year traveled.

Since this was before General Relativity, Einstein did not address the impact of gravity on defining a singular time standard. The main effect of adding gravity is to force the use of clocks that do _not_ tick a the same rate. For example, suppose your master clock is on Luna. In that case, its subordinate clocks in the deeper gravity well of Earth must run a bit faster than normal to maintain handshake synchronization with the master clock on Luna. The faster-running clocks become a stark warning that gravitational time dilation is not relative in the same fashion as velocity time dilation.

I recommend using Einstein's concept of creating an explicit network of UTC-synchronized clocks, with the addition of variable-speed clocks to account for irreversible gravitational time dilation. All such clocks would treat Earth's UTC master clock as supreme, even if they have to run a bit fast or slow. The second part would be using local-physics-only clocks that track local time. Combined with the UTC clocks, these dual clocks would convert time dilation effects into absolute, non-relative numbers. The Luna UTC master clock would appear to be running a bit slow by Luna standards, while the second Luna Physics clock (which could be virtual, nothing more than a multiple of the UTC one) would give the Luna-rate time needed for physics work.

For travelers, the "it's all relative" non-answer doesn't work and is already not what GPS satellites do. (I keep meaning to look that up. They necessarily use some variant of age gradients, even if only labeled as "corrections" for satellite distance traveled.) A dual system is again needed. A fast-moving spaceship would have a UTC clock time that speeds up as the ship moves faster and a spaceship-frame-only clock that defines its local physics. While this dual-clock approach destroys the mystery of claiming everything is relative, it also makes causality easier to track and displays explicitly when accelerated systems become asymmetrically time-dilated. Age gradients calculate how much time is lost during travel -- that is, how far you move into the future per kilometer traveled.

[jessicatymczak]

How do you tell that clocks on the moon are crazy?

Because they lunar ticks

[Wolfie]

Fun Fact: The moon landing technically happened on both July 20th and July 21st

[Brownyman]

Dawes: How old are you?

Diogo: Nineteen, I think. Earther years.

Dawes: Even our sense of time comes from them.

[brian]

It doesn’t seem so difficult….
Since we know the difference between moon and earth time “velocity” (for want of a better term) just apply the conversion factor.
It will require an atomic clock in order to have time measurements accurate enough for it to make a difference anyway, so to me it seems very straightforward.
What am I missing?

[alexrogers]

Given the title question this really should have opened with the Vsauce music

[BillySugger]

There is such a strong case for using UTC. Almost every human alive or has ever lived, spends and spent their entire lives on Earth. And we evolved in a 24h day regime. Nowhere else does a 24h day correspond to any celestial time standard. So there is a case for a local time on each planet or other body, relative to some celestial phenomenon like day and night on that body, just like we have local time zones around the Earth corresponding to the day-night cycle here, and a universal time for synchronising events between bodies. The latter makes sense to be UTC, and can be derived by exchanging time signals between Earth and the body rather like computers do with the Network Time Protocol (NTP) on Earth. Except allowance would have to be made for light travel time. Either distant bodies lag by their light time from Earth (so events are considered simultaneous when a light signal passes between them), or the distant body is delayed by their light time from Earth, caving to the illusion of simultaneity in Classical physics.