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Moon Watch

When the moon hits your eye, like a big pizza pie, it's about half ten
  (+45, -3)(+45, -3)(+45, -3)
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Place two large aluminium-foil spheres in orbit around the Moon with orbital periods of 1 hour and 12 hours, respectively.
FlyingToaster, Mar 10 2009

Sir Patrick Moore http://en.wikipedia.../wiki/Patrick_Moore
Gods gift to astromony [eight_nine_tortoise, Mar 10 2009]

orbit calculator http://www.calctool...ronomy/planet_orbit
eliminates cock ups [DenholmRicshaw, Mar 11 2009]

Zulu time http://hurricanes.noaa.gov/zulu-utc.html
[Klaatu, Mar 17 2009]

Giant date and time display on the Moon
"Moon Watch" is pretty much my favourite idea on HB, but just realised some credit needs to go to WcW (see first anno in linked idea) [xaviergisz, Aug 07 2011]

42 http://gpu.sourceforge.net/9billion.php
[mouseposture, Aug 07 2011]

NASA Considers Putting an Asteroid Into Orbit Around the Moon http://science.slas...bit-around-the-moon
[xaviergisz, Jan 05 2013]

[link]






       Why?
zeno, Mar 10 2009
  

       the real question is when?
k_sra, Mar 10 2009
  

       High Time?
phoenix, Mar 10 2009
  

       Lunartick.
wagster, Mar 10 2009
  

       You are forgetting the Sir Patrick Moore factor. Any moon ideas must pass his, monocular, scrutiny first. [link] for those unaware of the greatest living Englishman.
eight_nine_tortoise, Mar 10 2009
  

       Cool. Too bad they'd not precess to face Earth all the time, but it would still be cool. Brits would love it, because GMT is the only rational choice of time zone. Everyone else would have to convert.
colorclocks, Mar 10 2009
  

       hold on there. This is going to be an issue. It should be set to eastern standard time, or some easy derivation of it (+12hrs or +/-1hr are acceptable)...   

       Edit: I guess flyingtoaster really ought to choose.
knowtion, Mar 10 2009
  

       Disappointing. I thought this was going to be a version of 'Apollo 13' but one in which the astronauts are rescued from disaster by scantily clad lifeguards. Ah well!
DrBob, Mar 10 2009
  

       they could be cosmic time capsules for the finest terrestrial cheese   

       why not just set cheese wheels in orbit around the moon.Wrapped in aluminum foil naturally. I would bet that it would keep in space and still be delicious in 5000 years.
vfrackis, Mar 10 2009
  

       Cheese is good but the cow would eat it whilst jumping over...unless it was PROCESSED CHEESE!
blissmiss, Mar 10 2009
  

       <strokes chin and says yesyesyes, looking very smart and smug like the rest of you guys. Tries desperately to blend in, fails and tries to hide behind own shame whimpering whywhywhywhywhywhywhy>
zeno, Mar 10 2009
  

       They would need to be at least 200 miles in diameter to become 1/10 that of the moon.   

       Presuming they are made out of cheese (as they should be), that would be 19 quadrillion tons of cheese per ball (@200 mile diameter).
knowtion, Mar 10 2009
  

       So good. +++
placid_turmoil, Mar 11 2009
  

       Takes an eclipse'n and keeps on tick'n.   

       [zeno] Ohhhh nononono no no no you really don't want to fit in. The farther you stay away from this bunch the better. The less sense it makes means you still have some...sense that is. :-)
blissmiss, Mar 11 2009
  

       They might need correctional rockets to allow to for fine tuning and leap-seconds.   

       I wonder how visable they would be when sections of the moon are shaded?
Aristotle, Mar 11 2009
  

       Don't forget the spin correction rockets on the Earths equator, so that the Earths rotation preriod does not get out of time with the clock.
eight_nine_tortoise, Mar 11 2009
  

       I think orbital period is a function of distance (rustles off to look) yes - the orbital period is proportional to the square root of the cube of the distance. Which, by my calculations means that the hour 'hand' would have to be 5.24148 times further out than the minute hand. Quite how far out the minute hand would have to be is beyond my maths at this time, but like the idea, I think it would have to be pretty far out.
zen_tom, Mar 11 2009
  

       The moon has a radius of 1737 km and a mass M of 7.35 x 10^22 kg.   

       The radius of an orbit of period T seconds in a gravitational field where G = 6.67 x 10^-11 is given by:   

       r = (GM(T^2)/2pi) ^1/3   

       edit: should be 4pi^2 :(   

       So I reckon the minute hand would orbit at 400 km above the moon's surface whilst the hour hand would orbit at 9,300 km above.   

       The hour hand would be about three moon diameters away from the moon itself.   

       Employing a polar orbit that straddles the boundary between the face that is always turned to the Earth and the face that is permanently hidden would ensure that the hands would always be visible.   

       It would look fab!   

       Edit - cock up in calculations - see later :(
DenholmRicshaw, Mar 11 2009
  

       Doh, I forgot to factor in the radius of the moon.
zen_tom, Mar 11 2009
  

       this idea is loony.
k_sra, Mar 11 2009
  

       (Nice to see you back here k_sra!) Yes, loony. [DrBob]'s idea is better.
hippo, Mar 11 2009
  

       Those orbit figures look a bit odd - Apollo 8 had an orbit of roughly 180x190km at a shade under 90 minutes. A sixty minute orbit would be lower still.
coprocephalous, Mar 11 2009
  

       + Would the clock appear to be inaccurate the further away from the equator you viewed it from?
Zimmy, Mar 11 2009
  

       Oops, wrong orbit - I'll be back   

       [EDIT] make that highly eliptical at 112x311km, with a period of 128 minutes.
coprocephalous, Mar 11 2009
  

       Could the minute hand actually do this, or would it have to orbit below the surface?
wagster, Mar 11 2009
  

       Dunno, [wags] but they may have to blast a few mountain passes
coprocephalous, Mar 11 2009
  

       [wags] [copro] check-out [Denholm]'s calculations above - they look (after the most cursory of reviews) pretty reasonable to me - and no having to explode anything.
zen_tom, Mar 11 2009
  

       [denholm] I didn't look closely at your calculation. So, I'm just double-checking, that you used the moon's gravity for G.
knowtion, Mar 11 2009
  

       G is the gravitational constant, it doesn't matter what body it belongs to, and there's an M in there that takes care of the moon's mass - so yes, it should be right.
zen_tom, Mar 11 2009
  

       I see. I clearly confused G with g. My bad. \\The radius of an orbit of period T seconds in a gravitational field where G = 6.67 x 10^11 ...\\ 2 things. First, G is 6.67 x 10^-11 (note, it's 10^-11). Second, G always has this value; in ALL gravitational fields (so they say), therefore you could remove "in a gravitational field where" from the definintions.
knowtion, Mar 11 2009
  

       The hour hand would circle roughly 1/3 a diameter away (1,113km above the Moon's surface) and the minute hand... umm...well... let's not dwell on that, rather let's put 12 hour hands up there into their staggered polar orbits and keep every time zone happy; in fact let's make 24 of them so half the world doesn't have to stand on their heads to see what time it is. § x1
FlyingToaster, Mar 11 2009
  

       correct me if i'm wrong, but wouldn't the 'clock' be on the other side of the moon a great deal of the time? [hi, hippo!]
k_sra, Mar 11 2009
  

       //clock be on the other side of the moon ?//
I don't know but the spheres would be subject to Earth's gravitational pull just like the Moon is.
FlyingToaster, Mar 11 2009
  

       Of course this would only work from one hemisphere. When viewed from the other hemisphere the clock would be upside down.
Wrongfellow, Mar 11 2009
  

       So someone would have to fly to the moon twice a year to adjust the balls for daylight savings time?
phundug, Mar 11 2009
  

       Rather than implementing the clock using orbital mechanics, if we made a great big set of train-tracks all the way around the moon, we could sit the dials at the end of long poles that extend from carriages that run along those tracks.   

       If those carriages were powered by means of a coiled lunar spring, it would require regular visits back to the moon in order to wind it back up.   

       The advantage of this implementation method is that with enough tracks and clever engineering, we might be able to set up various mechanisms to support say; perpetual calendar, date window, flyback chronograph, lap timer, dual time display, moonphase indicator and slide rule rotating bezel.
zen_tom, Mar 11 2009
  

       oops - 10^-11 it is   

       But worse (and this is bad news) - my cock up - I forgot to square 2pi - it should be 4pi^2   

       The hour hand would orbit at 1200 km from the centre of the moon. This means the hour hand would orbit below the moon's surface - this is clearly an example of the laws of nature being plain wrong.   

       A two hour orbit would just be above the surface at about 100Km.
DenholmRicshaw, Mar 11 2009
  

       Shirley this ought to be be rightfully named "Moon Clock" since a watch is what one wears on one's wrist?   

       And where do you plan to put the AM/PM indicator?
Canuck, Mar 11 2009
  

       //So someone would have to fly to the moon twice a year to adjust the balls for daylight savings time? — phundug, Mar 11 2009//   

       *goes into shameless fits of giggles for no apparent reason*   

       oh, and [phundug], does have a valid point.
k_sra, Mar 11 2009
  

       [DR] sp. "minute hand", the "hour hand" would be at...6,142km (dropped a zero halfway through a previous calculation)
FlyingToaster, Mar 11 2009
  

       The only thing I can think to do is to capture an asteroid using a spectacular feat of celestial mechanical engineering to place it into the daily orbit around the moon. Then we place a smaller, shiny body to orbit the asteroid once an hour.   

       An asteroid of 10^14kg would support an hour hand at about 300km from it so would be visible from Earth.   

       Not quite a traditional clock face but functional.   

       It's probably not a stable system though so would need lots of maintenance.
DenholmRicshaw, Mar 11 2009
  

       put it in Earth orbit opposing the Moon... but if you're going to do that may as well put a bunch of them in geosynchronous orbits.
FlyingToaster, Mar 11 2009
  

       I think we ought to stick with the tinfoil wrapped cheese. That way, if one accidently strikes the earth, we can maintain a cheese based civilzation until the ash has cleared from the atmosphere.
knowtion, Mar 11 2009
  

       <unable to resist urge to pun>

That's Edam good idea!

<skulks away, head hung in shame>
Canuck, Mar 11 2009
  

       [+] Cleverness/Originality.   

       But ... Since the moon keeps moving around the Earth (or so it seems! Fools...); and since this "satellite" will often be blocked by the moon itself; compounded by the the fact that your "current" longitudinal location on Terra Firma keeps moving - the Earth is spinning (yeah, right: the Earth is FLAT!): probably an 24-hour periodic lunar "polar" orbit gold foil sphere seems to suggests itself... (That ... and/or a "Swiss" cheese satellite.) Cheddar? What were you thinking...
Wily Peyote, Mar 11 2009
  

       \\ where do you plan to put the AM/PM indicator? \\   

       The moon already performs that function.
tatterdemalion, Mar 11 2009
  

       //The moon already performs that function.// Not really [tatterdemalion], in fact, the moon will come up at night only during a completely full moon when its orbit places it on the opposite side of the earth to the sun. For the other 75% of the time, the moon will be positioned in the daytime sky, and is most prominent just prior to and post the full moon phase in the mornings or late afternoons.
zen_tom, Mar 12 2009
  

       //The [minute] hand would orbit at 1200 km from the centre of the moon. This means the [minute] hand would orbit below the moon's surface//   

       Ok, so we blast out an equatorial trench and make it look like the death star. Any objections?
wagster, Mar 12 2009
  

       //blast out trench// One small addition.   

       We'd have to put mirrors at the top of the trench to reflect sunlight onto the hour hand satellite and allow it to be seen.   

       Shouldn't add much to the cost, we could cover it from contingencies.
DenholmRicshaw, Mar 12 2009
  

       The French did try to decimalise time, back during the same revolution that caused the other, more successful, metric systems to emerge.   

       Maybe the solution would be to have a pair of minute hands, that each have a two minute orbit, organised so one is always visible whilst the other is travelling across the dark side?
Aristotle, Mar 12 2009
  

       //Unless time is restandardised to the lunartick, which could include 100 hours per day.//   

       I got lost in imagination from that anno - thinking about what would happen if someone actually did this and put the orbits marking a non-standard time sequence.
Zimmy, Mar 12 2009
  

       Fun fact: Provided the balls are ~200km in diameter, and made from 100nm gold leaf, this would take double the gold ever mined (~300.000 tonnes)
loonquawl, Mar 16 2009
  

       Set the orbital period to Zulu time and never worry about AM/PM indicators. Since Zulu time is based on a 24-hour clock, the orbit could be higher.
Klaatu, Mar 17 2009
  

       How much would a 200 km dia circular disk of aluminium kitchen foil weigh?   

       If that is too much, how about a disk of aluminised mylar?
neelandan, Mar 17 2009
  

       Another reason for war between east and west?
pashute, Aug 07 2011
  

       I clicked to vote yes, and the Yes counter said "42." Is that karma or what?
sqeaketh the wheel, Aug 07 2011
  

       You idiot! Now the Universe will end <link>.
mouseposture, Aug 07 2011
  

       [xaviergisz] <linked idea & anno> wasn't inspiration for this post (that I recall), but yes, kudos to [WcW] and a fresh bun to [nineteenthly].   

       Of course "great minds" and all that. ;)   

       (and umm thanks but really ?)
FlyingToaster, Aug 07 2011
  

       Wouldn't something that big and low experience atmospheric drag? It'll have to be pretty heavy to orbit more than ten thousand years.
Voice, Aug 07 2011
  

       //"Moon Watch" is pretty much my favourite idea on HB...//   

       //(and umm thanks but really ?)//   

       Yep. If I had a few billion dollars lying around, this would be what I would spend it on (after doing all the obvious stuff that one would do with that much money).
xaviergisz, Aug 07 2011
  

       [Voice] I imagine somebody'd have to go up and fiddle with it every few millenia.   

       [x] with a few billion dollars you could give a go at every good idea on the HB and have enough left over to kludge the ones that are good but don't actually work.
FlyingToaster, Aug 07 2011
  
      
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