Half a croissant, on a plate, with a sign in front of it saying '50c'
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astronomer's clock

 clock with adjustable speed
  (+6, -3)
(+6, -3) 		  [vote for,
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A clock to mimick a normal office clock, but with a little wheel in the back that lets astronomy-interested owner adjust the length of a 24-hour day to match the actual speed of some other planet's rotation.
—jutta, Sep 15 1999

Prague Town Hall clock. http://www.discover...e/oldtownhall_v.jpg
A really cool 600 year old clock... [StarChaser, Sep 15 1999]

(??) More information on it. http://otokar.troja.../RelatGrp/Orloj.htm
More in-depth info, including that it was burned down by the Nazis in WW2. [StarChaser, Sep 15 1999]

Martian analemma http://apod.nasa.gov/apod/ap061230.html
From Sagan Memorial Station [lurch, Apr 11 2011]

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       Thanks to the commentators that have helped me progress from medieval to rennaissance models of planetary motion. Obviously, (1) astronomy needs to become a school subject and (2) I shouldn't be involved in setting the curriculum...
—jutta, Dec 21 1999
   

       Reportedly, during the Mars Pathfinder mission, a number of JPL operations techs started sleeping on Mars time so they'd be awake when the (solar-powered) lander was active.   

       Since (as far as I know) this idea hasn't come to pass yet, I presume they used computer programs and Mars/Earth time tables.
—egnor, Mar 05 2000
   

       In a similar vein, there are clocks available that run on what astronomers call sidereal time. This is the time it takes for an object to return to the same apparent position in the sky (off-setting the Earth's movement around the sun)
—mj, Mar 30 2000
   

       In a different artery, has anyone seen the 'astronomical clock' in the city of Prague? I'd love to have a screensaver of that thing that kept time...
—StarChaser, Apr 25 2000
   

       It'd be really cool if it was three dimensional with all sorts of orbit gizmos and such.
—salmon, Dec 15 2000
   

       I knew these guys who decided to go onto a 10 hour day to be more in tune with the metric system. They would sleep from hours 9-1, eat at a certain hour, etc. regardless of when that occured in the real world. Needless to say, they didn't attend too many of their classes, and failed out of school, but hey, it was pretty funny.
—MuddDog, Jun 11 2001
   

       The French tried to do a metric clock after the revolution...it bombed too.
—StarChaser, Jun 12 2001
   

       [salmon]: That's called an "orrery", and they do exist.   

       [MuddDog], [StarChaser]: We have metric calendar ideas in plenty... isn't there a metric time idea floating around here somewhere?
—egnor, Jun 12 2001
   

       2011: More info link from 1999 is dead now.
—pashute, Apr 11 2011
   

       I think if this was for sale on Firebox I'd buy one.   

       I also think that, as with all things from Firebox, its fascination would last for a few [Earth] days. (I collect watches, and love my 24hr watches because they're a bit odd. But, strangely, I never find myself wearing any of them.)   

       (Actually, truth be told, I never wear a watch anyway.)
—MaxwellBuchanan, Apr 11 2011
   

       If you want to make this really geeky, have one clock hand for each planet EXCEPT Earth. To figure out the Earth time, you'd have to really keep track of where we are relative to everyone else.
—phundug, Apr 11 2011
   

       Hang on.   

       There's a problem with this, maybe.   

       Time depends on where you are on the planet, and also on where the equivalent of the Greenwich Meridian is defined.   

       For instance, what time is it on Venus right now?
—MaxwellBuchanan, Apr 11 2011
   

       Venus has a prime meridian as do Mars and Mercury, so there should be no problem setting this watch. With gas giants, it's a little more difficult, but Jupiter apparently has something called Central Meridian Longitude which is a line of longitude defined by a particular time, rather than vice versa. Time still depends on where you are on the planet, but in that respect, this watch is no more problematic than any other.   

       The real problem is what to do about Daylight Saving Time.
—mouseposture, Apr 11 2011
   

       Venus Standard would be the time at the meridian through the central peak of the crater Ariadne.   

       Mars Prime Time would be local at the crater Airy-0.   

       But, yeah, let's go ahead and get started on the Daylight Savings Time thing for Mars - the equation of time over the course of a year runs from about -50 minutes to +40. Some adjusting might be handy.
—lurch, Apr 11 2011
   

       Would you assume you're at the same longitude on Mars as you are on Earth?
—MaxwellBuchanan, Apr 12 2011
   

       [MB] Well, I see what you mean, but that's precisely as much, or as little of an issue with a Venus clock as with a conventional Earth clock. The worst you can say is that the Venus clock is unlikely to be useful, since you're unlikely to be on Venus.   

       But clocks* are commonly set to a location different from the one where they're located. The proposal would be a splendid addition to the display in an airport or train station, with half a dozen clocks showing time in different cities. Alongside "GMT," "New York," "London", "Moscow," "Tokyo," would be "Venus (Ariadne Crater)" or "Mars (MPT)" You can't say that wouldn't be cool.   

       *The proposal's for a clock, not a watch, contra my error above. But even watches are sometimes set to elsewhere- time.
—mouseposture, Apr 12 2011
   

       //Would you assume you're at...// some point of interest, I presume.   

       I would, personally, set my clock to AMT-04:45 (AMT=Airy Mean Time) to correspond to the location of my selected homestead in Kasei Vallis. It's a real geek-deflating moment to have somebody ask what your time-mark points to, and have to answer "dunno". (The Opportunity rover is only about -22 minutes local solar from AMT(although the team uses -1:01:06; they offset for the equation-of-time at a point halfway through the (90 day!) mission(bwahahaha!)))
—lurch, Apr 12 2011
   


 

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