radio time code clock error

Possibly by consensus. Just make reference measurements on as many inaccurate sources as possible, average them together, and by the magic of statistics, the average will be more accurate than any individual measurement. That's because given a sufficiently large supply of erroneous data, the errors tend to be in opposite directions and cancel each other. For example, you could average the noon sight reading from a huge number of sundials or sextants, and the average will give you NIST grade accuracy.

If this is a problem for you, just buy one of these: and you won't have to worry about the sundials and sextants that the NIST probably secretly uses for calibration. You'll have a personal time standard that you can trust. Or, just build your own: Once you have an accurate clock, all you need to do is decide which time standard you want to use (LT, GPS, UTC, GMT, GMAT, GAST, SAT, TAI, Loran, MST, UT, TDT, TBT, TGC/TBC, etc. This might help you decide how to set your cesium wrist watch: Note that some of these are NOT astronomically based, do not include leap seconds, were established for political reasons, and don't agree with other standards. For example, the current differences between UTC, GPS, and TAI at: Also, please note that all of these standards were created and are managed by various committees, and we all know how ineffective a committee can be at getting things right.

Perhaps you should just get a wrist sundial: One can't trust the time gods to get it right:

They don't call it "Coordinated Universal Time" (UTC) for nothing.

My wife is a manager at Australia's National Measurement Institute, and works directly with the local "Time Lord" who's ultimately responsible for one of the six atomic clocks that are used to determine UTC. He's a nice bloke, too.

Of course, nothing in this would allow us to detect a systematic slow-down in time itself, but if the effect was undetectable, how would it matter? As long as everything slowed down at the same rate, it would cause no effect that we could measure. So we compare the six clocks as they wander around each other, and we try to pick a mean line between them and call that line "coordinated time". And of course we do research to try to find a way to build a clock which tracks that mean line better than current ones do, which is how we got to where we are.

Clifford Heath.

It's a specific case of a very general problem, namely how to estimate and control systematic errors in a measurement. Generally speaking, if your hydrogen maser and your neighbour's caesium clock and your Russian brother-in-law's Bose-Einstein condensation agree, you can be pretty confident. Otherwise it's a real headache.

Cheers

Phil Hobbs

Clifford Heath: The biggest variant here is the planet itself. Earth is slowing down, overall, at a more rapid rate than any of the world's atomic clocks are speeding up or slowing down. It's why an "ephemeris" second is inserted every so many years.

No, the planet is not changing the rate at which time passes, and it's not affecting our ability to measure time.

Yes, but that has nothing to do with how we improve our ability to measure time. Remember I was responding to N_Cook's comment:

"The new generation of atomic clocks, accurate to 1 second in 15 billion years,supposedly - how do they know , without a more accurate clock than that to check it against?"

The earth's slowing is also somewhat chaotic, inasmuch as equatorial weather affects the sea-level heights, which introduces noise into the earth's angular moment of inertia, and hence its rate of rotation. That has nothing however to do with how we know we're measuring time accurately.

Awesome. Are there any Youtube videos of spacecraft in otter space? I do love otters, they're my favourite creatures.

;)

And yet if you were aiming at Pluto via a slingshot around Venus, you don't want to be 17km off on approach to Venus. I can't do the math, but I suspect it's rather closer to 17cm.

I've only seen sea otters once, on a visit to Monterey. I guess you also are more fond of animals you don't have locally.

The common otter is super cute. One day, I want to learn how to ot. it looks like fun.

It might help to mention that we have two types of time accuracy. One is sidereal time, where 12AM on Jan 1 is astronomically correct and is used to aim telescopes on earth. This is where we says "at the tone, the time will be... (beep). The other is the length of 1 second, minute, hour, day... year which is a numerical count of how many wavelengths of light or cycles of atomic gigahertz vibrations pass during these intervals also known as atomic time.

The problem is that the two systems don't quite coincide. The current difference between UTC and International Atomic Time (UTC-TAI) is now

The fun starts when tracking spacecraft in otter space. Not only does one have to deal with relativistic effects, but one also has to use a time system that is independent of how the earth spins, wobbles, and thrashes around. It would be a major disaster if a leap second were thrown into the timing if you're tracking a spacecraft such as Voyager

There's quite a bit of detail summarized here including what would happen if GPS (atomic) time were "harmonized" with local time. Only the top part is up to date but the old stuff is interesting.

Nope. Sidereal time is different from civil (solar) time. The Earth rotates 365 and change times per year with respect to the Sun, but 366 and (the same) change with respect to the fixed stars. So the two get out of phase pretty fast.

Well, worse if you don't think that the Gregorian reform was an advance. Pretty soon the vernal equinox would have been in February. Personally I think that civil time is more important than atomic time. Folks who need to know the difference, do.

If we knuckle under to atomic time in civil life, our version of the Julian problem is that midnight by the clock will soon start occurring at sundown. The leap second inconvenience principally affects software developers (and those who trust them). ;)

You'd be off by 17 km. Is Voyager 1's position known to that accuracy? Didn't think so.

Cheers

Phil Hobbs

Whoosh! You completely missed the point.

The reason we know it's getting longer is because we have clocks that *aren't* slowing down. I was talking entirely about *how we know* they aren't slowing down.

No,they don't. They just count the time passing, and we decide what numbers to assign to the days, hours, minutes, seconds. The *numbers* are not the *time*.

And that is *exactly* what is happening. That is why we need leap seconds etc, to adjust the *numbering* to match the planet's motion. But adjusting the numbering doesn't make time pass slower or faster.

Sorry, my mistake.

The Julian calendar was working just fine for 1500 years as everyone know how to tweak the date so that it matches the solar calendar. That was fine for farmers and bankers, but didn't do much for the church, which had the bad taste to celebrate their holidays by the calendar month and date. Most everyone else used the signs of the zodiac to set the beginning of the month. That worked well for the GUM (great unwashed masses) except that the church equated the zodiac with pagan religions, alchemy and witchcraft, so that wasn't going to work. A pope previous to Gregory XIII tried to switch the holidays to the zodiac months (can't find the name) but gave up before going public. I suspect that Gregory XIII must have had second throughts when he allowed the astronomers to fix the calendar. At least they named it after him, so I guess he was happy.

Incidentally, if you want a really screwed up calendar, try the Hebrew calendar, which adds an extra month every 2 or 3 years, every 7 of 11 years. There's nothing like a duplicated month (adar) to create confusion.

I don't see a problem. If every political time standards organization can have it's own time standard, I see no reason why they can't expand theirs to a calendar standard. You just pick the calendar that is appropriate for whatever you're doing. It's not much different than the US before the railroads, where every town had it's own time and DST standard.

Yeah, there were some hiccups in 2012. I missed the fire drill, but still managed to get wakened by a customer wanting to know why their backup failed. Stupid me had set cron to start the backup exactly at midnight. That worked, but one second later, it started a 2nd backup during the leap second. Why, I don't know, but that's what the log files showed. I killed both processes and started over.

I was thinking of it in terms of the change in angular error for the rotation of the earth. degrees = 17km/40,075km * 360 degrees = 0.15 degrees Let's see if that works. Voyager 1 and 2 uses the DSN (deep space network) with 34 or 70 meter dishes at about 8 GHz. That's about 67dB gain and a -3db beamwidth of about 0.07 degrees for the 34 meter dish, and 73 db gain and 0.04 degree beamwidth for the 70 meter dish. Since the DSN tracks the rotation of the earth, a change of 0.15 degrees would move the main lobe sufficiently to miss the spacecraft.

Yep:

Photos of some otter space otters:

I don't really like otters. Years ago, I was diving off Monastary Beach in Carmel, CA. There was an otter floating on the surface sleeping. My dive partner decided to poke the otter with a pole. It looked down at us, and went back to sleep. However, my partner kept poking the otter until it became irritated. It dived down under us, came up, and bit me in the buttocks though my wet suit. It wasn't much of a bite, but did manage to ruin my day.

These days, I look at them with otter contempt.

IIRC the Etruscan day started at midday, the Jewish day at 6am, the midnight start is just a hangover from the Romans, so sundown start is no great problem

Clifford Heath wrote: "No, the planet is not changing the rate at which time passes, and it's not affecting our ability to measure time. "

HOW can you make such a statement??? If the planet is gradually slowing down, over millions of years as reported, the period of time from noon to noon(or midnight to midnight), is getting LONGER. Our hyper-accurate master clocks have to account for that somehow.

"Yes, but that has nothing to do with how we improve our ability to measure time. Remember I was responding to N_Cook's comment:

"The new generation of atomic clocks, accurate to 1 second in 15 billion years,supposedly - how do they know , without a more accurate clock than that to check it against?" "

"The earth's slowing is also somewhat chaotic, inasmuch as equatorial weather affects the sea-level heights, which introduces noise into the earth's angular moment of inertia, and hence its rate of rotation. That has nothing however to do with how we know we're measuring time accurately. "

OF COURSE IT DOES!! If our super-accurate clocks don't account for an inconsistent Earth, then sunrises, sunsets, and everything else will start happening later & later by those clocks. Sunrise in June in Connecticut will come at

That's because of PLANET drift, not clock drift. And overall, it is slowing down, not speeding up.

The Earth is a natural, living object. It's impossible to match its movement with precision, repetitive movements.

I never said it did. If we as a species never had clocks at all, I'd guess we all just get used to this light & dark cycle called days getting longer and longer all the time and not even think twice about it.

The innate human biological clock is nearer 25 hour-day than 24 hours, from the sensory deprivation experiments conducted in caves. Everyone else, in normally life, gets sync'd to this artificial 24 hour system.

I suppose 24 developed out of need for dividing the day evenly. Of course, that doesn't explain the 7-day week. LOL

The French Revolution also metricated the clock (10 hours in a day, 100 min utes in an hour, 100 seconds in a minture) and the calendar (3 decades in a month, 10 days in a decade, plus complementary days. This appears to be o ne part of the metric system that was not widely adopted.