An Update on Leap Seconds (2022)
dotat.at
dotat.at
Ideally, one would have a monotonically increasing time from some event, but then transforming that into some human readable time is complicated. And of course, what actually is the human readable time? When should 'noon' actually be and should it be adjusted continuously with leap seconds, minutes, etc.?
On the other hand, we already have leap seconds. They're not much of a problem.
Well, leap seconds are going away, so we don't.
They were never adequate for the long-term anyway, as the "two leap seconds a year" scheme will break down as the earth's rotation slows over the centuries and more and more leap seconds will be needed.
We're talking about an hour time drift over a few thousand years. Does that really matter? It's like caring what Julius Caesar's sense of "morning" or "evening" was. They never really solved any practical problem.
Approximations in calendar time can be used for the future where precision timekeeping is not needed (the holiday party next year at 8:00PM), and exact monotonic timestamps can be used where precision is needed (e.g. the timestamp to start a re-entry or orbital insertion burn around Mars).
Our calendars are already merely tags/counters for physical events (solstices, new moons, high noon) we observe, so making that distinction official in timekeeping standards makes sense to me.
Time seems to simply be a way to keep track of matter in space, that is it seems to be a construct to explain the state of matter. Unless matter's state is being undone in space, I can't imagine how time would move backwards.
So lets call the new timescale NTS. Lots of records and timestamps have been made using UTC. So now we'll need a way of converting timestamps between UTC and NTS. We already have future timestamps in UTC; e.g. "This record must be destroyed at midnight UTC, Jan 1 2036". So even after we've switched to NTS, we'll still need to calculate UTC, so we'll still need leap-second announcements.
Timescales are a deep mess, and as the author notes, having them managed by a bunch of treaty organizations is nuts; treaty organizations are inherently political (and they move like molasses in winter).
If they just stopped adding leap seconds to UTC at some point, why would there be any ambiguity about the definition of any given UTC time?
> So lets call the new timescale NTS. Lots of records and timestamps have been made using UTC. So now we'll need a way of converting timestamps between UTC and NTS. We already have future timestamps in UTC; e.g. "This record must be destroyed at midnight UTC, Jan 1 2036". So even after we've switched to NTS, we'll still need to calculate UTC, so we'll still need leap-second announcements.
The schedule of leap seconds in the future isn't known, so such a timestamp isn't precisely defined yet anyway. Abolishing the practice fixes this.
That seems a fair point; and rather obvious - I'm embarrassed thatI don't have an answer.
Adjust for local display at the time you display it and only at the time you display it.
We could all agree to stop adding leap-seconds, and nothing would change in 99%+ of all UTC time-handling code. We just wouldn't get any more leap seconds. The process of adding them is manual anyways, so we could stop it without breaking anything.
Well, until some sufficiently influential government or organization gets annoyed with the discrepancy with solar time and comes up with their own correction to the local clocks under their jurisdiction. Then at the bare minimum you need all the commonly used date/time libraries to be updatable with this information. Existing solutions like the tz database [0] might already technically support this, although I have to imagine that the logistics will be annoying at best.
Leap seconds are a poor band-aid "solution" to a problem that nobody has.
In all practical senses I don't think it would matter much if this record is destroyed a few seconds early or late in such a case...
Or the amount of rotation required to point towards the sun again, which is slightly more than one rotation (remember, we orbiting while spinning, so noon to noon is a bit more than 360°). This is a solar day; your definition is called a "sidereal day" (and is a real thing, too).
(And the solar definition has issues, too, which leads to, e.g., mean solar time…)
What I do not understand, considering the above (Julian years and days have been used for a long time in respectively paleontology and astronomy, haven't they ?) as well as from TFA :
> Abolishing leap seconds will be helpful for users that have very tight accuracy requirements. UTC is the only timescale that is provided by national laboratories in metrologically traceable manner, i.e. in a way that provides real-time access, and allows users to demonstrate exactly how accurate their timekeeping is.
> TAI is not directly traceable in the same way: it is only a “paper” clock, published monthly in arrears in Circular T as a table of corrections to the various national timescales. (See the explanatory supplement for more details).
So, what are we waiting for to just have both scientific time and civil time being broadcast separately (and scientific time with more precision and frequency, not less !), and then you use one or the other as appropriate ?
That would require either doubling the radio frequencies (and other channels) used for time broadcast, or changing the transmission format to include both (so not really separate). Some systems actually broadcast the current leap second count along with UTC, so TAI can easily be derived. Of course, that presumes that UTC and TAI keep being related by a leap second count. Going to fractional seconds of delta would again require changing protocols and data formats.
In addition, we’d presumably still like a civil-time second to be the same as an SI second, and not go back to the “rubber seconds” of the 1960s. But how then would we handle the fact that the solar day isn’t exactly 86400 SI seconds [0]? Add/remove some fractional seconds at the end of each civil day? That might cause even more issues in software than leap seconds.
Right, leap seconds it is then, but note that that and minutes/hours/days/years here is something that is only required for human interfaces, while the computer itself only cares about a monotonically increasing seconds counter on its internal clock, which is required to be stopped/started/re-adjusted once in a while anyway.
Oh, and conversion between scientific and civil time is then the job of local polities, which they do for timezones anyway.
The current answer is everyone uses UTC, and they keep synchronized by observing the one universally disseminated time, which is UTC.
You use and synchronize to the same time standard as the world-metrologists do (TAI), the whole issue is that that's not the one that is being disseminated as the article and I already pointed out.
UTC is a (strange) compromise between both: ticking SI seconds like TAI but being kept within 1 second of UT1.
Timezone bands are massive. If they were perfectly straight (they aren't) then civil time in any one place would be off by up to 30 minutes in either direction, depending on the location. In reality they line up with political entities instead, creating even larger discrepancies (with the extreme case being China, where some regions are hours off).
Compared to that, a second every couple of years is completely irrelevant.
1 sidereal day is about 4 minutes shorter and the time it takes for the stars to be in the same position.
As far as I know, unless you're doing certain types of astronomy, you're using solar days.
There is lot to unpack in this statement.
1) In around 1970 the importance of celestial navigation is questionable. Systems like LORAN and Decca were well established, and OMEGA became operational in 1971.
2) The importance of second-level accurate celestial navigation is even more dubious, considering that celestial navigation is not super precise to begin with.
3) Most crucially the link between the needs of navies and civil time is weak; even if we assume that navy needed accurate approximation of UT, it doesn't explain why civil time needed to follow.
Note that afaik celestial navigation relies on nautical almanacs that are published yearly. It would have been trivial to include DUT1 correction values in there too if needed.
I can count on zero hands the number of times I've been on a sailboat where everything worked perfectly. This is a function of cost moreso than criticality, but the amount of time and energy required to upkeep a sailing appliance that consistently endures some of the worst things nature can throw at it would practically require replacing every part with every sail.
Sailboats shake, vibrate, and shudder as they are subjected to wind and waves. Topside parts enjoy the added joy of being continuously subjected to sun, salt, and wind.
In short, things break. Slightly longer, it is fair to expect that on any given day, something will be broken. Whether a car that holds a mainsail to its mast, or a fuse that powers your navigation equipment, or what have you, those systems are great and wonderful so long as they are operational, but if you are halfway across the Atlantic ocean, hundreds of miles away from the nearest land mass in the dark, there is no Radio Shack to visit, and no way to find it without having to fall back to a compass and some celestial orientation.
No matter how good they are advertised as being, absolutely zero systems should be considered trustworthy in a big sea.
There is no Radio Shack for marine electronics, but it'd be great if there were.
And my understanding is that if celestial navigation isn't good enough you are probably close enough to land to just navigate based on sight and map.
Let's say you do something reasonable, like put an atomic clock on the moon, or anywhere really, but let's stick with the moon.
You build your clock, you sync it with the Naval Observatory., and launch it to the moon.
48 years later, who shows up? That's right, the leap second.
Your lunar clock is losing 56 microseconds a day due to an insufficiently curvy spacetime (e.g. gravity).
So unless you differ from Earth's calibration on purpose, you won't lose 56 microseconds a day. You'll stay in sync.