Timeline for answer to Why are leap seconds needed so often? by Peter Cordes
Current License: CC BY-SA 4.0
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19 events
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| Jan 29, 2023 at 21:23 | comment | added | PM 2Ring | Steve Allen has some great info in physics.stackexchange.com/a/402062/123208 & ucolick.org/~sla/leapsecs | |
| Jan 29, 2023 at 21:14 | history | edited | PM 2Ring | CC BY-SA 4.0 |
Corrected info about the defining epoch for the SI second.
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| Jan 29, 2023 at 20:29 | comment | added | Peter Cordes | @PM2Ring: It's been a while since I looked at this answer or thought about any of the stuff it involves. If there's something that could be improved (a wrong detail or just adding a footnote with that info an wiki link), please edit if you have the time. (And I guess comment to let me know so I can take a look and see if I want to reword anything.) | |
| Apr 24, 2018 at 18:03 | comment | added | Peter Cordes | @DavidHammen: Thanks, I hadn't realized the year-to-year variation dominated the average trend over the short term. Updated my answer to say that, and added a link to yours. | |
| Apr 24, 2018 at 18:00 | history | edited | Peter Cordes | CC BY-SA 3.0 |
It's not near-constant at all in practice. But keep that phrasing as simple as possible and add the practical details as a footnote.
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| Apr 24, 2018 at 10:49 | comment | added | David Hammen | Re leap seconds accumulate at a near-constant rate: That's not the case at all. Nine leap seconds were added in the first eight years after implementing the concept of leap seconds while only two were added over the 13 year span starting in 1999. The rate is anything but uniform. | |
| Apr 24, 2018 at 8:32 | comment | added | Peter Cordes |
@Gizmo: ms/day is a measure of the current error-accumulation rate. But it's not constant because the Earth's rotation is slowing down, so we also need a measure of the acceleration in that error-accumulation velocity. Next century will need more leap seconds than this century. (Updated my answer to show where ms / day comes in, since I didn't use that exact phrase in the paragraph about it). So yes, we need ms/day, but it's an also not an instead.
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| Apr 24, 2018 at 8:29 | history | edited | Peter Cordes | CC BY-SA 3.0 |
added 57 characters in body
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| Apr 24, 2018 at 8:05 | comment | added | Gizmo | so, why is the unit "milliseconds per day per century" ? why couldn't they just use "milliseconds per day"? Because as we keep adding leap seconds there are less days? Meaning the unit ensures that you add a constant amount of milliseconds in a century, like 73 seconds per century? Why not such a measurement? | |
| Apr 23, 2018 at 6:37 | comment | added | Peter Cordes | @ShadSterling: Updated with numbers because there's some interesting stuff to say. It was clear enough before, IMO: once you know that deceleration and current spin rate were independent, the confusion is resolved and you can obviously infer the current mismatch from the rate of leap second insertion. | |
| Apr 23, 2018 at 6:34 | history | edited | Peter Cordes | CC BY-SA 3.0 |
Add the hard numbers and a link to the USNO's excellent article
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| Apr 23, 2018 at 0:05 | comment | added | ShadSterling | @DawoodibnKareem part of the OP's misunderstanding seemed to be in thinking that leap seconds correct for changes in the length of a solar day due to the changing rate of rotation, prompting the question of why leap seconds appear to happen far more often than would seem necessary for that rate. OP is right about the rate of slowing, but wrong about how that relates to leap seconds. As this answer says, leap seconds correct for a different error, but this answer didn't mention the much higher rate of that error, without which it doesn't fully explain why leap seconds happen so much more often. | |
| Apr 22, 2018 at 19:27 | comment | added | Dawood ibn Kareem | @Jasper No, not a misunderstanding. OP said that the slowing down is of the order of milliseconds per century. My understanding is that this is correct - we'd need far more leap seconds if the earth slowed down by milliseconds per day each day, rather than each century. | |
| Apr 22, 2018 at 19:25 | comment | added | Dawood ibn Kareem | @ShadSterling Yes, the error is in the order of milliseconds per day, but the actual slowing down (that is, the rate of change of error) is much, much less than that per day. So OP is correct. | |
| Apr 22, 2018 at 16:20 | comment | added | JEB | Although the phrase "near-constant rate" is subjective--I would say there is a linear component arising from the difference in day length now and when the day was defined (1900) and a strongly irregular component (mostly from moment of inertia variations) that precludes the prediction of leap seconds beyond 6 months time. | |
| Apr 22, 2018 at 11:09 | comment | added | Peter Cordes | @Jasper: yeah, I thought the other answers were all failing to address the real misunderstanding, that's why I posted this :P | |
| Apr 22, 2018 at 11:07 | comment | added | Jasper | This is the answer that addresses OP's misunderstanding of "milliseconds in a century". | |
| Apr 22, 2018 at 3:51 | comment | added | ShadSterling | It's worth noting that the error here is one or two milliseconds per DAY, not per century, so it takes less than 1000 days to be off by a second. | |
| Apr 22, 2018 at 1:39 | history | answered | Peter Cordes | CC BY-SA 3.0 |