Is it negative leap second time?  - Page 1
Forum section: electronics / general

author: cdev
author_rank: Super Contributor
timestamp: January 22, 2021, 09:51:02 pm
content: Whooooo...I'm sure that I have not been the only person wondering why we had not had a leap second in a while.https://www.space.com/earth-spinning-faster-negative-leap-second.html"Even time did not escape 2020 unscathed.The 28 fastest days on record (since 1960) all occurred in 2020, with Earth completing its revolutions around its axis milliseconds quicker than average. That's not particularly alarming — the planet's rotation varies slightly all the time, driven by variations in atmospheric pressure, winds, ocean currents and the movement of the core. But it is inconvenient for international timekeepers, who use ultra-accurate atomic clocks to meter out the Coordinated Universal Time (UTC) by which everyone sets their clocks. When astronomical time, set by the time it takes the Earth to make one full rotation, deviates from UTC by more than 0.4 seconds, UTC gets an adjustment.Until now, these adjustments have consisted of adding a "leap second" to the year at the end of June or December, bringing astronomical time and atomic time back in line. These leap seconds were tacked on because the overall trend of Earth's rotation has been slowing since accurate satellite measurement began in the late 1960s and early 1970s. Since 1972, scientists have added leap seconds about every year-and-a-half, on average, according to the National Institute of Standards and Technology (NIST). The last addition came in 2016, when on New Year's Eve at 23 hours, 59 minutes and 59 seconds, an extra "leap second" was added. "

author: nfmax
author_rank: Super Contributor
timestamp: January 22, 2021, 10:01:37 pm
content: surely, the opposite of a leap second is a look second?

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: January 22, 2021, 10:41:16 pm
content: Looking at the graph, it does not seem likely we'll need to inject a "negative leap" second before the Earth resumes its long-term pattern of deceleration.Good example ofBetteridge's law of headlinesthough.

author: magic
author_rank: Super Contributor
timestamp: January 23, 2021, 09:41:29 am
content: Quote from: I wanted a rude username on January 22, 2021, 10:41:16 pmQuoteTruth confirmed

author: rs20
author_rank: Super Contributor
timestamp: January 23, 2021, 09:47:52 am
content: Dang it. I've been hoping to hold a leap second party at my work; looks like it'll be a long wait...

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: January 23, 2021, 10:36:59 pm
content: During long "dry spells" like this and the one prior to New Year's Eve 2005, developers tend to forget about leap seconds and stop testing against them. So when the next one comes ... it's going to be more entertaining than average.

author: Cerebus
author_rank: Super Contributor
timestamp: January 24, 2021, 12:59:08 am
content: Quote from: rs20 on January 23, 2021, 09:47:52 amBy the time a leap second comes around I've usually something time-nutty that I'm waiting to give a real live test. Sure, I've already tested everything with unit tests and faked inputs, but there's no substitute for sitting there watching the time click around to 23:59:60 and berating the world for starting to cheer 1 second early.I too will probably be waiting a long time to have that satisfaction again.Although it doesn't look too likely to actually happen, a negative leap second would certainly give a lot of systems real world tests as 23:59:58->00:00:00. I suspect a lot of borkage in the wake of that.

author: cdev
author_rank: Super Contributor
timestamp: January 24, 2021, 01:27:57 am
content: I had certainly never considered this happening.The idea of losing and then gaining angular momentum within the context of conservation of energy is mysterious, although I suppose a good example where this effect can be seen is in classical ballet where dancers routinely manipulate this effect during a "fouette" ?"Due to conservation of angular momentum, a dancer's rotational inertia affects thespeed at which he or she rotates. During a pirouette, a dancer maintains the same position,with her bent leg and arms very close to the body, allowing a fairly rapid spin. However,during a fouette, a dancer whips her leg out to the front and extends her arms, increasingher rotational inertia and thus decreasing her rotational speed. As the dancer pulls herarms and legs back in, she speeds up at the end of a fouette' rotation.In general, a straighter body also decreases the dancer's rotational inertia, allowing herto turn at a faster rate. Thus, proper posture of not only the dancer's arms, but also herupper body and leg are important. Maintaining a straight leg and avoiding knee bendallows the dancer to maintain proper posture, contributing to better balance and greaterturn speed. Understanding proper turn alignment allows dancers to properly exploit theangular momentum of their bodies, and appear more graceful during turns."----I wonder, have we ever even had a negative leap second before?

author: rs20
author_rank: Super Contributor
timestamp: January 24, 2021, 01:46:26 am
content: It's not "gaining and losing angular momentum". Earth is steadily losing angular momentum (transferring it to the moon), but the angular velocity goes up and down as the rotational inertia changes (tectonic movements, etc c.f. ice skater moving their arms in and out, as you pointed out.)(Btw, conflating conservation of momentum and conservation of energy is a common mistake, try to avoid it.)

author: cdev
author_rank: Super Contributor
timestamp: January 24, 2021, 02:24:28 am
content: If we're transferring it to the Moon we're not losing it, IMHO!Since we're literally joined at the hip, as shown by the fact that only one side of moon always faces the Earth (also likely due to the varying mass internally of the moon, a similar phenomenon to the use of a mast on a space vehicle to stabilize its rotation. )I should have made it clearer that I was quoting somebody. (Pirouette and Fouette Comparative Analysis: Results and Discussionhttps://dspace.mit.edu/bitstream/handle/1721.1/98953/921147498-MIT.pdf)I went looking for a description of that phenomenon which I thought was just called a "Pirouette" but it turns out that the thing I was thinking about, is actually a "fouette" and it is likely also whats is causing the speedup as more dense portions of the Earths interior contents shifts its weight..Quote from: rs20 on January 24, 2021, 01:46:26 am

author: Cerebus
author_rank: Super Contributor
timestamp: January 24, 2021, 11:39:49 am
content: Quote from: cdev on January 24, 2021, 02:24:28 amThat's a bit like saying you're not losing money if it's being transferred into your wife's shoe and handbag collection!

author: KK6IL
author_rank: Regular Contributor
timestamp: January 25, 2021, 02:39:37 am
content: QuoteIf you think it is lost, ask her for a second opinion.

author: tkamiya
author_rank: Super Contributor
timestamp: January 25, 2021, 04:50:05 am
content: I'm not spending my money on yet another test equipment. I'm just reclassifying my money.

author: Cerebus
author_rank: Super Contributor
timestamp: January 25, 2021, 05:33:05 pm
content: Quote from: KK6IL on January 25, 2021, 02:39:37 amWhen SWMBO wants me to have afirstopinion she'll tell me what it is*.*Not really.