Midnight Comes a Fraction Sooner as Earth Spins Faster (theguardian.com) 43
If time feels tighter than ever of late, blame it on the revolution. On 29 June this year, Earth racked up an unusual record: its shortest day since the 1960s, when scientists began measuring the planet's rotation with high-precision atomic clocks. From a report: Broadly speaking, Earth completes one full turn on its axis every 24 hours. That single spin marks out a day and drives the cycle of sunrise and sunset that has shaped patterns of life for billions of years. But the curtains fell early on 29 June, with midnight arriving 1.59 milliseconds sooner than expected. The past few years have seen a flurry of records fall, with shorter days being notched up ever more frequently. In 2020, the Earth turned out 28 of the shortest days in the past 50 years, with the shortest of those, on 19 July, shaving 1.47 milliseconds off the 86,400 seconds that make up 24 hours. The 29 June record came close to being broken again last month, when 26 July came in 1.5 milliseconds short.
So is the world speeding up? Over the longer term -- the geological timescales that compress the rise and fall of the dinosaurs into the blink of an eye -- the Earth is actually spinning more slowly than it used to. Wind the clock back 1.4bn years and a day would pass in less than 19 hours. On average, then, Earth days are getting longer rather than shorter, by about one 74,000th of a second each year. The moon is mostly to blame for the effect: the gravitational tug slightly distorts the planet, producing tidal friction that steadily slows the Earth's rotation. To keep clocks in line with the planet's spin, the International Telecommunication Union, a United Nations body, has taken to adding occasional leap seconds in June or December -- most recently in 2016 -- effectively stopping the clocks for a second so that the Earth can catch up. The first leap second was added in 1972. The next opportunity is in December 2022, although with Earth spinning so fast of late, it is unlikely to be needed.
So is the world speeding up? Over the longer term -- the geological timescales that compress the rise and fall of the dinosaurs into the blink of an eye -- the Earth is actually spinning more slowly than it used to. Wind the clock back 1.4bn years and a day would pass in less than 19 hours. On average, then, Earth days are getting longer rather than shorter, by about one 74,000th of a second each year. The moon is mostly to blame for the effect: the gravitational tug slightly distorts the planet, producing tidal friction that steadily slows the Earth's rotation. To keep clocks in line with the planet's spin, the International Telecommunication Union, a United Nations body, has taken to adding occasional leap seconds in June or December -- most recently in 2016 -- effectively stopping the clocks for a second so that the Earth can catch up. The first leap second was added in 1972. The next opportunity is in December 2022, although with Earth spinning so fast of late, it is unlikely to be needed.
IERS... (Score:1)
Re:IERS... (Score:4, Informative)
They have a long way to go since they think this:
Broadly speaking, Earth completes one full turn on its axis every 24 hours. That single spin marks out a day and drives the cycle of sunrise and sunset that has shaped patterns of life for billions of years. But the curtains fell early on 29 June, with midnight arriving 1.59 milliseconds sooner than expected.
This is utterly false!
Time is not simply "tied to the rotation of the earth". One day is 24 hours and 1 rotation of the earth is ~23h56m.
If either the rotation of the earth OR its orbit period around the sun vary slightly, we need to adjust our clocks if we want to keep in sync.
Earth rotation period is almost exactly 23 hours and 56 minutes, ~23h56m04s. Yet, we have a 24 hours day due to the orbital period around the Sun.
Here are some numbers with bc. Background: if the Earth was tidally locked like the moon, it would still rotate on itself once every orbit so we need to take into account 1 rotation every orbit. (For the moon, orbit period == rotation on itself period, ~28 days):
23*3600+56*60+4
86164
(86400-(86164/365.25))/3600
23.9344710624 # 23 hours
0.9344710624*60
56.0682637440 # 56 min
0.0682637440*60
4.0958246400 # 4 sec
In short, the daily noon alignment with the Sun arrives later because the Earth is also moving around the sun so the Earth needs to make a little more than one rotation to align with the Sun again from day to day.
Re: (Score:2)
Also, as maxwell demon wrote:
Note also that the day (as in time between two consecutive midnights) is not constant length because of the slightly elliptic orbit of the Earth. During Northern hemisphere's summer Earth is farther away from the sun than during Norther's hemisphere's winter, therefore it is moving more slowly along its orbit.
Also, the speed of rotation relative to the stars isn't completely constant either because the mass distribution of Earth changes due to geological processes.
... and then add one day (Score:2)
Re: (Score:2)
Which - according https://medium.com/the-philipe... [medium.com] - means that the Earth has to rotate about 361 degrees for the same spot to be in the same relative position, which gives you a time much closer to the 24 hours. It also means that the definition of a "day" depends on who is using it and what for, which means we've got oodles of different sorts of day. And, indeed, oodles of different sorts of year.
Re: (Score:2)
A full rotation is 23 hours, 56 mins, 4.1 seconds, IIRC, with a complete orbit being being 365 days, 6 hours, 9 minutes, 9 seconds.
However, because the Earth rotates around the sun, yada yada yada, the Earth has to rotate an extra degree for the same spot to be in the same position relative to the sun, etc. https://medium.com/the-philipe... [medium.com]
So a day is closer to 24 hours than the rotation suggests, so we don't have to add leap minutes every day. Still, it means that we've got multiple definitions of "day" an
It makes sense. (Score:5, Funny)
It's global warming.
Re:It makes sense. (Score:4, Funny)
Re: (Score:2)
Between global warming and the shorter days I think it's clear the earth is done with this shit and wants it over sooner.
Re: (Score:2)
It's global warming.
Nope. Global warming slows the earth's rotation.
As mountain glaciers melt, they flow to the sea, reducing the earth's moment of inertia and causing it to spin faster.
But this is overwhelmed by ice melting near the poles and spreading over the ocean. The thermal expansion of the oceans and atmosphere also slows the spin.
Re: (Score:2)
It's global warming.
Nope. Global warming slows the earth's rotation.
As mountain glaciers melt, they flow to the sea, reducing the earth's moment of inertia and causing it to spin faster.
But this is overwhelmed by ice melting near the poles and spreading over the ocean. The thermal expansion of the oceans and atmosphere also slows the spin.
Well, yes. The article actually does discuss (with supporting links) the possible causes of changes in the Earth's rotational speed:
.
Re: (Score:3)
It's global speeding.
Re: (Score:2)
Moon and speed of rotation (Score:3)
The Moon is moving away from Earth at about an inch and a half each year. Since its effect on our rotation lessens as it moves away, will at some point the Moon be far enough away that the Earth's rotation might speed up (slightly)?
Re: Moon and speed of rotation (Score:2)
I don't think so.
I think the impact takes energy out of the spin, so the energy is gone.
Re: (Score:2)
The Moon is moving away from Earth at about an inch and a half each year.
Was it something I said?
Re: (Score:1)
The Moon is moving away from Earth at about an inch and a half each year.
Was it something I said?
Fed up with our bullshit, the moon just decided to cancel the entire Earth.
Re: (Score:2)
No, it's the pollution and with CFCs being banned, good deodorants are hard to find.
Re: (Score:2)
No. The moon is moving away by using the energy from slowing the Earth's rotation.
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The rate at which the Earth slows will go down, but the slowdown will continue until both bodies are tidally locked and the same face of Earth always faces the moon. (The moon is already tidally locked.)
At that point the Moon will then slowly start drifting back toward Earth for reasons I don't remember, and eventually crash into Earth. I don't know if Earth's rotation will also speed up as it comes closer. But by then the Sun will swell and probably kill the moon, and maybe Earth. Better buy a house in ano
Re: Another example of Climate Change! (Score:2)
I stopped eating people quite a while ago, tyvm!
UT1-UTC (Score:2)
Unlikely, like the chance of you winning the recent lottery. UT1-UTC is in the neighborhood of -100 ms, so it's going to be a while before there's another leap second.
Re: UT1-UTC (Score:2)
More like -60ms and getting more positive for the last year or so. If it breaks +700ms then we'll need a negative leap second. That's going to break some software.
Re: (Score:2)
The most recent USNO number [navy.mil] (1Jul22) is -0.0381740 s with possible error of 0.0000157 s The number I gave was from NIST's most recently published data [nist.gov].
The prediction is it will be around 7 ms at the end of the year, and it's already been announced [iers.org] that there will be no leap second this year.
Negative leaps should actually be easier to handle, because their enumeration fits in the traditional 0:0:0 - 23:59:59 system.
Re: (Score:2)
If you want to try correcting someone, you should at least be correct.
The most recent USNO number [navy.mil] (1Jul22) is -0.0381740 s with possible error of 0.0000157 s
From your source, the number for 1 Jul is -0.0686587s. The figure you've given is for July 31.
Re: (Score:2)
Jeez! I hope we all don't fly off the planet! (Score:1)
Re: (Score:2)
;-) Just kidding!
So you do hope we do?
No more 1-second insertions? *wink* *nudge* (Score:1)
Not just "unlikely"; officially ruled out. (Score:2)
The next opportunity is in December 2022, although with Earth spinning so fast of late, it is unlikely to be needed.
NO leap second will be introduced at the end of December 2022. [iers.org] The bulletin is dated 5 July 2022.
Moon? (Score:2)
How much do we contribute by extracting oil and other minerals from the depth and putting it into the air as co2? That's also moving mass away from the center, it should have a slowing effect.
Re: (Score:2)
To put it mildly, it's unlikely that anything we do to the 10ish kilometers deep down and up high that we can actually affect directly will have any impact on a planet that's 12,700 kilometers in diameter.
It's an amazing thing about primordial Earth (Score:3)
Re: (Score:2)
*pictures a dinosaur on a surfboard
Mass Moves Inwards (Score:2)
Water flows down.
And just like the ice skater puling mass inwards the rotational speed picks up.
QED
Leap seconds are an abomination (Score:1)
Not the idea of keeping civil time in synch with the sun, but the way it's implemented.
Google supposedly stretched out the standard second on leap days, so that there would still be 86400 seconds on a leap day, but they weren't SI seconds, they were 1+1/86400 SI seconds each.
God help you if you were running any kind of measurement inside Google that required accurate time and you were synching to their clocks.
Re: (Score:2)
If you are doing any sort of time calculation, you should take into consideration that sometimes clocks are inaccurate, sometimes they leap forward, and sometimes they leap backwards. If your algorithm can't handle that, be sure to use a monotonically increasing clock function.
Reference point? (Score:1)
I guess they use the sun as a reference point.
In half a year the earth have rotated half a revolution more or less (don't know which, I think it's more) because otherwise a revolution starting midday would mean midnight on the other side of the sun. I hope they accounted for this some way. Either defining a revolution as when the sun is over the same longitude, or a 360 degree turn, but if they talk about the length of day I guess the former.