The simple truth is that we haven’t a clue as to why the earth spins, how it started spinning and why the speed of spin varies.
These are all recent headlines.
Earth spinning faster.
Earth spinning slower
Why does the earth rotate in 24 hours? It’s just magic
June 26, 2017
The rotational speed of a planetary body around its own axis is primarily set by the angular momentum the mass of matter making up the body had when it first coalesced into a planet. What determined that initial angular momentum is unknown. All known effects thereafter (mainly tidal and all fundamentally gravitational effects) slow this rotation. For the last 3,000 years the earth’s rotation has been slowing down to cause the day to lengthen by about 2 milliseconds per century.
Currently the solar (siderial) day has a mean value of about 2 milliseconds greater than 86,400 seconds while the stellar day (relative to the fixed stars) has a mean value of about 86, 164 seconds.
But we have no real understanding of why it is what it is. ……
We can observe that the day length on the planets are:
…….. The laws of physics (as we know them) did not apply at the Big Bang singularity. All the energy (dark, imaginary and real) in the universe and all the momentum in all the materia (dark or otherwise) making up the universe was determined in the singularity when the laws of physics did not apply. How the Big Bang caused matter to gain spin in the first place is also unknown. So the simple answer to why earth’s day is 24 hours long (and why any planet’s rotational speed is what it is) is that we haven’t a clue.
It’s just magic.
It used to be that a second was defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each (24 × 60 × 60 = 86400). But the day is now taken to be 86 400 seconds where a second is now defined as the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium-133 atom.
“Caesium is a relatively rare element, estimated to average 3 parts per million in the Earth’s crust. Caesium (55Cs) has 40 known isotopes, making it, along with barium and mercury, one of the elements with the most isotopes. The atomic masses of these isotopes range from 112 to 151. Only one isotope, 133Cs, is stable”.
The very concept of a day derives from the spin of the earth. Of course, if a day was still defined as the period of the earth’s rotation around its own axis and and not as a multiple of the second, there would be no need to have any headlines.
I wonder sometimes whether a second now is longer than a second was then.
And how would we know?
Tags: Planetary spin
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