Time just is, until it isn’t
Celestial bodies are in constant motion. There is no fixed position in space from which one can observe absolute motion. Since all motion is relative, the position of the observer must be noted when discussing stellar motion. From the Earth, we see apparent motions of celestial bodies on the celestial sphere. In considering how stars follow their orbits around galaxies, we assume a hypothetical observer at some distant point in space.
Traditionally, astronomy has furnished the basis for the measurement of time, a subject of primary importance. The year is associated with the revolution of the Earth in its orbit. The day is one rotation of the Earth about its axis.
The universe doesn't include a convenient sheet of graph paper at absolute rest that we can trace paths on. The best we can do is use distant stars (sidereal). Time literally means "star time." The sidereal day is the time required for the Earth to rotate once relative to the background of distant stars—The period from one vernal equinox to the next.
- A second is 1/86,400 of the time that it takes the Earth to rotate once on its axis. With 24 hours in a day, 60 minutes per hour, and 60 seconds per minute, there are 86,400 seconds in a day. There has never been a more accurate definition for the second, and there never will be.
Give me a sec. It’s the second small part of an hour. The Latin for the first small part is "pars minuta prima," meaning they divide the hour by minutes first. Latin for the second small part is "pars minuta secunda." That is, they divided the hour by the number of seconds in a second. Since then, we’ve just been refining the accuracy of what we call a second.
October 5th to October 14th never happened in 1582. No one was born;
No one died;
Nothing happened.
And from September 3rd to September 13th, 1752, nothing was seen.