If you think that can get complicated, check out the different global geodetic reference systems. Between the Earth's precession, plate tectonics, the Earth changing mass cyclically (collecting space debris and off-gassing atmosphere), and the fact that the center of our planet is a freaking wobbly blob of molten iron, well, things can get tricky.
Then there are the different eliosoidal (and soon geoid with NVD22) shapes that are the basis for every other reference system, most based on similar, but slightly different geodetic network adjustments. Some systems, like NAD83, remain relatively fixed in reference to a particular land mass (North America Datum 1983). Some will then progress with the land mass as it moves on the Earth's plates, others will remain fixed based on a (the) prime meridian, or in reference to the center of gravity of the Earth as it shifts, or in reference to Polaris, etc.
So now you have multiple measuring systems each referencing different geometric/geodetic/astronomic points/lines, and further it matters what time it was when you defined those points/axises. WGS80 is the basis for many modern systems, including NAD83. ITRF is similar, but defines a yearly amount of progression since ~1980 to account for things like continental drift. They coincided around the time when they were defined, and have been diverging some number of millimeters per year since then.
Once you agree on a definition of a system, you further have to define how to measure it. Will North be a point in time, or a rolling average? Will the center of gravity of the Earth be based on changing rate of Earth's rotation, or with respect to a geodetic benchmark or network, or maybe based on millimeter fluctuations in deviations of the orbits of the NAVSTAR / GPS satellites? Should Euro/ Chinese/ Russian / Indian versions of GPS satellites be taken into account?
I'm over simplifying things, as there are additional layers of complexity involving the actual tools for surveying and measurement, the precise steps for any network adjustments or translations, rounding rules and certain geometric assumptions made for different types of math, and way, way more. (You can't actually stretch a tape measure around the equater.)
Take all of that, and then contemplate how all of this is spinning around arbitrarily in space. Sidereal vs solar is only one of 100s of aspects of how we measure these things. It's not just time, but also geometric space.
Also, you can try to explain this to people, most of whom will complain that it's way too complicated, and we don't need anything to be that precise. They say it's ridiculous.
Then you can ask the same person for directions to their house, and they'll turn around and text you GPS coordinates to 12 digits.
Then there are the different eliosoidal (and soon geoid with NVD22) shapes that are the basis for every other reference system, most based on similar, but slightly different geodetic network adjustments. Some systems, like NAD83, remain relatively fixed in reference to a particular land mass (North America Datum 1983). Some will then progress with the land mass as it moves on the Earth's plates, others will remain fixed based on a (the) prime meridian, or in reference to the center of gravity of the Earth as it shifts, or in reference to Polaris, etc.
So now you have multiple measuring systems each referencing different geometric/geodetic/astronomic points/lines, and further it matters what time it was when you defined those points/axises. WGS80 is the basis for many modern systems, including NAD83. ITRF is similar, but defines a yearly amount of progression since ~1980 to account for things like continental drift. They coincided around the time when they were defined, and have been diverging some number of millimeters per year since then.
Once you agree on a definition of a system, you further have to define how to measure it. Will North be a point in time, or a rolling average? Will the center of gravity of the Earth be based on changing rate of Earth's rotation, or with respect to a geodetic benchmark or network, or maybe based on millimeter fluctuations in deviations of the orbits of the NAVSTAR / GPS satellites? Should Euro/ Chinese/ Russian / Indian versions of GPS satellites be taken into account?
I'm over simplifying things, as there are additional layers of complexity involving the actual tools for surveying and measurement, the precise steps for any network adjustments or translations, rounding rules and certain geometric assumptions made for different types of math, and way, way more. (You can't actually stretch a tape measure around the equater.)
Take all of that, and then contemplate how all of this is spinning around arbitrarily in space. Sidereal vs solar is only one of 100s of aspects of how we measure these things. It's not just time, but also geometric space.
Everything's relative.