[bombcar]

that's basically it

we want to be able to say "in the morning" and have it be reliably interpreted, because most human activities are actually tied to the sun and not to the clock (the clock is incidental for precise timing, but it's just reflecting the sun position).

[makeitdouble]

The part that's really weird to me is those lines are latitude based, so Finland and South Africa share the same timezone.

Sun wise, situations are a pretty different at any moment in the two countries. I wouldn't call the system "reliable" ( and those are not outliers, any zone with countries on opposite hemispheres has the same issue)

[rypskar]

>>Sun wise, situations are a pretty different at any moment in the two countries

The sun is still at its high point at the same time of the day in both countries

[brightlancer]

> The sun is still at its high point at the same time of the day in both countries

No.

Helsinki's solar noon is about 35 minutes later than Cape Town's and 100 minutes later than Pretoria's.

This is normal, because time zones are mostly broken into non-uniform 1 hour increments across 180 degrees of latitude.

[garrickvanburen]

yep - timezones are not straight lines - namely around the international date line.

[makeitdouble]

Doesn't that presume the earth is perfectly turning around its North/South axis ?

[mixmastamyk]

How would a rock spin other than "perfectly?"

[makeitdouble]

It was more about the spin axis: timezones are vertically cut on a South/North line, while the earth rotation deviates from there.

I actually couldn't find how much it deviates. I assume there's variation depending on the seasons as well.

[mixmastamyk]

Not really, there’s a tiny bit of wobble but it moves over a thousands years or so, nothing to worry about. The axis doesn't change to my knowledge.

https://en.m.wikipedia.org/wiki/Axial_precession

Magnetic poles changing is not relevant it seems.