What is up or down? What if it changed?

what is up down spaceWhen you are standing on planet Earth how do you define what is up and down?

Up would be upwards to the sky, heavens, stars?

Down would be downwards into the Earth itself?

If you dug down through the Earth where would you appear? In Australia or Europe?

magnetic reversal earth what up downIn Australia is up towards the North pole as that is where we have magnetic North? Or where western convention says it is.

Space up and down?

Up or down in space does not really exist.

Especially as earth and most of the planets, for some mysterious or electromagnetic reason, orbit around the Sun on a similar plane.

geomagnetic reversal earth what up down

Earth up and down change?

earth magnetic field reversal what up downBut what if you lived a few thousand years ago and the stars were flipped or moved massively in the sky?

What if you lived in Europe but suddenly one night you could see only a few of your normal stars low on the horizon and the sky was filled with strange stars, that you perhaps knew were previously only seen from a different part of the world, or you did not even know that?

Was it the stars or solar system that has changed/moved or would it be the planet Earth itself? What then would then be up or down? Or was up still up and down still down?

But how would you inform those born after the event what had happened? How would you explain it or refer to it for future generations? How would you communicate to those who lived during the event about previous dates, would it have to be referred to as pre or post?