The concept.
Time is space: a clock that shows, at a glance, where you stand in the day, the year, and the solar system.
Noon is the top of the clock. But because the Earth orbits the Sun, the Sun appears to drift all the way around the celestial sphere over the course of a year, along the line we call the ecliptic. To keep it pinned to the top, the whole sky map quietly turns the opposite way, once per year.
Almost everything else follows from that one decision. The map runs counterclockwise, matching the Earth’s spin seen from the north. Your time zone becomes a meridian sweeping across it. The Moon and planets ride the ecliptic at their true angles from the Sun, so the face doubles as a map of the sky above you.
This page is still growing. For the complete, visualized walkthrough of every convention – and the astronomy behind it – see the astronomy deep dive.