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Celestial Horizon Diagram
HK defaultYour celestial horizon
The celestial horizon is the great circle halfway between the zenith (straight up) and nadir (straight down). It divides the sky you can see from the half you cannot.
Side view of observer
Before you start
Your personal horizon divides the visible sky from the hidden half. On the celestial sphere, it's a great circle tied to your location.
Key idea
Zenith is straight up; nadir is straight down. The celestial horizon is 90° from both. Your latitude equals the altitude of the celestial pole.
What you see
- Side-view diagram: zenith, horizon, observer, celestial pole direction
- Latitude and LST controls
Try this
- Set latitude to Hong Kong — pole altitude matches latitude
- See how the horizon plane tilts with latitude
- Relate this to why Polaris height equals your latitude
Why it matters in Hong Kong
In HK, Polaris is only 22° above the northern horizon — the celestial pole sits low in our sky.
Common mistakes
- Confusing true horizon with sea horizon (refraction matters)
- Thinking everyone sees the same sky hemisphere
Glossary
- Zenith
- Point directly overhead.
- Celestial horizon
- Great circle 90° from the zenith.