Celestial Equatorial HC

Note: Similar to Celestial vs Horizon Comparison — NAAP version with more detail.

NAAP horizon–celestial comparison. Hour angle and local sidereal time (LST) sit on the equatorial system; altitude sits on the horizon system. Default: Hong Kong.

Latitude: 22.32°Hour angle: 0°Declination: 23.50°LST: 12.00 h

Altitude ≈ 88.8° · LST 12.0h · RA ≈ LST − HA/15

Before you start

NAAP side-by-side of horizon coordinates and equatorial coordinates, with hour angle and local sidereal time.

Key idea

Altitude depends on where you stand and what time it is. Declination does not. Hour angle is how far a star is from the meridian.

What you see

Horizon disk and celestial sphere
Latitude defaulted to Hong Kong
LST and hour-angle sliders

Try this

Set declination equal to Hong Kong’s latitude — the star can pass through the zenith
Change hour angle and watch altitude drop
Compare with the simpler Celestial vs Horizon Comparison lab

Why it matters in Hong Kong

Polaris is only ~22° up from Hong Kong, not overhead as in higher northern latitudes.

Common mistakes

Using altitude as if it were a star-catalogue coordinate

Glossary

Hour angle: Angular distance west of the meridian.
LST: Local sidereal time — the RA currently on the meridian.