Word origin · etymology
Latin through Middle English.
Latin altitudo means height, from altus, high. Astronomical altitude preserves this vertical sense as an angle above the horizon.
How we know · epistemology
Local observational geometry
Altitude is calculated relative to a local horizon. Atmospheric refraction changes apparent altitude near the horizon, so a geometric result and an observed sighting need not coincide exactly.
Connected concepts
Sources & provenance
Use the citations beside each section to distinguish a calculation convention, a historical teaching and an editorial example.