History · The Sun
Gnomon
Say it: NOH-mon IPA: /ˈnoʊmɑn/ noun
Gnomon: The part of a sundial or related instrument that casts a shadow used for measurement.
A rod or edge casts a shadow that changes as the Sun moves across the sky. Reading that shadow against markings can indicate solar time.
- Example
- The gnomon's shadow crossed the noon mark.
- Why astronomers use it
- Shadow measurements connect apparent solar motion with time, latitude, and geometry.
- Tiny cosmic connection
- A sundial does not automatically agree with a civil clock; longitude, the equation of time, and daylight saving can matter.
Observatory History The Sun
Where to check it
Written for Cool Moon Facts in its own words; the sources cover the same idea in more depth.