What is a Gnomon?

There is a term for everything. For example, that little plastic sleeve on the end of your shoelace is an aglet, probably invented by Harvey Kennedy in 1790 (https://en.wikipedia.org/wiki/Aglet).


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So yesterday when I was reading about astronomy, I found a word that piqued my interest — gnomon. According to Miriam-Webster (https://www.merriam-webster.com/dictionary/gnomon), it’s “an object that by the position or length of its shadow serves as an indicator especially of the hour of the day.” This means the column in the middle of a sundial is a gnomon. It can also be a column or shaft perpendicular to the horizon. There is also a mathematical definition, “the remainder of a parallelogram after the removal of a similar parallelogram containing one of its corners,” but math is not my best subject, so I’m not going there.

Gnomons were important in history because they were used by the early Chinese to determine changes in the seasons, find latitudes, and even to create calendars based on shadow measurements (https://en.wikipedia.org/wiki/Gnomon). You can learn a lot about the universe just by studying the sun’s shadow, and for that you need a gnomon.

I guess the lesson here is everything has a name.

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