"Mm," he hums in understanding. "Humans used to do that, too. They'd tell what time of day or even what part of the year it was based on the sun and moon and light and cold and plants and animals around them. But they invented clocks and made up new ways to divide time."

As they continue walking, Su-jin points up again, this time just quickly. "The time we see the sun is day and the time without it is night. Days and nights are divided into smaller segments called hours. Noon is one such hour. Does that make sense?"