Sunup is the moment when the sun first appears above the horizon in the morning, marking the start of a new day. It's another word for sunrise or dawn. When farmers say they'll start work at sunup, they mean they'll begin as soon as there's enough natural light to see by.

The word captures something practical and natural: for most of human history, people organized their days around sunup and sundown rather than checking clocks. Before electric lights, sunup meant it was time to wake up, start the fire, and begin the day's work. Even today, hikers planning an early trail start might say they're leaving at sunup to catch the cool morning air and the beautiful light.

You might see the phrase from sunup to sundown in stories about people who work long, hard days outdoors. It means working from first light until the sun disappears below the horizon in the evening. The opposite of sunup is sundown, when the sun drops below the horizon at night.