'n Dag is die relatiewe eenheid van tyd wat die periode beskryf wat dit 'n planeet neem om om sy eie as te draai.
One day of solar time, the time between successive noons; the time in which a planet such as Earth apparently rotates once around its axis, relative to the sun (on Earth about 24 hours as an average - the length of solar day is not constant throughout the year).