The term "solar day" refers to the time it takes for the Earth to complete one rotation around its axis. Other words that can be used interchangeably with this term include diurnal period, daylight period, or simply a day. The length of a solar day varies throughout the year due to the elliptical orbit of the Earth around the sun and the tilt of its axis. It ranges from 23 hours 59 minutes and 38 seconds to 24 hours and 30 seconds. Despite variations in length, the solar day is the standard measure of time used by humans and is critical for activities such as agriculture, navigation, and scientific research.