The spelling of the term "mean solar day" is derived from the International Phonetic Alphabet (IPA) phonetic transcription. In IPA, "mean" is /miːn/ and "solar" is /ˈsəʊlə/. "Day" is spelt as it is, but is pronounced as /deɪ/. A mean solar day refers to the average length of a day, which is used as a standard reference for measurements of time. This value is determined based on the rotational motion of the earth relative to the sun.
A mean solar day is a term used in astronomy and timekeeping to define the average length of a day on Earth. It refers to the period of time it takes for the Earth to complete one full rotation on its axis in relation to the Sun. This duration is typically measured from noon on one day to noon on the following day.
The term "mean" in mean solar day indicates that it is an average value rather than a fixed or constant length of time. This is because the rotation of the Earth can vary slightly due to numerous factors, including gravitational forces from other celestial bodies, the Earth's elliptical orbit around the Sun, and tidal interactions.
To calculate the mean solar day, scientists make use of precise measurements of the Earth's rotation over an extended period of time. These measurements are then averaged to determine the length of a typical day. Currently, the mean solar day is considered to be approximately 24 hours long, or more precisely, 24 hours, 3 minutes, and 56.555 seconds, based on the International System of Units (SI).
The concept of a mean solar day is crucial for coordinating timekeeping systems around the world, such as the Coordinated Universal Time (UTC), which is based on atomic clocks but adjusted to remain in line with the average length of a mean solar day.