Solar Time
Sun time. Time marked by the diurnal revolution of the earth with regard to the sun. A mean solar day is the average length of all the solar days in the year. The difference between true and mean time is called the equation of time. There are only four days in the year when the apparent and mean time are the same, and the equation of time nothing. These are December 24th, April 15th, June 15th, and August 31st. Between December 24th and April 15th, and between June 15th and August 31st, the apparent is always before the mean time, whilst in the remaining interval it is later.