A fictitious body that moves eastward in a circular orbit along the celestial equator, making a complete circuit with respect to the vernal equinox in a tropical year. It is the moving point chosen in defining mean solar time.
An imaginary Sun travelling at a speed equal to the average rate that the real Sun travels along the ecliptic.
[n] - a theoretical sun that moves along the celestial equator at a constant speed and completes its annual course in the same amount of time the real sun takes at variable speeds
noun a theoretical sun that moves along the celestial equator at a constant speed and completes its annual course in the same amount of time the real sun takes at variable speeds