noun
mean sun
Astronomical term: a hypothetical sun that moves uniformly along the celestial equator, used as a reference for mean solar time.
平均太陽は、実際の太陽の動きを平均化した仮想的な天体です。
The mean sun is a hypothetical celestial body that averages the motion of the actual sun.
真太陽 (true sun) refers to the actual observed sun, while 平均太陽 is the idealized uniform-motion sun used for timekeeping.
Compound of 平均 (mean, average) and 太陽 (sun), a calque from Western astronomical terminology.