noun
subsun; undersun
A halo phenomenon where a bright spot appears directly below the sun, caused by sunlight reflecting off ice crystals in the atmosphere. Technical term used in meteorology and atmospheric optics.
映日は、太陽の真下に見える光の現象です。
A subsun is a light phenomenon seen directly below the sun.
飛行機から映日を観測することがあります。
Subsuns are sometimes observed from airplanes.
Compound of 映 (ei, 'reflect') and 日 (jitsu, 'sun'), literally 'reflected sun'. The term is a direct calque from English 'subsun' or 'undersun', describing the reflected image of the sun below the horizon.