Theantisolar point is theabstract point on thecelestial sphere directly opposite theSun from an observer'sperspective.[1] This means that the antisolar point lies above thehorizon when the Sun is below it, and vice versa. On asunny day, the antisolar point can be easily found; it is located within theshadow of the observer's head. Like thezenith andnadir, the antisolar point is not fixed inthree-dimensional space, but is defined relative to the observer. Each observer has an antisolar point that moves as the observer changes position.
The antisolar point forms thegeometric center of severaloptical phenomena, including subhorizonhaloes,rainbows,[2]glories,[3] theBrocken spectre, andheiligenschein. Occasionally, aroundsunset orsunrise,anticrepuscular rays appear to converge toward the antisolar point near the horizon.[4] However, this is anoptical illusion caused by perspective; in reality, the "rays" (i.e. bands of shadow) run near-parallel to each other.[5]
Also around the antisolar point, thegegenschein is often visible in a moonlessnight sky away fromcity lights, arising from thebackscatter ofsunlight byinterplanetary dust. Inastronomy, thefull Moon or aplanet inopposition lies near the antisolar point. During a totallunar eclipse, the full Moon enters theumbra ofEarth's shadow, which the planet casts ontoits atmosphere, into space, and toward the antisolar point.
Theanthelic point is often used as a synonym for the antisolar point, but the two should be differentiated.[1]While the antisolar point is directly opposite the sun, always below the horizon when the sun is up, the anthelic point is opposite but at the same elevation as the sun, and is therefore located on theparhelic circle. There are severalhalo phenomena that are centered on or converge on the anthelic point, such as theanthelion, Wegener arcs, Tricker arcs and the parhelic circle itself.[6][7][8]
