) is a faint brightening of the night sky in the region of the zodiac
directly opposite the Sun
caused by reflection of sunlight by small dust particles that lie in the plane of the Solar system
. It appears as a softly glowing oval region a few degrees wide and 10-15° in length, oriented along the plane of the ecliptic
. It is so faint that it cannot be seen if there is any moonlight
or if it falls in the vicinity of the Milky Way
The gegenschein is one of several skyglows that also include the zodiacal light and the zodiacal band.
See Optical phenomenon.