sol·stice (sōlstĭs, sŏl-, sôl-)
Either of two times of the year when the sun is at its greatest angular distance from the celestial equator. The summer solstice in the Northern Hemisphere occurs about June 21, when the sun is at the zenith on the Tropic of Cancer; the winter solstice occurs about December 21, when the sun is at zenith on the Tropic of Capricorn. The summer solstice is the longest day of the year; the winter solstice is the shortest.
[Middle English, from Old French, from Latin sōlstitium : sōl, sun; see sāwel- in the Appendix of Indo-European roots + -stitium, a stoppage; see stā- in the Appendix of Indo-European roots.]
sol·stitial (-stĭshəl) adj.
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