the time during the year when the sun is at its highest or lowest point in the sky, typically around June 21 or December 21

सौर द्विवर्षीय

English Usage: The summer solstice marks the longest day of the year.

Hindi Usage: गर्मी के संक्रांति का दिन वर्ष का सबसे लंबा दिन होता है।