Today is summer solstice! It is the day of the year with the longest daylight period and hence the shortest night. This day usually occurs on June 21/June 22 in the northern hemisphere and on December 21/December 22 in the southern hemisphere. This year it has fallen on june 21.
At the time of summer solstice, the earth's is in such a position that one hemisphere is most tilted towards the sun, causing the sun to appear at 23.45 degrees above the celestial equator, thus making its highest path across the sky.
During the summer solstice in nothern hemisphere the sun appears to be directly overhead at midday along an imaginary line on the Northern Hemisphere at latitude 23.45 degree north known as the Tropic of Cancer.Similarly during the summer solstice in southern hemisphere the sun appears to be directly overhead at midday along the imaginary line Tropic of Capricorn.