June 21 is the Longest Day and the Shortest night in Northern hemisphere. Due to Tilted on it's Axis and Rotation around the Sun the position of the Earth is Different in different seasons in the year. The Northern Hemisphere tilted towards Sun in Summer (June 21st) and The Southern Hemisphere tilted towards Sun in Winter (December 22nd).
The summer solstice happens every year between June 20 and June 22 when the sun reaches its highest elevation in the Northern Hemisphere, making it the longest day of the year with a stretch of sunlight that lasts for 17 hours.
The term solstice derives from Latin word “sol” meaning “sun” and “sistere” which means “to make stand, ”
Earth Seasons
Summer Solstice - when Sun is directly over Tropic of Cancer on June 21st.
