Today is the longest day of the year as June 21 marks the summer solstice. It’s the day when there are the most hours of sunlight.
The summer solstice occurs when the tilt of a planet's semi-axis, in either the northern or the southern hemisphere, is most inclined toward the star that it orbits. Earth's maximum axial tilt toward the Sun is 23° 26'. This happens twice each year, at which times the Sun reaches its highest position in the sky as seen from the north or the south pole.