This year’s first official day of summer will fall on June 20. Summer solstice, also called June solstice or midsummer, is the point in time when the Earth’s orbit arrives at a point where the North Pole is at its maximum tilt towards the sun. Making this day the longest day and the shortest night of the year.

When the northern hemisphere is experiencing the start of summer, it’s the exact opposite for the southern hemisphere. This day is when the sun is at its lowest point in the sky for the southern part of the globe, signaling the start of winter.

The sun’s rays strike the earth at a more direct angle, causing a warming effect that we have all come to know as summer. It’s also the reasoning behind this day receiving the longest period of sunlight during the entire year.

This year the summer solstice will occur at 3:43 p.m. Mountain Daylight Time.