The science and celebration of the Summer Solstice Scott Sutherland Saturday, June 20, was the summer solstice for 2020 - the official first day of summer in the northern hemisphere and the longest day of the year for this half of the planet. Why is OPPOSITE DAY winter solstice, the first day of winter, and the shortest day of the year. This is due to the northern and southern hemispheres experiencing opposite seasons, no matter what time of year it is. A SOLAR 'PAUSE' solstitium, which basically means "Sun ( sol) stoppage ( stitium)". It refers to how the Sun appears to 'stop' or 'pause' in the sky on this day.