Today is the longest day of the year which is called the summer solstice. It marks the official start of summer and has spiritual significance to many. The summer solstice is when the sun reaches its highest point in the sky. Following the solstice, the days gradually begin to get shorter until the winter solstice, the shortest day of the year.

In terms of astronomy, the June solstice has to do with the tilt of the Earth's axis and an imaginary line circling the globe called the Tropic of Cancer, which marks the most northerly latitude where the sun can be directly overhead, according to NASA. The solstice occurs when the sun is directly over the Tropic of Cancer.