The Winter Solstice falls on Wednesday, December 21, 2016 at 10:44 a.m. Universal Time (5:44 a.m. Eastern Time), according to the U.S. Naval Observatory.

What is the Winter Solstice?

The Winter Solstice, as pictured in the above NASA image, is caused by a tilt of the earth’s rotating axis and marks the first day of winter. It is the shortest day and longest night of the year in the northern hemisphere for locations like Melbourne, Florida, but the reverse happens in the southern hemisphere for locations such as Melbourne, Australia.

The Winter Solstice can occur on December 20, 21, 22, or 23, depending on calendar events such as leap year and when the Solstice begins relative to Coordinated Universal Time.

According to NASA, it is not the Sun that is moving north or south through the seasons, but a change in the orientation and angles between the Earth and its nearest star. The axis of the Earth is tilted 23.5 degrees relative to the Sun and the ecliptic plane. The axis is tilted away from the Sun at the December solstice and toward the Sun at the June solstice, spreading more and less light on each hemisphere. At the equinoxes, the tilt is at a right angle to the Sun and the light is spread evenly.