Winter Solstice 2020: What You Need to Know About the Shortest Day of the Year

The 2020 winter solstice was official at 5:02 a.m.ET / 2:02 a.m. PT on Monday, December 21, marking the official start of the astronomical winter and the shortest day of the year for the Northern Hemisphere. In the Southern Hemisphere, that day is the summer solstice and the longest day of the year.

The 23.5 degree tilt in the Earth’s axis of rotation causes the sun to rise and set over the course of a year. During the winter solstice, the Northern Hemisphere tilts as far from the sun as possible, creating less light and colder temperatures.

The tilt of the earth – not our distance from the sun – is the cause of winter and summer. In fact, the Earth is closer to the sun in the winter than it is in the summer months.

The solstice isn’t the only major astronomical event on Monday.

During Monday’s “great conjunction”, Jupiter and Saturn will form a “double planet” that appears only one-tenth of a degree apart – or about the thickness of a dime at an arm’s length.

This phenomenon is called a “Christmas Star,” referring to the heavenly light that led the three wise men to Jesus in the Christmas story of the Christian Bible.

Skywatchers can distinguish Saturn and Jupiter from the stars because the planets appear “brighter and firmer in the sky.”