Because of that tilt, the Northern and Southern Hemispheres are tilted either toward or away from the sun at different times of the year as the Earth makes its orbit around its closest star.
The upside is that after the winter solstice, daylight hours will become longer - eventually.
This marks the day with the shortest duration of daylight in the northern hemisphere.
In the south, it's just the reverse though.
The first day of winter, Friday, Dec. 21, will not be your typical winter solstice.
This year's Winter Solstice will coincide with a Full Cold Moon - the full moon of December, according to Space.com.
To talk about the science behind winter solstice, it marks the shortest day in the Northern Hemisphere since the sun is positioned at its most southerly position while directly overheating at the Tropic of Capricorn.
The Ursid meteor shower will peak on Friday night.
December's full moon has earned the nickname of the Cold Moon.
The Ursids meteor shower will be visible tonight.
A full moon will occur December 22, bringing a bright light to the start of winter. We will also see our final meteor shower of the year.
People around the world have celebrated this astronomical milestone for centuries.
In Ireland, people convene at a 5,000-year-old gravesite called Newgrange, where they wait for a chance to see the sunrise lighting up the tomb. In England, crowds gather at Stonehenge to capture the moment with the sun directly aligns with the ancient stones, Google notes in its blog post.
Winter Solstice in China is referred to as the "Dongzhi festival, ', a celebration of winter's arrival".
The festive food is said to bring prosperity and unity among families. It's really a case of "Sunny side down" for the Earth today!