You can be forgiven for thinking that winter has already begun - given the snow storms that hit US cities from Washington to Boston over the weekend- but actually, winter only officially begins on Monday with the Winter Solstice.
The Winter Solstice occurs at 12:47 p.m. EST (1747 GMT) on Monday, which marks the beginning of winter for the Northern Hemisphere.
When the Winter Solstice begins, that is when the earth’s axial tilts, putting the earth at its furthest position from the sun.
As the earth rotates around the sun on its tilted axis, the Northern Hemisphere appears to move away from the Sun this time of year.
The Winter Solstice also marks the shortest day of the entire year, as it will be getting darker earlier tonight and getting lighter later than normal tomorrow morning.
This is because the Northern Hemisphere appears to move away from the Sun at this time of year, which results in less direct sunlight, shorter days and colder temperatures.