The winter solstice is the day that marks the shortest period of sunlight and the longest period of nightfall for the northern hemisphere. It is also called ‘midwinter,’ and ‘longest day.’
This is when the Earth is tilted farthest away from the Sun in its orbit. This happens twice a year, and it is opposite for each hemisphere. From the Earth, this is when the Sun seems highest in the sky.
In the southern hemisphere, these quarter days are opposite to each other, and the midwinter for the northern hemisphere is actually midsummer for the south.