<Tr> <Th> Frequency </Th> <Td> Twice a year (once in the northern hemisphere, once in the southern hemisphere, six months apart) </Td> </Tr> <Tr> <Th> Related to </Th> <Td> Winter festivals and the solstice </Td> </Tr> <P> The winter solstice (or hibernal solstice), also known as midwinter, is an astronomical phenomenon marking the day with the shortest period of daylight and the longest night of the year . It occurs when one of the Earth's poles has its maximum tilt away from the Sun . It happens twice yearly, once in each hemisphere . In the Northern Hemisphere this is the December solstice and in the Southern Hemisphere this is the June solstice . </P> <P> The axial tilt of Earth and gyroscopic effects of its daily rotation mean that the two opposite points in the sky to which the Earth's axis of rotation points (axial precession) change very slowly (at the current rate it would take just under 26,000 years to make a complete circle). As the Earth follows its orbit around the Sun, the polar hemisphere that faced away from the Sun, experiencing winter, will, in half a year, face towards the Sun and experience summer . This is because the two hemispheres face opposite directions along Earth's axis, and so as one polar hemisphere experiences winter, the other experiences summer . </P>

When is the darkest day of the year
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