Winter solstice is an astronomical phenomenon which marks the shortest day and the longest night of the year. Winter solstice occurs for the Northern Hemisphere in December and for the Southern Hemisphere in June (quoted from the Wikipedia). The Sun’s northward movement (Uttarayana) starts a day after winter solstice on December 22nd, and lasts for 6 months until the summer solstice in June. These astronomical events have deep cultural and spiritual significance in many parts of the word. According to Hindu tradition the six months of Uttarayana are a single day of the Gods; the six months of Dakshinayana are a single night of the Gods (quoted from the Wikipedia). It is believed that when a person dies during Uttarayana, the soul reaches the Gods. That is why Bhishma Acharya waited several weeks on “ampasayya”, the bed of arrows, until his liberation in Uttarayana. The Kurukshetra war started on Kartheeka Bahula Amavasya (around November) and lasted for 18 days in the present day Haryana. According to scriptures, the Murhurtham for the Kurukshetra war was chosen by Lord Krishna. It is interesting that the time of the year chosen (November) is well suited for the war, compared to the summer, which will cause rapid physical exhaustion.
The following link shows an amazing photograph of sun’s hairpin at the winter solstice.