The winter solstice doesn’t coincide with the coldest day of the year due to Earth’s axial tilt and its ability to retain heat.The darkest day of the year—featuring the least amount of sunlight and the longest night—is the winter solstice. However, the coldest period of the year typically occurs about a month after the solstice. This delay is explained by Earth’s axial tilt and the way it absorbs and releases heat, according to Live Science.