The first day of Winter or winter solstice occurs at the instant when the Sun's position in the sky is at its greatest angular distance on the other side of the equatorial plane from the observer's hemisphere. The seasonal significance of the winter solstice is in the reversal of the gradually lengthening nights and shortening days. Depending on the shift of the calendar, the winter solstice occurs sometime between December 20 and December 23 each year in the northern hemisphere, and between June 20 and June 23 in the southern hemisphere, during either the shortest day or longest night of...