The winter solstice occurs at the instant when the Sun's position in the sky is at its greatest angular istance on the other side of the equatorial plane from the observer. Depending on the shift of the calendar, the event of the winter solstice occurs some time 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 the longest night of the year, which is not to be confused with the darkest day or night or the day with the earliest sunset or latest sunrise. Though the Winter Solstice lasts an instant, the term is also used to refer to the full 24-hour period.