When Does Winter Solstice Occur

Even though the December solstice, i.e. the winter solstice in the United States and other regions of the northern hemisphere, has immense scientific and cultural significance, not many people out there actually know what this phenomenon is all about.

As per the definition, it is an astronomical event which occurs when the Sun is at its southernmost extreme at the 23.5°S (Tropic of Capricorn) latitude. While this precise moment marks the winter solstice for the northern hemisphere, for the southern hemisphere it is the summer solstice.

As weird as it may sound, this can be attributed to the fact that both hemispheres have different seasons at any given time of the year. These are developed from an inferior ovary as opposed to true berries that develop from a superior ovary. These are also called false berries.

While the month of December marks mid-winter for the northern hemisphere, it marks mid-summer for the southern hemisphere. Due to this, people in the northern hemisphere experience winter solstice when people in the southern hemisphere are experiencing summer solstice.

The same works other way round when the Sun reaches its northern extreme in June, i.e. people in the northern hemisphere experience summer solstice, while people in the southern hemisphere experience winter solstice.

When the Sun is exactly at the equator, which happens twice in a calendar year, it is known as 'equinox' - i.e. 'vernal equinox' and 'autumnal equinox'.

Before you try to understand what solstice means, you need to understand that the term 'solstice' can be used (i) for the astronomical event in itself or (ii) for the day on which this astronomical event actually takes place.

As far as the astronomical event is concerned, it takes place twice in a year - first when the Sun is at its northernmost extreme at 23.5°North latitude and second when it is at its southernmost extreme at 23.5°South latitude.

When the Sun is at its northernmost extreme (23.5°N) the solstice is referred to as 'northern solstice', and when it is at its southernmost extreme (23.5°S) it is referred to as 'southern solstice'.

So the general terms for solstice are:

• Northern Solstice - which occurs when the Sun is at its northernmost extreme.
• Southern Solstice - which occurs when the Sun is at its southernmost extreme.

As this astral event occurs twice a year, it is also named on the basis of the month in which it occurs i.e.:
June Solstice - which occurs in the month of June (It is summer solstice for the northern hemisphere and winter solstice for the southern hemisphere.)

December Solstice - which occurs in the month of December (It is winter solstice for the northern hemisphere and summer solstice for the southern hemisphere.)

As the two hemispheres experience the two seasons - summer and winter, at different times of the year, the term used for this celestial event differs in accordance to the region in which you reside. On the basis of season in which it occurs, this astral event is called:

Summer Solstice - which occurs in summer (It is June solstice for the northern hemisphere and December solstice for the southern hemisphere.)
Winter Solstice - which occurs in winter (It is December solstice for the northern hemisphere and June solstice for the southern hemisphere)

As most of the Earth's land surface falls in the northern hemisphere (and it is home to 90 percent of the world population), the term 'Winter Solstice' is mostly used in reference to December solstice wherein the northern hemisphere experiences winter.

The solstice which occurs when the Earth's axis is tilted away from the Sun is referred to as the winter solstice. If you reside in the northern hemisphere, your region will experience winter solstice on 21st or 22nd of December. (On rare occasion though, it can even occur on 20th or 23rd December.)

On the other hand, If you reside in the southern hemisphere, your region will experience it on 20th or 21st June. (On rare occasion, it may even occur on 19th or 22nd December.)

Basically, winter solstice marks gradual shortening of nights and lengthening of days in the northern hemisphere, which continues till the next summer solstice in June - which happens to be the longest day of the year in this part of the world.

While most of the world celebrates Christmas in winter, Australia and other countries in southern hemisphere celebrate it in summer. To sum it up, the December solstice - wherein the Sun is at its southern limit, is the winter solstice in the northern hemisphere and summer solstice in the southern hemisphere.

Similarly, June solstice - wherein the Sun is at it northern limit, is the summer solstice for the northern hemisphere and winter solstice for the southern hemisphere.

When the Sun is at its southern extreme, all the areas beyond 66.5°N latitude are subjected to 24 hours of darkness, and all the areas below 66.5°S latitude are subjected to 24 hours of daylight, on this very day.

The fact that the winter solstice date in the northern hemisphere fluctuates between 20th and 23rd December as per the Gregorian calendar can make it a bit difficult for a layman to figure out the exact date when this astronomical event will occur.

In the year 2020, the solar solstice will be on 20th June (21:43 UTC) and on 21st December (10:02 UTC).

The importance of this occurrence is not merely restricted to astronomy. Irrespective of whether it is referred to as December solstice or winter solstice, you can't ignore the fact that this astronomical phenomenon, along with equinoxes - when the Sun is positioned at the Equator, has immense importance in various cultures across the world.

In some regions it marks the beginning of the season, and in some it marks the midpoint of the seasons. Even today winter solstice celebrations mean celebrating feasts and festivals, having bonfires and spending time with their loved ones, for scores of people across the globe.