Ah, the solstice-the first official day of winter, and the start of longer days. The word deriving from the Latin words for ‘sun’ and ‘to stand still’. This year, it fell upon December 21st, and unlike some time ago, no-one was worrying about the world’s supposed end. So really, what is this event?
To begin with, it is the shortest day only for those living in the Northern Hemisphere. For those living in the south, the effect is reversed, and therefore they recently had the summer solstice. As you may already know, the tilting of the Earth and its poles towards and away from the sun causes the seasons. Up here in the North, the winter solstice is brought on by the North Pole being tilted the furthest away from the sun that it will be in the year.
The opposite is true for the summer solstice. Despite any preconceptions you may have, this date is not the coldest day of the year because the Earth still retains a great amount of thermal mass retains heat from summer and fall and the cooling process is gradual. Therefore, these coldest days generally begin about a month after the solstice. As astronomer Robert Howell put it, “If you think about turning up an oven—it takes it a long time to heat up, and after you turn it off, it takes a while for it to cool down. It’s the same with the Earth.”
So is the Solstice on the same date every year? Well, no, because the timing depends on when the Earth is tilted the furthest away from the sun. In addition, there is a discrepancy between the human calendar year of 365 days and the astronomical rotation of our blue planet, which takes about 365.24 days. Thus, the solstice is usually around the 21st of December, and not always exactly on the date. The leap year system of adding an extra day to the calendar every four years may ensure that our calendars are accurate, however it fluctuates the actual date of the solstice, making the different dates a human change and not an astronomical one.
As the writer Albert Camus once said, “In the depth of winter, I finally learned that there was in me an invincible summer.”