Early this year I started a new series on this blog titled "What Is". Thus far the focus is on the field of astronomy where we hear all sorts of cool science taking place in space. The goal of this series is to explain the details of different objects we hear about relatively frequently. It's been a couple of months since I last posted in this series, so it's time to pick things back up.
What is the Winter Solstice?
The last post in this series took a look at the summer solstice, but what is the winter solstice? Well, the winter solstice is basically the opposite of the summer solstice. If the Sun's rays are most direct on Earth's northern hemisphere on the summer solstice, than they are the least direct on the Earth's northern hemisphere on the winter solstice. Or another way to put it is to say that the Sun's rays are most direct on the SOUTHERN hemisphere on the winter solstice.
What causes this? The reason we have the summer/winter solstice, and the spring/fall equinox, is due to Earth's tilt of about 23.5 degrees. Because Earth is titled with an axis always pointing in the same direction, the angle the Sun's light hits the Earth changes.
The next winter solstice occurs on December 21, 2019. Although the winter solstice is usually on December 21, it can shift to December 20 or 22 depending on the exact time it takes place. On the winter solstice, the Sun is at its lowest point in the the northern hemisphere (or highest point in the southern hemisphere).
In the last post in this series on the summer solstice I noted that this was not typically the hottest day of the year because it takes time for land and water to warm up. This is similar for the winter solstice. The winter solstice is not the coldest time of the year even though the northern hemisphere is receiving less energy from the Sun than on any other day. Why? It's the opposite of the summer solstice. It takes time for the land and water to release energy and cool down. Thus January and February are typically colder than December in the northern hemisphere.
We are now done with the two solstices, but up next are the equinoxes!
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