Today – December 22 – is the winter solstice. It is the “shortest” day of the year, except it has 24 hours in it just like every other day. When we say it’s the shortest day of the year, we really mean that it is the day with the shortest period of sunlight.
The reason this happens is because Earth rotates on an angle and therefore different sections of the planet are exposed to different amounts of sunlight, depending on where the planet is in its orbit.
Other than being annoying, it would seem that losing a bit of sunshine is not that big of a deal. Except that it can be a big deal. Losing just a bit of sunshine can have rippling effects, especially to those organisms that are photosynthetic (that process sunlight to live).
One obvious example of this is what is known as Seasonal Affective Disorder (SAD). This disorder is a mood-altering condition believed to result from a reduced exposure to sunlight. Less sunlight causes many people’s moods to lower, sometimes to the point where it can be debilitating. Our levels of serotonin are directly affected by our exposure to the sun’s light. Since serotonin is a neurotransmitter that is implicated in maintaining our mood, less serotonin means less happiness. This is further evidenced by the fact the most common type of antidepressant is geared at increasing serotonin levels.
Our exposure to levels of light can also affect our sleep patterns. Certain glands in our brain regulate the release of melatonin, a hormone which determines our sleep patterns. However, during daylight hours, our eyes relay information to our brain that essentially says, “don’t produce melatonin.” At night, when it’s dark, melatonin production increases and we feel tired.
If you find yourself feeling more tired than usual during periods of reduced daylight, it might not be your imagination. Increased melatonin production coupled with the energy spent on fighting cold weather naturally leads to people being more tired during the winter months.
So, while a temporary reduction in daylight should not cause any catastrophic issues for most people, it is worth celebrating that our days will slowly get “longer” and that more daylight is on its way.