Twice a year Earth undergoes a celestial alignment called an equinox. There are another two similar events called solstice which occur in June and December. The equinox alignments occur in September, the Autumnal Equinox and spring, the Vernal Equinox. In just a few days, Wednesday, September 22, 2016 to be exact, we are going to experience the autumnal equinox. This is the day when the Sun passes directly over the Earth’s equator. This means that winter is officially on its way. For those of us in the northern hemisphere the longer days of summer are fading fast giving way to the longer nights on winter. All to soon the local meteorologist will be telling us about the chill index and the dreaded feels like 20° F outside. But I’m a big fan of the winter cold. So, good for me.
Okay, so there are a lot of misconceptions about the seasonal transition even though everybody has heard about it since they were kids. Many people seem to think that the changing seasons are due to the fact that Earth’s orbit around the Sun isn’t exactly a circle. Fact is, in the northern hemisphere where we experience winter in December, the Sun is actually closer to the Earth by a small amount and farther away in the summer.
It all has to do with the Earth’s axis. Earth’s axis is not straight up and down relative to the Sun. It’s titled 23.5 degrees. Now, as the Earth moves around the Sun, it maintains the 23.5-degree tilt. That means the light from the Sun doesn’t hit the entire surface of the Earth directly. Click on the simulation below to better understand this phenomenon.
Simulation downloaded from the Astronomy Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu). Used with permission.
As you can see, it has everything to do with the amount of light per square centimeter that’s falling on us, and not how close or far away from the Sun the Earth is in its orbit around the Sun.
So, if you’re like me and you enjoy the cooler crispier air that comes with fall and winter, then it’s time to come alive and get out there and do some stargazing. But bundle up “cause baby, it’s cold outside.”