The Winter Solstice

This past Sunday I started my ride exactly at 10:03am. I'll explain why in a couple of paragraphs but the short explanation is that I couldn't pass up mixing a bike ride with an astronomical event. 

The winter solstice occurs exactly when the sun is at it's lowest point in the sky and is directly over the Tropic of Capricorn. This is the moment the sun stops getting lower in the sky and starts its journey back towards the equator. The earth is tilted 23.5 degrees to it orbit and so the sun's elevation at noon appears to rise and fall (-23.5 to +23.5). That is why if you took a picture of the position of the sun at noon every day you would get a picture like the one below.

 

Its call the analemma and it looks a figure 8. The lowest point is the winter solstice and the highest point is the summer solstice. The middle of the figure 8 is where the spring and fall solstice occurs (when the sun is directly over the equator.)

This past Sunday (the day of the winter solstice) I had planned a ride starting at 10 am but when I saw that the time of the winter solstice was 10:03 am local time I changed my ride to start then. The exact day and time of the solstice changes because of perturbations in the earth's orbit which I won't go into detail explaining so it was just lucky happenstance that the winter solstice was almost exactly when I planned to start the ride. Laura was the first one to notice the unusual ride start time and because she could not attend so we sent her a picture to welcome her to the winter solstice.  

We sent it at exactly 10:03 am of course. The ride itself was fine for a winter ride. It was in the mid 40s so not too cold but it was a little windy at times. We did 33 miles which helped me reach my mileage goal for the year. I'm sure I'll do a few more rides in before the new year. 

I know it will be few more months before winter is over and the weather will be warmer but it is good to know the sun has started it trek back north and the days will now be getting longer.