A Little Solstice Math

Quote of the Day

The question really isn't whether it's right, the question is can it be useful to people so they can understand the world around them and make better decisions.

— Milton Friedman on conceptual frameworks and theories. The longer I work in the technology field, the more I realize that creating a decision-making framework is a critical, but often overlooked part of problem solving.

Figure 1: Earth-Sun Orientation During Equinoxs and Solstices

Figure 1: Earth-Sun Orientation During Equinoxes and Solstices (Source).

We just went through the winter solstice of 2015, which in Minnesota is a subject of celebration. This means that we will now start to see more daylight.

The time of the winter solstice varies each year. It occurs on either 21-Dec or 22-December. One of the engineers in my group asked how the time of the winter solstice moves year-over-year. My response was that it moves forward ~six hours each year until a leap year happens, which resets the cycle.

A little calculation is often the best teaching example, so I put together the following table. In this table, I have the time of the solstices since 1980 to 2020, and computed the time increment from year-to-year. This table does a decent job of showing that the solstice times do increment by a bit less than six hours each year. I did my calculations assuming UTC. In Minnesota, we would normally use Central Time.

Figure 2: Table of Winter Solstices And Yearly Time-Shifts.

Figure 2: Table of Winter Solstices And Yearly Time-Shifts.

As you can see in Figure 2, the yearly time shift averages 5 hours and 48 minutes. In Figure 2, you can also see that a calendar year has ~365.242 days in it.


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