Tag Archives: sunset

An Interesting Astronomical Observation Project

Most people intuitively know that days are shorter and nights are longer during the winter months, and days are longer and nights are shorter during the summer months. For those people who don’t know why, but would like to develop an understanding of why that is, here is an interesting observation project that begins to tease out the answer.

As I write this on December 23, 2019, we are just two days past the winter solstice, or the astronomical first day of winter. This event coincides with the shortest day and longest night of the year. And, at around this time, the sun rises and sets at its southernmost point on the horizon. This is a great time to begin the project, and observe the rise and set points move northward over the next six months.

This project can work with observing just sunrises, just sunsets, or both. After deciding when events you can observe, the first thing to do is select one or two observation points that are readily and repeatedly available. One should be toward the east in the mornings for sunrises, and the other toward the west in the afternoons for sunsets.

For the most casual observer, make a mental note of the sunrise or sunset point of the horizon, and the time. This first observation is your baseline. Make this observation every couple of days, and compare them with your baseline observation. During the period between the winter solstice (around December 21st) to the summer solstice (around June 21st), an observer should note that the rise or set point moves northward as the winter and spring progress. The sunrise time should be earlier and the sunset time should be later during this progression. By the time you get to June, you’ll be surprised at how much the rise or set points have moved, and how much the time has changed as well. From June 21st back to December 21st, the rise or set point should be moving southward on the horizon while the rise time gets later and the set time gets earlier.

More sophisticated observers can use a compass to record the azimuth of the sunrise or sunset, and record their observations in a spreadsheet for later analysis. A magnetic compass that can read degrees or a smartphone app can do the job. If you’ve never used a compass, they are not difficult to learn, and there are many online resources. Also, be sure to record the time in Universal Coordinated Time (UTC) to eliminate any confusion that daylight savings time might impose.

As an example for us in the eastern time zone, to convert standard time (EST) to UTC, add five hours. To convert daylight savings time (EDT), add four hours. Be aware that from early May until mid-August, sunset times of 8 pm EDT (and later) will use the next days date. For instance, sunset at 8:36 pm on June 21st might be recorded as 2020-06-21 20:36 EDT. Converting this to UTC by adding four hours pushes the time past midnight, and results in 2020-06-22 00:36 UTC.

If anyone actually does the observations, and would like an interpretation of the results, I would be glad to work with you, or write more on this topic, just let me know.