Tag Archives: Solstice

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.

Sagittarius (The archer)

Constellation SagittariusSagittarius, the archer, is a zodiacal constellation that is rather easily found because of its distinctive teapot asterism. It is one of the 48 constellations cataloged by the 2nd century astronomer Ptolemy. It is located on the ecliptic between Scorpius and Capricornus. It can also be found by starting at Altair (a Summer Triangle star) and tracing southward along Aquila’s long axis. As is situated on southern most point of the ecliptic, this constellation hangs low in the southern sky, reaching its highest nightfall ascension in August. The Sun’s arrival at the southernmost point of the ecliptic around December 21st marks Winter Solstice and the first day of Winter.

This constellation has the distinction of presenting the foreground stars in the direction of the dense center of the Milky Way galaxy, which is rich in Messier objects. As such, it is worth taking the time to scan this constellation with binoculars or a small telescope. Several well-known nebula can be found in Sagittarius to include the Lagoon Nebula (M8), the Horseshoe Nebula, the Omega Nebula (M17), the Trifid Nebula (M20), and the Small Sagittarius Star Cloud (M24). Other Messier objects include M18, M22, M23, M25, M28, M54, M55, M69, M70 and M75.

IAU Sagittarius chart, Sky & Telescope magazine, June 5, 2011.
IAU Sagittarius chart, Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.

© James R. Johnson, 2014.

Gemini (The twins)

Constellation GeminiGemini, the twins, is a zodiacal constellation that was also one of the 48 constellations cataloged by 2nd century astronomer Ptolemy that remain among the 88 modern constellations. This constellation located above Orion’s left shoulder, and between Taurus and Cancer on the ecliptic. It is highest in the sky at nightfall in March, and is quickly identified by two rather bright stars of approximately equal brightness, Castor and Pollux, that represent each of the Gemini twins. The ecliptic reaches its northernmost separation from the celestial equator in Gemini, and the Sun’s arrival at this point marks the Summer Solstice.  The annual Geminids is a prominent annual meteor shower that peaks between December 13th and 14th. Only one Messier object, M35, is located in Gemini.

IAU Gemini chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.
IAU Gemini chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.

© James R. Johnson, 2014.