Io Saturnalia! Throw Some Shade! Use Science, Physics, and Culture to Teach the Solstice to Your Students

This Friday (December 21) marks the December solstice—the shortest day of the year in the Northern Hemisphere, and the longest day of the year in the Southern Hemisphere. The maximum difference in daylight between the June solstice and the December solstice is a whopping five hours and 50 minutes!

As schools wind down for holidays, take some time to introduce the solstice through Earth science, geography, and culture. Consult a list of key resources in our Teachers Toolkit.

Science of the Solstice

A solstice is an event in which a planet’s poles are most extremely inclined toward or away from the star it orbits. Here, the Southern Hemisphere gets the maximum intensity of the Sun’s rays during the December solstice.
Photograph by NASA and Robert Simmon, using data ©2010 EUMETSAT

A solstice is an event in which a planet’s poles are most extremely inclined toward or away from the star it orbits. At Nat Geo headquarters in Washington, D.C., the precise time of the December 2018 solstice—when solar declination hits the Tropic of Capricorn—is 5:23pm.

Teach the science of the solstice:

During the December solstice, the far north is dark blue, indicating that little sunlight is being reflected back into space. The most sunlight is being reflected out of the Southern Hemisphere, which is experiencing its summer solstice, the longest day of the year.
Images courtesy Takmeng Wong and the CERES Science Team at NASA Langley Research Center

Shadow Geography

Students trying to find the right positioning of Earth in their tabletop orbital plane.
Photograph by Jesse Lowes

The winter solstice is a shadowy subject. So throw some shade!

One of our Grosvenor Teacher Fellows, Jesse Lowes, offers a terrific lesson on shadow geography—or, how “if you know how to read it, a shadow can tell you the time, reveal which direction you’re traveling, help pinpoint your location on Earth, and even tell you where Earth is in orbit around the sun.”

Jesse’s class modeled Earth’s orbital path around the sun using polystyrene balls tilted at an earthly 23.5° angle. (Polystyrene balls are apparently indispensable for studies of solar shadows and the solstices.)

In Jesse’s example, students were able to deduce where he was in a photograph based on the positioning of his shadow. He encourages other educators to have students do some similar “shadow sleuthing” by collecting images containing shadows with all but one of the following variables identified: date, time, and location. (Google Earth is a great source for collecting these real-life images.) Have students predict the missing information using a sun-Earth shadow model and/or a shadow tracking website, such as Find My Shadow.

Io, Saturnalia and Stonehenge!

Saturnalia was a wild carnival including banquets, parties, and gaming, above.
Photograph by WolfgangRieger, courtesy Wikimedia. Public domain

Why would ancient Romans greet each other with a “yo, Saturnalia” in the week preceding the bleak midwinter? Saturnalia was a wild carnival that marked the final passage of autumn into winter. During Saturnalia festivities, Romans enjoyed banquets, gambling, jokes, gifts, and a tradition of usurping strict social structures.

Read through “The Culture of the Solstices” from our encyclopedic entry to introduce students to Saturnalia, then celebrate, yo! Here are some foods for a certified Saturnalian banquet:

Saturnalia is hardly the first celebration associated with the December solstice, of course. The sacred site of Stonehenge, for instance, was probably created at least in part to honor the solstices thousands of years before the Romans were celebrating. Its central “avenue” is aligned to the sunset of the December solstice, and, looking toward the famous circle, the December solstice sunset appears directly in front of the Heelstone. (Some archaeologists think this has more to do with geology than astronomy or ancient Britons, however. Use our study guide to learn more about that.)

Like the Romans, the ancient Britons of Stonehenge feasted during the solstice. Cater your winter party to their tastes:

  • Salisbury granola: hazelnuts, dried cherries, and berries
  • soft cheese plate with cottage cheese, yogurt, and butter
  • pork (ideally imported from Scotland)
  • apples, likely sweetened with honey
Looking toward the famous circle, the winter solstice sunset appears directly in front of the Heelstone.
Photograph courtesy The Stones of Stonehenge. CC-BY-NC-ND-4.0

To Sum Up the Solstice

Whether you’re planning a fresh approach to a winter feast, coming out of the shadows with model geography, or learning the reason for the seasons … don’t forget the solstice!


Nat Geo: What is a solstice?

Nat Geo: The Reason for the Seasons

Nat Geo: Solstice Solar Radiation

Nat Geo: Use ‘Shadow Geography’ to Find Your Place

Nat Geo: Parts of Stonehenge May Have Been In Place Long Before Humans

Judith Geary: A “Certified” Roman Banquet for Saturnalia

The Romans in Britain: Recipe for Gliris or Glis-Glis (Dormice)

Texas Classical Association: Recipe for Saturnalia Cake

Stephanie Dray: Io Saturnalia! A Holiday Party Tray, Ancient Roman Style

English Heritage: Food and Feasting at Stonehenge

Time and Date: Shortest Day of the Year in the Northern Hemisphere

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