January days grow brighter as the Earth orbits the sun and leaves behind the Winter Solstice (December 21). That marked the annual day with the least amount of sunlight in the Northern Hemisphere–the Winter Solstice and the start of winter.
On March 20th, daylight and dark will be of equal length. This date is known as the Vernal Equinox, which marks the beginning of spring in the Northern Hemisphere.
The cause of the four seasons (marked by the Winter and Summer Solstices and the Vernal and Autumnal Equinoxes) is that the Earth’s axis of rotation is not perpendicular to its orbital plane of the solar system. Instead, its current angle of rotation is about 23.44 degrees.
As a consequence, for half the year (from around 21st of June to the 21st of December) the Northern Hemisphere is tilted away from the Sun. The resulting decrease in sunlight and temperature causes the seasons of fall and winter. Simultaneously, the Southern Hemisphere is tilted toward the Sun with increasing daylight and temperatures. The time when both hemispheres have equal exposure to the Sun and therefore equal daylight mark the spring and autumn equinox, approximately on March 21 and September 21 each year.
Many ancient civilizations connected solstices with religious celebrations and built temples and monuments that included techniques to measure these solar events. The Druid civilization of England built one of these world renowned monuments called Stonehenge.
Traditional Research Activity
Assign students to write a report of at least 100 words (or a PowerPoint presentation of at least five slides) that cites at least three resources.
Students should use the search terms listed in the pathfinder below to ensure relevance and save time. Students should address at least three of the following essential questions for critical thinking in their reports (you can substitute others):
- What are the summer and winter solstices and what causes them?
- How do the solstices mark the seasons of the year?
- How and why are the seasons different in the U.S. and in Australia?
- What are some religious celebrations related to the solstices?
Type Solstice OR Season in the search box.