This video explains that the gradual change in the direction of Earth's axis causes perihelion (the point when the Earth is closest to the Sun) to occur at different times in the calendar year.
Students will learn that the winter solstice always occurs on the same date because our calendar is based on the direction of the Earth's tilt with regard to the Sun.
Teaching Tips
Positives
This video takes a unique approach as it starts with a misconception then shows why it is incorrect.
There is a season simulator available to view the Earth throughout the seasons.
Additional Prerequisites
This video is one of a series of Khan Academy videos on Earth's rotation and tilt. Students should watch the video on precession and obliquity before watching this video.
Differentiation
Earth science classes could work in groups to act out the concept of precession. If students need help getting started, teachers could assign parts (e.g., narrator, sun, earth, perihelion, aphelion). Kinesthetic learners will enjoy this activity.
Other resources on this topic include this video that explains how seasons work, this Khan Academy video on how Earth's tilt causes the seasons, and this lesson on how latitude affects the climate.
Scientist Notes
This resource video is used to clarify some of the more confusing aspects of precession, specifically in regards to the changing of when our seasons occur. Precession will not cause a calendar change to when our seasons occur. This resource is recommended for teaching.
Standards
Next Generation Science Standards (NGSS)
ESS1: Earth's Place in the Universe
HS-ESS1-4 Use mathematical or computational representations to predict the motion of orbiting objects in the solar system.
ESS2: Earth's Systems
HS-ESS2-4 Use a model to describe how variations in the flow of energy into and out of Earth’s systems result in changes in climate.
Common Core English Language Arts Standards (CCSS.ELA)
Speaking & Listening (K-12)
CCSS.ELA-LITERACY.SL.11-12.2 Integrate multiple sources of information presented in diverse formats and media (e.g., visually, quantitatively, orally) in order to make informed decisions and solve problems, evaluating the credibility and accuracy of each source and noting any discrepancies among the data.
