Last updated: September 24, 2024
Lesson Plan
Optical Illusions and Mirage on the Great Plains
Is that really water?
NPS/D. Ocheltree
- Grade Level:
- Upper Elementary: Third Grade through Fifth Grade
- Subject:
- Science,Social Studies
- Lesson Duration:
- 60 Minutes
- Common Core Standards:
- 3.L.4, 3.L.4.a, 4.L.4, 4.L.4.a, 5.L.4, 5.L.4.a, 3.RF.4.c, 4.RF.4.c, 5.RF.4.c, 3.RI.1, 3.RI.2, 3.RI.3, 4.RI.1, 4.RI.3, 5.RI.3, 3.SL.1, 3.SL.1.d, 3.SL.2, 4.SL.1, 4.SL.1.d, 5.SL.1, 5.SL.1.d, 5.SL.2
- State Standards:
- 4th Physical Science 1.6 An object can be seen when light reflected from its surface enters the eyes. 4th History 1.1.a. Draw inferences about Colorado history from primary sources such as journals, diaries, maps, treaties, oral histories, etc.
- Thinking Skills:
- Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words.
Essential Question
• Name at least one environmental condition that must be present for a mirage to occur.
• Why were mirages dangerous to caravans on the Santa Fe Trail?
Objective
Explain the scientific mechanism behind mirages and identify their historic presence and impact along the Great Plains during the fur trade era.
Background
Overview Background: The southeastern Colorado trading post known as Bent’s Fort was established in 1833 along the Arkansas River bordering Mexico. As a major stop between Independence, MO and Santa Fe, NM, Bent’s Fort was a multicultural and international commerce hub on the Santa Fe Trail. Built on the homelands of the Cheyenne and Arapaho, deemed unorganized U.S. territory during this period, Bent's Fort traded primarily in buffalo robes procured by the Cheyenne and Arapaho people. Traders and merchants from dozens of other Native American nations and Mexico successfully supplied, traded, and exported items here until 1849.
The lessons in this unit are based on and include excerpts taken directly from Josiah Gregg’s 1844 published journal titled The Commerce of the Prairies. As a young man, Josiah first embarked with a caravan on the Santa Fe Trail in 1831. For the next nine years, he detailed the commerce, cultures, customs, ecology, and politics of the time. His insights detail firsthand experiences across the southern Great Plains during the fur trade era giving us a fuller picture of the lives and livelihoods for people at Bent's Fort.
The unit overview is as follows:
Lesson 1 – Geography of the Plains – Navigation Tools and Isolation
Lesson 2 – Riverways – Sustenance and Safety
Lesson 3 – Optical Illusions and Mirage
Lesson 4 – Climate, Drought and Seasons
Lesson 5 – Flora on the Plains – Grasses, Trees, and Agriculture
Lesson 6 – Fauna: Draft Animals, Buffalo and Rattlesnakes
Lesson 7 – Culture: Languages, Food, and Stereotyping
Lesson Background: There are times when data gathered from the senses can't be trusted. Under certain conditions light from the sun is bent to produce the illusion of water in the distance. During the 1830s and 1840s, traders in route like Josiah Gregg were susceptible to mistaking this visual phenomenon for actual water. In this Iesson students will view examples of optical illusions and examine the process of light refraction as a basis for understanding historic accounts of mirage and the potential risks involved.
Prior knowledge of the fur trade era will help give this lesson context. See "Introduction to Bent's Old Fort PowerPoint" in lesson materials.
Preparation
Materials:
- hard copy prints of optical illusions or online examples
- Josiah Gregg Lesson 3 narrative text
- exit ticket
Materials
This is the companion text for Lesson 3. Josiah Gregg writes about his experience with optical illusions and mirages along the Santa Fe Trail in the 1830s.
Download Josiah Gregg Unit Lesson 3 Optical Illusions and Mirage narrative text
Photo of mirage on two lane road
An optional 37-slide introduction to Bent's Old Fort with notes to build prior knowledge of the fur trade era before teaching this lesson.
Download Introduction to Bent's Old Fort PowerPoint
Lesson Hook/Preview
Present several examples of optical illusions either in print or screen form and ask learners to write down what they see without sharing it with a peer. Possible resource: 32 optical illusions and why they trick your brain | Live Science (Accessed August 14, 2024.)
Procedure
1. Pair or group students together to view optical illusion examples and compare what they saw with their peers.
2. As a whole group, ask volunteers to share their observations.Choose a few examples to explain how the illusion is produced.
3. Forming back into pairs or groups, provide 2-3 minutes to discuss the following question: "What optical illusions might travelers on the Santa Fe Trail in the 1830s have experienced and what might have caused them?" Check in with groups as they brainstorm and provide feedback.
4. Assign reading of Josiah Gregg’s “Optical Illusions and Mirages” narrative text.
5. After reading, view scientific explanation of mirages video titled Why Does It Look Like There's Water On The Road? (youtube.com) (Accessed August 14, 2024). Summarize video explanation of refraction after viewing.
6. Contextualize isolation on the Great Plains during the fur trade era with the experience of optical illusions and mirages. Contrast the survival risks involved both then and now considering population distribution, technology available, accessible water, travel options, etc.
7. Give pairs or groups 2 minutes to review the scientific conditions that cause a mirage.
8. Conclude by reclarifying the process of refraction in a desert or highway situation.
9. Pass out Exit Ticket.
Vocabulary
illusion - a thing that is wrongly perceived or interpreted by the senses
mirage - an optical illusion caused by the refraction of the sun's light by heated air
density - mass per unit volume or the amount of matter in a given space
reflection - the return of light or sound waves from a surface
refraction - the bending of light waves when passing through substances of different densities
Assessment Materials
Josiah Gregg Unit Lesson 3 Exit TicketExit ticket containing lesson 3's essential questions.
- Name at least one environmental condition that must be present for an optical illusion to occur.
- Why were mirages dangerous to caravans on the Santa Fe Trail?
Exit ticket containing lesson 3's essential questions.
Rubric/Answer Key
Josiah Gregg Unit Lesson 3 Exit TicketAnswers to Josiah Gregg Unit Lesson 3 Exit Ticket questions
- Name at least one environmental condition that must be present for an optical illusion to occur. Possible answers include: Light traveling through substances of differing temperature and density will cause it to bend or refract which distorts the image making dry land appear as water.
- Why were mirages dangerous to caravans on the Santa Fe Trail? Due to the lack of available water for hundreds of miles along the Santa Fe Trail, dehydrated merchants could be mislead and run off course presuming they were headed toward lifesaving water for themselves and their animals.
Supports for Struggling Learners
Pair visually impaired students with a partner/support staff who can supply detailed descriptions of optical illusion examples. Alternatively, provide visually impaired students with a range of tactile objects which feel similar but are not made of the same substance. Change the "normal" condition of one object by adding a solution to it which it does not usually have - like lotion or oil.
Enrichment Activities
Science extension: Draw a diagram of light reflection (as with a mirror or lake) and light refraction (as with a mirage or rainbow).
Language extension: Consider how people might have explained a mirage before they knew the scientific principle behind it. Write a mythological story to explain mirages.
Additional Resources
A digitized version of the 1849 original two volume publication by Josiah Gregg is accessible here:
Commerce Of The Prairies (1849) Josiah Gregg : Victorian Vault : Free Download, Borrow, and Streaming : Internet Archive (Accessed August 14, 2024)
Santa Fe National Historic Trail (U.S. National Park Service) (nps.gov)
Related Lessons or Education Materials
As a young man, Josiah Gregg embarked with a caravan on the Santa Fe Trail in 1831. For the next nine years, he kept a journal detailing the commerce, cultures, customs, ecology, and politics of the time making eight trips along this trading route. His journal titled The Commerce of the Prairies was published in 1844. All lessons in this unit are based on and include excerpts directly from this text. The unit overview is as follows:
Lesson 1 – Geography of the Plains – Navigation Tools and Isolation
Lesson 2 – Riverways – Sustenance and Safety
Lesson 3 – Optical Illusions and Mirage
Lesson 4 – Climate, Drought and Seasons
Lesson 5 – Flora on the Plains – Grasses, Trees, and Agriculture
Lesson 6 – Fauna: Draft Animals, Buffalo and Rattlesnakes
Lesson 7 – Culture: Languages, Food, and Stereotyping