Lesson 4: Evidence for the Expanding Universe

How do astronomers know the universe is expanding?

What is redshift, and how does it provide evidence of galaxy motion?

How does Hubble’s Law relate the distance of galaxies to their velocity?

What patterns in galaxy motion help scientists understand the history and growth of the universe?

How can we use observational data to support explanations about cosmic expansion?

Redshift

Blueshift

Hubble’s Law

Galaxy

Recessional velocity

Light spectra

Expansion of the universe

Astronomical observation

HS-ESS1-2 – Construct an explanation of the Big Bang theory based on astronomical evidence, including redshift measurements and motion of distant galaxies.

NGSS Crosscutting Concepts

Cause and Effect

Systems and System Models

Stability and Change

Patterns

Students will analyze real astronomical data (galaxy redshifts and velocities) to support scientific explanations.

Students will practice interpreting graphs, scatterplots, and tables to identify patterns in observational data.

Students will construct evidence-based explanations linking observational data to scientific models of the universe.

Students will investigate how galaxies move and how their light provides evidence of cosmic expansion. Using redshift data and simplified galaxy velocity/distance charts, students will interpret patterns that support Hubble’s Law and the expansion of the universe.

Activities may include plotting galaxy velocities versus distances, simulating expanding space using physical models, or analyzing spectra from distant galaxies.

Purpose: Reinforce understanding of observational evidence, scientific reasoning, and data interpretation in cosmology.
DOK Level: 3 – Strategic Thinking / Reasoning (analyzing data to construct scientific explanations)

Students can relate redshift and cosmic expansion to modern space exploration, telescope observations, and images from missions like Hubble Space Telescope. Understanding galaxy motion connects to broader questions about humanity’s place in the universe and ongoing international efforts in astronomy research.

Students may think galaxies are moving through space like projectiles rather than space itself expanding.

Students may confuse redshift and blueshift with Doppler effect in everyday sounds without connecting it to light.

Students may believe that all galaxies are moving away from Earth specifically, instead of understanding that space itself is expanding.

Students may struggle to interpret data in graphs or spectra to draw scientific conclusions.

Scaffolded instruction for reading and plotting redshift and velocity data.

Graphic organizers to visualize the relationship between galaxy distance and velocity.

Use of simulations to model expansion of space for visual and hands-on learners.

Peer collaboration for data analysis and discussion of patterns.

Clear rubrics and step-by-step guides for plotting and interpreting galaxy data.

Support for interpreting spectra, graphs, and observational datasets.

• Checkpoints during galaxy data analysis and plotting exercises.

• Quizzes on key vocabulary and concepts (redshift, Hubble’s Law, galaxy motion).

• Evaluation of student-created graphs comparing galaxy distance and velocity.

• Constructed-response assignments asking students to explain how redshift data supports the expanding universe.

• Astronomy slides and worksheets on Hubble’s Law

• Galaxy velocity and distance datasets (simplified for classroom use)

• Online simulations of expanding space and galaxy motion

• Spectral images from distant galaxies (NASA, ESA, or classroom datasets)

• Articles or case studies demonstrating the history of Hubble’s observations