Lesson 4: Evidence for the Expanding Universe

-How do astronomers determine that the universe is expanding?

-How does redshift provide evidence for galaxy motion and expansion of space?

-What patterns exist between galaxy distance and recessional velocity?

-How does Hubble’s Law support the Big Bang model?

-How can mathematical relationships and observational data be used together to explain cosmic expansion?

-Why is the expansion of the universe considered one of the strongest pieces of evidence in cosmology?

Hubble’s Law

Redshift

Blueshift

Galaxy

Recessional velocity

Expansion of space

Light spectra

Distance

Velocity

Slope

Correlation

Astronomical observation

HS-ESS1-2 – Construct explanations of the Big Bang theory using astronomical evidence including redshift measurements and galaxy motion

HS-PS4-3 – Analyze how electromagnetic radiation provides evidence about the structure and behavior of the universe

NGSS Crosscutting Concepts

-Cause and Effect

-Patterns

-Systems and System Models

-Scale, Proportion, and Quantity

-Stability and Change

Students will interpret scatterplots, graphs, and spectral data to identify mathematical relationships in scientific datasets.

Students will analyze proportional relationships between variables and evaluate evidence supporting scientific models.

Students will construct evidence-based explanations integrating mathematical reasoning with observational astronomy data.

Students will investigate how astronomers use galaxy motion and redshift data to determine that the universe is expanding. Using authentic-style datasets, students will graph galaxy distance versus recessional velocity and identify the linear relationship described by Hubble’s Law.

Students will analyze how patterns in observational data support large-scale cosmological models and evaluate how multiple lines of evidence strengthen scientific explanations.

Activities may include:

-Graphing galaxy velocity versus distance to identify Hubble’s relationship

-Analyzing spectral shifts to determine relative galaxy motion

-Using simulations to model expansion of space over time

-Comparing different cosmological models using observational evidence

-Evaluating how slope in a graph relates to expansion rate

Purpose: Reinforce quantitative reasoning and evidence-based scientific explanation by connecting mathematical relationships to models of cosmic expansion.

DOK Level: 3–4 (Strategic Thinking to Extended Reasoning)

Students connect Hubble’s discoveries to modern astronomy research, telescope technology, and ongoing studies of the universe using observatories around the world.

Students also examine how mathematical models are used in many scientific fields to identify patterns and make predictions about systems too large or distant to observe directly.

Connections can be made to current space missions and advancements in imaging technology that continue to refine cosmological understanding.

Students may think galaxies are moving away from a central point in space rather than understanding expansion of space itself.

Students may confuse redshift with changes in visible color rather than wavelength stretching.

Students may assume Hubble’s Law proves the Big Bang independently rather than serving as supporting evidence.

Students may struggle to distinguish between correlation in data and interpretation of causation.

Students may misunderstand the scale of distances and velocities involved in cosmology.

-Step-by-step graphing supports for velocity-distance relationships

-Color-coded spectral line analysis activities

-Interactive simulations of cosmic expansion and galaxy motion

-Scaffolded CER writing focused on data interpretation

-Tiered datasets with varying complexity levels

-Peer collaboration for graph analysis and evidence evaluation

-Visual supports connecting mathematical slope to expansion rate

-Graphing analysis of galaxy distance versus recessional velocity

-Interpretation of galaxy spectra showing redshift patterns

-Quiz on Hubble’s Law, redshift, and cosmic expansion concepts

-CER response explaining how observational evidence supports the expanding universe model

-Formative checkpoints during graphing and spectral analysis activities

-Evaluation of student-created models explaining expansion trends

Galaxy velocity and distance datasets

Spectral line images and redshift examples

Graphing tools or digital graphing software

Simulations of Hubble expansion and galaxy motion

NASA/ESA astronomy datasets and visuals

Worksheets on Hubble’s Law and proportional relationships

Articles or case studies on Edwin Hubble’s observations and discoveries