Learning Objectives
- Classify galaxies with documented criteria and interpret simple redshift-distance evidence.
- Make measurements or classifications with explicit uncertainty.
- Separate direct evidence from model-dependent interpretation.
Preparation
- Read OpenStax Astronomy 2e sections on galaxy morphology, Hubble's law, and redshift interpretation.
Materials and Data
- Instructor-provided galaxy image set
- Classification rubric
- Small redshift-distance table
- Calculator or spreadsheet
Apparatus and Setup
- Provide a galaxy image set with source notes and a classification rubric.
- Provide a redshift-distance table with at least six galaxies, including one likely outlier.
- If spectra are used, provide rest and observed wavelengths for at least two lines.
Procedure
- Classify at least eight galaxies as spiral, elliptical, irregular, interacting/peculiar, or uncertain using the provided rubric.
- For each classification, cite at least two visible criteria such as arms, smoothness, color, dust, asymmetry, tidal features, or star-forming knots.
- Compute redshift for two provided spectral-line measurements or use a provided redshift table.
- Plot recession speed versus distance for a small sample and estimate the slope.
- Identify one outlier or source of scatter and propose a physical or measurement explanation.
Measurement Record
Use this structure or an equivalent table in your lab notebook.
| galaxy | morphology | criteria | redshift or velocity | distance | classification caveat |
|---|---|---|---|---|---|
Analysis and Uncertainty
- Distinguish morphology classification from evolutionary history.
- Compute or interpret Hubble-law slope with units.
- Explain why distance and redshift evidence must be calibrated before making cosmological claims.
Deliverables
- Galaxy classification table
- Annotated example image
- Redshift-distance plot
- Short interpretation of slope and scatter
Assessment Criteria
- Classification evidence
- Redshift/Hubble-law calculation
- Recognition of ambiguity
- Plot labels and units
References, Software, and Data Provenance
- OpenStax Astronomy 2e galaxy and cosmology chapters
- ESA/Hubble image pages or NASA/IPAC metadata as assigned
- NASA/IPAC Extragalactic Database for metadata verification when used
Any additional dataset, image, or software source used by an instructor should be added to ../reference-log.md with source, access date, license or usage note, and processing steps.