Learning Objectives
- Interpret emission and absorption spectra and connect spectral features to composition and motion.
- Make measurements or classifications with explicit uncertainty.
- Separate direct evidence from model-dependent interpretation.
Preparation
- Read OpenStax Astronomy 2e sections 5.1-5.6 on light, spectra, spectral lines, and Doppler shifts.
Materials and Data
- Instructor-provided spectra or OpenStax spectral diagrams
- Known rest wavelengths for hydrogen lines
- Calculator or spreadsheet
Apparatus and Setup
- Provide three labeled data files or printed spectra: continuous, absorption-line, and emission-line examples.
- Provide a rest-wavelength table including H-alpha 656.3 nm, H-beta 486.1 nm, and at least one [O III] line.
- If using software, lock axes so students read wavelengths rather than pixel positions.
Procedure
- Classify three spectra as continuous, absorption-line, or emission-line and justify each classification from visual evidence.
- Identify at least two spectral lines in a provided spectrum using a rest-wavelength table.
- For one shifted line, measure observed wavelength and compute radial velocity using v/c = Delta lambda / lambda.
- Compare two spectra of the same object type and identify what changes could be due to temperature, composition, or motion.
- Record whether each inference is direct observation or model-dependent interpretation.
Measurement Record
Use this structure or an equivalent table in your lab notebook.
| spectrum | line ID | rest wavelength | observed wavelength | shift | velocity | interpretation |
|---|---|---|---|---|---|---|
Analysis and Uncertainty
- Show wavelength shift calculation with units.
- State whether the object is redshifted or blueshifted.
- Explain one reason why calibration matters before interpreting line positions.
Deliverables
- Annotated spectra
- Line-identification table
- Doppler calculation
- Short interpretation paragraph
Assessment Criteria
- Correct spectrum classification
- Correct line identification
- Dimensional calculation
- Evidence/inference distinction
References, Software, and Data Provenance
- OpenStax Astronomy 2e, sections 5.1-5.6
- OpenStax Fig. 5.21 Three Kinds of Spectra
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.