Learning Objectives
- Model astronomical scale and measure parallax with uncertainty.
- Make measurements or classifications with explicit uncertainty.
- Separate direct evidence from model-dependent interpretation.
Preparation
- Review the parallax relation d(pc) = 1/p(arcsec) and the scale discussion in OpenStax Astronomy 2e.
- Bring a ruler or measuring tape if instructed.
Materials and Data
- Meter sticks or measuring tape
- Two observing positions separated by a measured baseline
- Nearby object and distant background markers
- Spreadsheet or calculator
Apparatus and Setup
- Set two observing stations at least 2.0 m apart and measure the baseline to the nearest centimeter.
- Place the nearby target 3-6 m from the baseline and background markers at least three times farther away.
- Provide a printed angular scale or require students to compute angle from lateral shift and background distance.
Procedure
- Measure a baseline between two observing positions in meters.
- From each baseline endpoint, record the apparent position of a nearby object against distant background markers.
- Measure or estimate the angular shift using a protractor, printed scale, or small-angle geometry supplied by the instructor.
- Repeat the measurement at least three times and compute the mean shift and range.
- Build a scale model in which 1 AU corresponds to a chosen classroom or campus distance, then place Earth, Mars, Jupiter, and Neptune on that scale.
Measurement Record
Use this structure or an equivalent table in your lab notebook.
| trial | baseline | apparent shift | angle | distance estimate | uncertainty source |
|---|---|---|---|---|---|
Analysis and Uncertainty
- Compute fractional uncertainty in the parallax measurement from repeated trials.
- Use proportional reasoning to explain why smaller parallax means larger distance.
- Compare the classroom parallax setup with stellar parallax and name two limitations of the model.
Deliverables
- Baseline and parallax measurement table
- Distance estimate with uncertainty
- Scale-model table
- Short comparison of classroom and stellar parallax
Assessment Criteria
- Correct measurement procedure
- Uncertainty estimate
- Correct inverse-distance reasoning
- Clear scale conversion
References, Software, and Data Provenance
- OpenStax Astronomy 2e, section 19.2
- OpenStax Fig. 19.6 Parallax
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.