Exoplanet Transit Lab: Using Real Kepler Data to Build an Evidence-Based Explanation

Students will explain how a planet crossing its host star can produce a temporary decrease in measured stellar brightness. They will interpret a light curve, estimate an orbital period from recurring events, and explain how phase folding displays observations according to their position within a trial orbit.

Students will also relate fractional transit depth to an approximate planet-to-star radius ratio under simplifying assumptions, recognizing how stellar brightness variations across the disk, transit geometry, contaminating light, and sampling affect that interpretation.

Students will develop and revise an explanation using quantitative observations, distinguish measurements from interpretations, and identify alternative explanations for an observed pattern. They will document their calculations so another learner can follow their reasoning.

Students will distinguish a consistency check using existing observations from independent confirmation, identify assumptions and limitations, and propose an additional observation that could help discriminate between competing explanations. They will compare their conclusions with published research while recognizing the different roles of classroom analysis and the original scientific investigation.

This activity is intended for high school students aged approximately 14 and older, introductory college astronomy or physical science students, and informal learners. Allow approximately 30–45 minutes, with additional time for spreadsheet or Python extensions.

Suggested formats include individual work, pairs, or small groups followed by a class discussion. In larger classes, an instructor could project the interface while students record predictions and calculations individually. The activity would fit after an introduction to light curves, orbital motion, or the evaluation of scientific evidence.

Students need subtraction, division, percentages, basic graph interpretation, and a calculator with a square-root function. The interactive version requires an internet-connected browser with JavaScript enabled. Printed plots support an offline version. No telescope, specialist laboratory equipment, account, or programming experience is required.

The complete activity and teaching materials are available at:
https://darksciencedocs.com/light-lab/exoplanet-transits/

Students begin by examining the full brightness record and writing an initial explanation for its recurring dips. They then inspect individual events, compare their timing, and calculate a period by dividing elapsed time by the number of intervening orbital intervals.

Using the stacking controls, students compare how different trial periods arrange the observations. They explain what changes in the display and what remains fixed, then examine a transit-depth estimate and its assumptions. To conclude, students write an evidence-based claim, consider an alternative explanation, and identify a useful follow-up observation before comparing their conclusions with the published interpretation.

The linked page provides the interactive interface, instructions, worked calculations, sources, and equivalent text descriptions and tables. Its four-page PDF contains the learner worksheet and educator answers. Downloadable observations support spreadsheet work, while an optional verification kit supports reproducibility and Python extensions.

The linked materials retain the reuse permissions stated on their website.

Make the reasoning process explicit by asking students to separate three statements: what they observe, what they infer, and what evidence would strengthen or challenge their inference. Collect initial predictions before students open the published interpretation, then revisit those predictions during the final discussion.

A useful timing check is to ask students how many gaps lie between fourteen consecutive events. There are thirteen intervals, so dividing elapsed time by fourteen would introduce a counting error. Encourage students to explain their denominator before calculating.

When discussing phase folding, ask students to trace one observation through different trial periods. Its measured brightness remains fixed while its horizontal position changes. This helps distinguish rearranging observations from collecting new evidence. A successful alignment should prompt discussion of consistency, rather than an automatic declaration of discovery.

For the depth calculation, have students identify the baseline, convert percentages to fractions, and state the assumptions behind the square-root relationship. Ask what additional information would be needed to report an absolute planetary radius.

Close by discussing how a stellar companion or blended source might mimic a planetary signal. Students should explain which follow-up measurements could test their alternative, and how those measurements would add information beyond the light curve.

Use the worksheet, calculations, and a short concluding explanation as formative assessment. Suggested criteria are whether students count orbital intervals correctly, calculate a reasonable period, interpret the phase-folded display, and identify assumptions behind the radius-ratio approximation.

For the scientific reasoning component, ask each student to submit a claim supported by two quantitative observations, one limitation, one alternative explanation, and one proposed follow-up observation. Assess whether the evidence supports the stated claim and whether the follow-up could distinguish competing explanations.

An exit question can ask: "What did rearranging the observations help you test, and what would require a new measurement?" A successful response distinguishes checking the existing pattern from obtaining independent confirmation.

Use the educator answers to diagnose misconceptions and guide revision. These are suggested assessment practices; no validated assessment instrument or measured learning gains are claimed.

Dark Science Docs / The Last Transmission. Exoplanet Transit Lab.
https://darksciencedocs.com/light-lab/exoplanet-transits/
The complete activity, worksheet, educator notes, observations, processing documentation, worked examples, and optional verification tools.

O'Donovan, F. T., et al. (2006). "TrES-2: The First Transiting Planet in the Kepler Field." The Astrophysical Journal Letters, 651, L61–L64.
https://arxiv.org/abs/astro-ph/0609335
The discovery paper provides the published orbital period and describes the photometric, spectroscopic, and radial-velocity evidence supporting the planet interpretation.

Thompson, S. E., Fraquelli, D., van Cleve, J. E., and Caldwell, D. A. (2016). Kepler Archive Manual. Space Telescope Science Institute.
https://archive.stsci.edu/kepler/manuals/archive_manual.pdf
Technical documentation explaining Kepler archive products, time conventions, light-curve columns, and quality information.