Experiment · EN

Otherlight — Exoplanet Simulation

Exoplanet transits, exomoons and binary stars as interactive labs in the browser: change a planet's size or orbit and watch the light curve respond, follow a Guided Lab from hypothesis to interpretation, or run a validated radial-velocity model on your own machine.

simulationbrowser apptransitlight curvesexomoonsbinary stars

Overview

Otherlight is a free, open-source simulation app for exoplanet transits, exomoons, detached binary stars, photometry and timing. It runs in a browser tab, entirely on your own device: no account, no upload, no installation. It complements the hands-on experiments on this site: where the Transit Method experiment builds a light curve with a lamp and a ball, Otherlight lets you vary every parameter of the system and see the light curve, the geometry and the formula change together.


Target group	Bachelor's and master's level (STEM), educators
Method	Interactive simulation, Guided Labs
Platform	Web browser (desktop recommended); source code for a SwiftUI app for Apple platforms
Language	English
Licence	MIT (open source)
Status	Pre-release (alpha)

Open the app · Screenshot tour · Source code on GitHub

What you can do

Simulation: connect geometry to a light curve. Change the planet radius and watch the transit depth follow. The observer's view of the star, the relative-starlight curve and the depth formula δ ≈ (R_p / R_★)² stay in step, so the arithmetic is visible next to the picture. Two models, A and B, can be compared side by side, and the light curve can be exported as CSV.

Otherlight Education workspace: the star seen from the observer with two planet sizes, A and B, the relative-starlight curve with two transit dips, and the transit depth formula.

Guided Labs: from prediction to evidence. Lessons advance one phase at a time — hypothesis, experiment, interpretation. The prompt, the evidence and the learner's written answers stay together, a session can be saved as a workspace file and resumed later, and a lesson report can be downloaded.

Guided Lab: a worked example for a central transit, with phase navigation and the lesson report download.

Scientific workspace: keep the boundary explicit. A separate, strictly validated Newtonian radial-velocity model runs through an optional service on your own computer. The interface always labels what you see: an Education preview is a teaching model with stated limits, a scientific result comes from the validated model. The hosted app shows the scientific workspace as a clearly labelled replay of a stored example result.

Scientific workspace: the radial-velocity run form, the validated scope and the run provenance.

In the classroom

Start with the hands-on Transit Method experiment and record a light curve with phyphox.
Open Otherlight and rebuild the situation: set the star and planet radius and compare the simulated transit depth with your measurement.
Use a Guided Lab to formulate a hypothesis (e.g. "What happens to the transit chord if the inclination increases?"), test it in the simulation and write down the interpretation.
Extend the model: add a moon, a second star or a different orbit and discuss which signals real telescopes such as Kepler, TESS or JWST would see.

Good to know

The Education simulation is a teaching model with stated limits, not a research tool; the app says so on every screen.
Everything runs locally in the browser. Workspaces are saved as files that you control.
To run the app offline or locally, follow the instructions in the repository; it needs Node.js and pnpm.