doppler-shift-visualiser

Doppler Shift Visualiser

An interactive spectroscopy laboratory for comparing the first-order and longitudinal special-relativistic Doppler relations, following source-frame stellar lines, and separating them from an observer-frame telluric feature.

Live laboratory

Open the interactive visualiser

The browser view provides:

exact 1 + z = sqrt((1 + beta)/(1 - beta)) wavelength shifts over ±300 km/s;
the first-order z ≈ v/c approximation and its residual from the exact result;
a labelled Na I D doublet plus representative stellar features;
an O₂ B telluric feature that remains fixed in the observer frame;
a deliberately exaggerated wavefront animation, clearly separate from the numerical calculation; and
a photon-noise precision relation stated in the Bouchy–Pepe–Queloz quality-factor form.

This is an educational forward model, not a wavelength-calibration pipeline, synthetic spectrograph, cross-correlation implementation, or exoplanet detection claim.

Numerical model

For one-dimensional relative motion in flat spacetime,

beta = v / c
lambda_obs / lambda_0 = 1 + z = sqrt((1 + beta) / (1 - beta))

For |v| << c, z ≈ v/c and lambda_obs ≈ lambda_0(1 + v/c). The interface computes the exact relation and reports the first-order discrepancy. It does not use this special-relativistic relation to explain cosmological redshift.

The photon-limited RV uncertainty context is

sigma_v = c / (Q sqrt(N_e))

where Q summarizes the Doppler information content of the sampled spectrum and N_e is the detected photoelectron count. This is a lower bound conditional on the spectrum and detector sampling; stellar activity, calibration, tellurics, and instrumental systematics are additional.

Run locally

Serve the repository so browser modules load correctly:

python -m http.server 8000

Then open http://localhost:8000/web/.

The separate Python demonstration can be run with:

python -m pip install -r requirements.txt
python main.py

Verification

npm test
npm run validate:research
python -m unittest discover -s tests -p "test_*.py"

The JavaScript tests cover zero shift, low-velocity agreement, relativistic reciprocal symmetry, sign conventions, invalid inputs, and the photon-noise quality-factor relation. The Python tests independently exercise the numerical shift functions and output-path handling.

Evidence and boundaries

Citation

See CITATION.cff. Code is MIT licensed. The project is independent and is not affiliated with NIST, ESO, NASA, ESA, or any instrument consortium.

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