Fast and painless exoplanet transit light curve modelling.

astronomy, astrophysics, exoplanets, light-curve-models, python, transit-model, transiting-exoplanets
pip install PyTransit==2.6.1



Licence MNRAS arXiv ASCL DOI

Fast and easy-to-use tools for exoplanet transit light curve modelling with Python. PyTransit offers optimised CPU and GPU implementations of popular exoplanet transit models with a unified interface, and thrives to be the fastest and the most versatile tool for transit modelling in Python.

PyTransit makes transit model evaluation trivial whether modelling straightforward single-passband transit light curves or more complex science-cases, such as transmission spectroscopy. Further, the model can be evaluated for a large set of parameter sets simultaneously in parallel to optimize the evaluation speed with population-based MCMC samplers and optimization methods, such as emcee and DE-MCMC.

from pytransit import RoadRunnerModel

tm = RoadRunnerModel('quadratic')

tm.evaluate(k=0.1, ldc=[0.2, 0.1], t0=0.0, p=1.0, a=3.0, i=0.5*pi)

tm.evaluate(k=[0.10, 0.12], ldc=[[0.2, 0.1, 0.5, 0.1]], t0=0.0, p=1.0, a=3.0, i=0.5*pi)

tm.evaluate(k=[[0.10, 0.12], [0.11, 0.13]], ldc=[[0.2, 0.1, 0.5, 0.1],[0.4, 0.2, 0.75, 0.1]],
            t0=[0.0, 0.01], p=[1, 1], a=[3.0, 2.9], i=[.5*pi, .5*pi])

The package has been used in research since 2010, and is described in Parviainen (2015), Parviainen (2020a), and Parviainen (2020b).

Examples and tutorials

RoadRunner transit model

RoadRunner (Parviainen, 2020a) is a fast exoplanet transit model that can use any radially symmetric function to model stellar limb darkening while still being faster to evaluate than the analytical transit model for quadratic limb darkening.

  • RRModel example 1 shows how to use RoadRunner with the included limb darkening models.
  • RRModel example 2 shows how to use RoadRunner with your own limb darkening model.
  • RRModel example 3 shows how to use an LDTk-based limb darkening model LDTkM with RoadRunner.

Transmission spectroscopy transit model

Transmission spectroscopy transit model (TSModel) is a special version of the RoadRunner model dedicated to modelling transmission spectrum light curves.


Read the docs at


  • 21.10.2020, version 2.5

    • Version 2.5 makes modelling of TTVs trivial with pytransit.RoadRunnerModel and pytransit.QuadraticModel.
    • See the TTV modelling example notebook for an example of how to evaluate the models for a TTV analysis.
  • 14.10.2020, version 2.4

  • 16.9.2020, Version 2.3

    • Version 2.3 adds OblateStarModel to model transits over gravity-darkened rapidly rotating star as presented by Barnes (2009).
    • See the oblate star model example notebook for an example of usage.
  • 13.9.2020, Version 2.2

    • Version 2.2 brings a significant speedup to the evaluation speed of all models. The normalised planet-star distances are now calculated using a Taylor-series expansion of the planet's (x,y) sky-plane position. The method gives a 2-6 x speedup to the transit model evaluation and is detailed in Parviainen & Korth (2020, submitted to MNRAS)
  • 7.7.2020, Version 2.1



The easiest way to install PyTransit is by using pip

pip install pytransit


Clone the repository from github and do the normal python package installation

git clone
cd PyTransit
python install


If you use PyTransit in your reserach, please cite

Parviainen, H. MNRAS 450, 3233–3238 (2015) (DOI:10.1093/mnras/stv894).

or use this ready-made BibTeX entry

  author = {Parviainen, Hannu},
  doi = {10.1093/mnras/stv894},
  journal = {MNRAS},
  number = {April},
  pages = {3233--3238},
  title = {{PYTRANSIT: fast and easy exoplanet transit modelling in PYTHON}},
  url = {},
  volume = {450},
  year = {2015}