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Build Status: Conda Build Status: Pip Documentation Status DOI GPLv3+ License Python version

Table of Contents


Sherpa is a modeling and fitting application for Python. It contains a powerful language for combining simple models into complex expressions that can be fit to the data using a variety of statistics and optimization methods. It is easily extensible to include user models, statistics, and optimization methods. It provides a high-level User Interface for interactive data-analysis work, such as within a Jupyter notebook, and it can also be used as a library component, providing fitting and modeling capabilities to an application.

What can you do with Sherpa?

  • fit 1D (multiple) data including: spectra, surface brightness profiles, light curves, general ASCII arrays
  • fit 2D images/surfaces in Poisson/Gaussian regime
  • build complex model expressions
  • import and use your own models
  • use appropriate statistics for modeling Poisson or Gaussian data
  • import new statistics, with priors if required by analysis
  • visualize the parameter space with simulations or using 1D/2D cuts of the parameter space
  • calculate confidence levels on the best fit model parameters
  • choose a robust optimization method for the fit: Levenberg-Marquardt, Nelder-Mead Simplex or Monte Carlo/Differential Evolution.

Documentation for Sherpa is available at Read The Docs and also for Sherpa in CIAO.

A Quick Start Tutorial is included in the notebooks folder and can be opened with an ipython notebook.


This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. A copy of the GNU General Public License can be found in the LICENSE file provided with the source code, or from the Free Software Foundation.

How To Install Sherpa

Full installation instructions are part of the Read The Docs documentation, and should be read if the following is not sufficient.

It is strongly recommended that some form of virtual environment is used with Sherpa.

Sherpa is tested against Python versions 3.9, 3.10, and 3.11.

The last version of Sherpa which supported Python 2.7 is Sherpa 4.11.1.

Using Conda

Sherpa is provided for both Linux and macOS operating systems running Python 3.9, 3.10, and 3.11. It can be installed with the conda package manager by saying

$ conda install -c -c conda-forge sherpa

Using pip

Sherpa is also available on PyPI and so can be installed with the following command (which requires that the NumPy package is already installed).

% pip install sherpa

Building from source

Source installation is available for platforms incompatible with the binary builds, or for when the default build options are not sufficient (such as including support for the XSPEC model library). The steps are described in the building from source documentation.


Sherpa is developed by the Chandra X-ray Observatory to provide fitting and modelling capabilities to the CIAO analysis package. It has been released onto GitHub for users to extend (whether to other areas of Astronomy or in other domains).

Release History

4.16.0: 17 October 2023 DOI

4.15.1: 18 May 2023 DOI

4.15.0: 11 October 2022 DOI

4.14.1: 20 May 2022 DOI

4.14.0: 07 October 2021 DOI

4.13.1: 18 May 2021 DOI

4.13.0: 08 January 2021 DOI

4.12.2: 27 October 2020 DOI

4.12.1: 14 July 2020 DOI

4.12.0: 30 January 2020 DOI

4.11.1: 1 August 2019 DOI

4.11.0: 20 February 2019 DOI

4.10.2: 14 December 2018 DOI

4.10.1: 16 October 2018 DOI

4.10.0: 11 May 2018 DOI

4.9.1: 01 August 2017 DOI

4.9.0: 27 January 2017 DOI

4.8.2: 23 September 2016 DOI

4.8.1: 15 April 2016 DOI

4.8.0: 27 January 2016 DOI