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JWST coronagraphic target observability calculator

Project description

Current version: 0.2.0 (beta).

Download for macOS (31 MB) | Download Python source

Report any issues at or via email to the authors.

Authors: Christopher Stark (, Joseph Long (

Screenshot of the JWST Coronagraph Visibility Tool showing target HR 8799 with three companions plotted.

The allowed pointing of JWST leads to target visibility that depends on ecliptic latitude, and the range of roll angles allowed depends on solar elongation. The allowed PAs for a target can thus be a complicated function of time. As a result, it can be difficult to 1) understand the possible orientations of a given target on the detector, 2) determine the ideal roll angle offsets for multi-roll observations, and 3) determine a group of targets that are simultaneously visible. The JWST Coronagraph Visibility Tool (CVT) was created to address these issues and assist with creating APT programs and diagnosing scheduling errors.

We stress that the CVT is designed to provide quick illustrations of the possible observable orientations for a given target. As such, the CVT rapidly approximates JWST’s pointing restrictions and does not query the official JWST Proposal Constraint Generator (PCG). The CVT does not include detailed pointing restrictions like Earth and Moon avoidance, etc. Additionally, results may differ from official constraints by a degree or so. Users should treat the results as close approximations.

Additionally, detector geometry (e.g. conversion from sky coordinates to the instrument’s Idl frame) is provided by the SIAF (Science Image Aperture File). The SIAF is a standardized format for manipulating instrument apertures and coordinate conversions, maintained by STScI as part of operating JWST. As of this writing (April 2016), the code includes its own copies of the PRDDEVSOC-D-012 version of the NIRCam and MIRI SIAFs.

For installation instructions and usage instructions, see the documentation on GitHub or docs/index.rst in this repository.

Known Issues

  • The CVT does not (and will not) query the JWST Proposal Constraint Generator. The only constraint on the field of regard is the Sun and anti-Sun avoidance angle.
  • Target name resolution depends on the availability of the SIMBAD service. If the service cannot be reached, you will have to enter coordinates yourself.
  • The CVT does not currently provide a way to export the plotted points as text. Plots can be saved from the GUI using the save icon below the plot panel.
  • The CVT has only been tested on Mac and Linux. Issue reports from Windows users are welcome, and we will do our best to address them, but we are not testing the tool on Windows.

See issue tracker at

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