<p>
  This tool estimates spectral contamination and scheduling visibility for
  supported JWST slitless time-series modes. It places Gaia field sources on
  the detector at each position angle, simulates overlap with the target
  spectrum, and reports the expected contamination as a function of position
  angle. The visibility calculation provides the dates and telescope
  orientations available for the selected target, instrument, and epoch.
</p>

<h4>Important limitations</h4>
<ul>
  <li>Field sources come from Gaia DR3. Coordinates are propagated from the
      Gaia reference epoch to the selected epoch when proper-motion
      measurements are available. Sources absent from Gaia or lacking a valid
      Gaia G-band flux are not included.</li>
  <li>Relative source brightness is currently normalized using Gaia G-band
      flux. This approximation can be inaccurate when the target and
      contaminant have substantially different optical-to-infrared colors.</li>
  <li>Trace-placement and distortion uncertainties can shift predicted
      spectral overlap by several detector pixels.</li>
</ul>
<p>
  Questions or unexpected results can be reported through the
  <a href="https://jwsthelp.stsci.edu/">JWST Help Desk</a>.
</p>