Transit Usage Tips and Troubleshooting

User Guide

About Transit and Ephemeris

Using the Service:
  1. Accessing the Transit Service
  2. Building a Transit Prediction Query
  3. Building a Transit Service Query by URL
  4. Programmatic Results API
  5. Viewing Predictions
  6. Refining Transit Settings
  7. Transit Algorithms
  8. Definitions of Transit Parameters
  9. Usage Tips and Troubleshooting

Frequently Asked Questions

Why do the Event Ingress and Event Egress columns show different values from before?

As of the March 2018 update to the Transit Service, the event window columns in the output table have been modified: Event Ingress and Event Egress now contain the predicted ingress and egress times without padding for propagated uncertainties in the ephemerides; previously they included uncertainty padding. The new columns, 1σ Event Window Start and 1σ Event Window End, now take over the latter role, and report the predicted transit (or eclipse) window including the uncertainty padding.

Why is the service timing out?

When a large fraction of your input targets is unobservable, you may find that the transit service times out before it can return results. This can happen particularly at far southern latitudes, when the Kepler field remains permanently below the northern horizon. In this case, try running smaller subsets of your query, or single targets only.

Also, your web browser or the service may time out if you have uploaded object list(s) with cumulatively more than 500 targets.

How Can I Acknowledge/Cite the Transit Service?

Please include the following standard acknowledgment in any published material that makes use of the NASA Exoplanet Archive's services.

"This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program."

In addition, if you use data from a specific literature reference, please acknowledge that reference directly.

Additionally, the American Astronomical Society (AAS) has a standardized list of facility keywords that include the NASA Exoplanet Archive. When preparing a LaTeX manuscript for submission, use \facility {Exoplanet Archive}. For more usage tips and the full list of standardized facility names, see the AAS web site.

Notes and Caveats

  • Time systems: The Exoplanet Archive does not perform any conversion on the published planet ephemerides, and therefore predicted transit times may include a ±8 minute error depending on the time system in which the ephemeris was calculated and published.
  • We do not account for atmospheric refraction in calculating stellar rise/set times; times should only be considered accurate to ~1 minute. We also do not currently precess stellar coordinates to the epoch of the predicted transit. This can translate to additional systematic errors in target rise/set times on the order of ~1 minute per decade between the epoch of the transit and the epoch of the stellar coordinates.
  • Twilight end/start times are only approximate. The apparent proper motion of the Sun during the course of the night is not currently accounted for. This leads to uncertainties of up ~2-4 minutes in the twilight start/end times.
  • Rise and set times become more uncertain at very high and very low observatory latitudes, approaching the arctic/antarctic circles. Here the diurnal path of Sun and stars may begin to graze the horizon, and random unpredictable atmospheric refraction effects may also significantly affect the actual rise and set times. Ground-based observatory locations are currently limited to latitudes between ±65°.
  • Epoch of periastron: The orbital elements algorithm assumes that argument (or 'longitude') of periastron, ω, refers to that of the star in its reflex orbit, rather than that of the planet; we also assume that positive radial velocity indicates motion along the line of sight moving away from the observer. Note that there is a mix of conventions in the literature, and it is not always clear which convention is used. Values in the Exoplanet Archive tables are as-published, and where a different convention is used by authors, the ephemerides predicted with this method may be substantially incorrect (for example, for a circular orbit, predictions will be off by half the orbital period). Results of this algorithm should therefore be treated with caution!

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    Last updated: 4 May 2026