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Transit Computer

This data service calculates the circumstances of selected transits of Mercury and Venus. Use the following steps to determine the circumstances for any location.

  • Select the transit of interest from the drop-down list.
  • Specify the location of interest using the fields provided on the form. Use the buttons to find coordinates of cities or towns in the U.S. or its territories, or to convert between Degrees-Minutes-Seconds (DMS) and Decimal Degrees.
  • Click the "Get Data" button at the end of the form to compute a table of local circumstances.

Be sure to read the Notes on the Data for an explanation of the items in the table.

For additional information on transit circumstances and visibility, see Upcoming and Recent Transits of Mercury and Venus.


Location Coordinates in decimal degrees, North and East are positive. For example: 38.9072, -77.0369

Location Label Custom label for printed output. For example: Washington, DC

Need coordinates?  Try NGA's GEOnet Names Server (GNS)
Need U.S. coordinates?  Try the USGS Geographic Names Information System (GNIS) .

Height (-90 to 10999 meters)


Transit of Venus, 1882

This service provides local circumstances for transits of Mercury and Venus. For a selected transit, up to five phases of the transit are listed in the tabular output:   Transit Begins (Ingress Exterior Contact), Ingress Interior Contact, Least Angular Distance, Egress Interior Contact, and Transit Ends (Egress Exterior Contact). Depending upon the location, all, some, or none of phases are observable. The times at which these phases occur are given on a 24-hour clock (e.g. 13:00 = 1:00 p.m., etc.) in Universal Time. Use our table for locations in the United States or the world time zone map to convert from Universal Time to local time. If the transit is in progress when the Sun rises or sets, the time of sunrise or sunset may also appear in the table. The position angle of the contact points are reckoned from the north point of the limb of the Sun towards the east. Also included in the tabulation are the altitude (uncorrected for refraction ) and azimuth of the center of the Sun's disk, in degrees, as well as the angular separation of the center of Mercury or Venus and the center of the Sun, in arcminutes (there are 60 arcminutes in a degree). The semidiameter -- the angle at the specified location subtended by the radius of the object -- of the Sun, Mercury, and Venus is tabulated in arcminutes (') and arcseconds (").

Transit of Venus photographic plate (1882) image courtesy of the U.S. Naval Observatory Library .

For additional information, see: