Transit Computer

You can obtain the circumstances of selected transits of Mercury and Venus for any location by following these simple steps:

Decide on which form below to use. If you want local circumstances for cities or towns in the U.S. or its territories, use Form A. For other locations, use Form B.
Select the transit from the first dropdown list in the form that you are using.
Specify the location, using the fields provided in the form.
Click the "Get data" button at the end of the form to compute a table of local circumstances.
Be sure to read Notes on the Data (on this page below the two forms) 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.

Form A - U.S. Cities or Towns

Transit:

State or Territory:

City or Town Name:

The place name you enter above must be a city or town in the U.S. The place's location will be retrieved from a file with over 22,000 places listed. Either upper- or lower-case letters or a combination can be used. Spell out place name prefixes, as in "East Orange", "Fort Lauderdale", "Mount Vernon", etc. The only exception is "St.", which is entered as an abbreviation with a period, as in "St. Louis". You need only enter as many characters as will unambiguously identify the place. The city or town name may be left blank if the State or Territory is District of Columbia.

Form B - Locations Worldwide

Transit:

Place Name Label:

The place name you enter above is merely a label for the table header; you can enter any identifier, or none (avoid using punctuation characters). The data will be calculated for the longitude and latitude you enter below.

Note: With the exception of the seconds components, coordinate components should be entered as integers (no decimals).

Longitude: east west degrees minutes seconds

Latitude: north south degrees minutes seconds

Height: (-90 to 10999) meters

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

Notes

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:

NASA's Planetary Transits pages.
H.M. Nautical Almanac Office's Transits of Venus pages.

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