Transit Computer: U.S. Cities and Towns
This form is for U.S. cities and towns only. For all other locations, in the U.S. or worldwide, specify the latitude and longitude using this form. You can obtain the circumstances of selected transits of Mercury and Venus by following these simple steps:
- Select the transit from the first dropdown list.
- 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 (at the end of the form) 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.
Notes on the Data:
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.
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 on recent and upcoming transits, see:
