Catalogs of transit circumstances include the following data. The calendar date^{1} and geocentric Universal Time^{2} of the four transit contacts^{3} and the instant of greatest transit^{4} are found in the first six columns. The Sun's coordinates (Right Ascension and Declination) and the Greenwich Sidereal Time at 00:00 UT are given next. The minimum separation between the centers of the planet and the Sun is listed in arc-seconds. Finally the transit series^{5} is given.
Column Heading Definition/Description 1 Date Calendar Date (Gregorian) at instant of Greatest Transit. (Julian calendar is used before 1582 Oct 15). 2 I Contact I is the instant when the planet's disk is externally tangent to the Sun (transit begins). 3 II Contact II is the instant when the entire disk of the planet is first internally tangent to the Sun. The period from contact I to II is called Ingress. 4 Greatest Universal Time (UT) of Greatest Transit, which is Transit defined as the instant when the planet passes closest to the center of the Sun as seen from the center of Earth. 5 III Contact III is the instant when the planet reaches the opposite limb of the Sun and is once again internally tangent to the Sun. 6 IV Contact IV is the instant when the planet's disk is externally tangent to the Sun (transit ends). The period from contact III to IV is called Egress. 7 Minimum Minimum angular separation (arc-seconds) Sep. between centers of the Sun and planet occurs at the instant of greatest transit. 8 Sun Geocentric Right Ascension (hours) of the Sun RA at greatest transit. 9 Sun Geocentric Declination (degrees) of the Sun Dec at greatest transit. 10 GST Greenwich Sidereal Time at 00:00 UT. 11 Transit Recurrence series of transit. Series Mercury transits recur after an interval of 46 years. Venus transits recur after an interval of 243 years.
To determine whether a transit is visible from a specific geographic location, it is simply a matter of calculating the Sun's altitude and azimuth during each phase of the transit. The calculations can be performed on any pocket calculator having trig functions (SIN, COS, TAN). Armed with the latitude and longitude of the location, the transit catalogs provide all the additional information needed to make the calculations.
For a detailed description of how to calculate the Sun's altitude and azimuth, see Visibility of Transits. This web page also has links to Excel spreadsheets which can be used to calculate transit circumstances from any place on Earth.
Transit predictions are based on algorithms and elements published in "Transits" by Jean Meeus (Willmann-Bell, 1989).
The value for delta-T was determined as follows:
All transit calculations are by Fred Espenak, and he assumes full responsibility for their accuracy.
Permission is freely granted to reproduce this data when accompanied by an acknowledgment:
"Transit Predictions by Fred Espenak, NASA/GSFC"