Historical Studies

Historical studies of expeditions, and observational methods and results, for previous transits of Mercury and Venus, particularly the Transits of Venus of 1761, 1769, 1874 and 1882 are of interest.  Although Woolf's The Transits of Venus summarizes the two Eighteenth-Century transits of Venus, no comparable work has been produced for the Nineteenth-Century transits, nor for the numerous transits of Mercury that have been observed from 1631 through 1993.  Through the research efforts of participants, this section hopes to compile a computer database of historical transit observations

Incorporating information from this database, the coordinator hopes to produce a semi-technical book on the history and observation of transits of Venus and Mercury, to be published prior to the Transit of Venus of 2004.  Naturally, all participants to this project will be given due credit for their contributions.

Observational Studies

Planning and coordinating observation of future transits of Mercury and Venus across the Sun is now in progress. Particular attention is being given to the rare partial ("graze") transit of Mercury in 1999 and the transits of Venus in 2004 and 2012. These Venus transits will be the first since 1882. In the next 15 years, there will be additional transits of Mercury in 2003 and 2006. Given clear skies, observers everywhere should be able to see one or more of the phenomena listed below.

Observations can be visual, photographic, video, or CCD.  Use a telescope and magnification or focal length sufficient to fully resolve the disk of the planet. Besides traveling to the transit zones with portable telescopes, observers are encouraged to remain at home if a transit is visible from there, so as to employ larger telescopes. Large image scales are desirable.  In general, equipment and techniques suitable for high-resolution sunspot studies will be appropriate for detailed transit observations. 

Most of the phenomena of interest take place during ingress and egress, so observers who cannot view an entire transit, but just its beginning or end, should not despair.  Of particular interest is the recording of:  

• The "black drop" effect in video or rapid-sequence CCD for both Venus and Mercury transits (especially for the prolonged partial transit of Mercury in 1999).

• The bright halo around Venus when it is entering or leaving the solar disk.

• Any anomalous optical phenomena such as a bright ring around a planet when it is fully on the solar disk, visibility of a planet when it is fully off the solar disk, and brightening of any sort within the disk of the planet.

• Timing of the four transit contacts in order to compare video and CCD contact times with the historical visual and photographic timings.