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8 June 2004: Transit of Venus


Please note: This page refers to the venus transit in 2004. The venus transit in 2012, which will take place on 6 June, will not be visible from South Africa.

Transits of Venus, in which the planet passes between Earth and the Sun, are rare phenomena. There have only been six transits since the invention of the telescope. Nobody alive today has seen a transit of Venus, because the most recent one occurred in 1882.

On June 08, Venus will again transit the Sun. The entire event will be visible in Asia except the extreme eastern portion, Africa except the western portion, Europe except the extreme southwestern Iberian Peninsula, Greenland except the southern tip, and most of the Indian Ocean.

Local circumstances of the transit appear on p.43 of the ASSA SkyGuide, or can be obtained using the free software provided by the Dutch Occultation Association.


Free software

The Dutch Occultation Association has developed a freeware program to make local predictions, with 1-second accuracy, for the circumstances of the transit.

Updates are available on the Dutch Occultation Association website

Version 2.0.1 can be downloaded directly from the ASSA site.

Make your own telescope

Prof Dennis Engel explains how to make a simple solar telescope to safely view the transit.


Since the disk of Venus will be 58 arcseconds across, it should be visible to the naked eye as a small dark spot on the solar surface.


WARNING: Caution must be exercised in observing the transit - viewing the Sun without proper eye protection is extremely dangerous and will probably lead to blindness.



The principal events occurring during a transit are characterized by contacts. The event begins with first contact (labelled '1' in the diagram), which is the instant when the planet's disk is externally tangent with the Sun. This is the start of the ingress phase. The entire disk of Venus is first seen at second contact ('2') when the planet is internally tangent with the Sun. During the next several hours, Venus gradually traverses the solar disk at about four arcminutes per hour. Greatest transit ('3') is the instant of minimum angular separation between Venus and the Sun as seen from Earth. At third contact (labelled '4'), the planet reaches the opposite limb and is once again internally tangent with the Sun, marking the start of the egress phase. The transit ends at fourth contact ('5') when the planet's limb is externally tangent to the Sun.



Historically, transits were important, since by precisely timing the motion of Venus across the Sun, they provided a method of determining the Earth-Sun distance and hence the scale of the solar system. The British surveyors, Charles Mason and Jeremiah Dixon (famous for establishing the "Mason-Dixon line" in the USA), observed the 1761 transit from Cape Town. The 1882 transit was well-observed from Southern Africa: at the Royal Observatory, Cape Town by Sir David Gill, at Aberdeen by staff of the Royal Observatory, at Touwsriver by the British, and at Wellington by the Americans. The Natal Observatory was established in Durban for this purpose.

Willie Koorts (SAAO) recently published two articles in MNASSA about the transit; these can be downloaded as PDF files:

Koorts, W.P. (2004) The 1882 transit of Venus: The British expeditions to South Africa. MNASSA, 63, 34.

Koorts, W.P. (2003) The 1882 transit of Venus and the Huguenot Seminary for Girls. MNASSA, 62, 198.


Local transit events


Braam van Zyl, Director of the Solar Section, writes:

"The Boyden Observatory at Bloemfontein is hosting a public day on the day of the transit. They have kindly invited us to make use of their facilities. Although they have assured us of technical support and good will regarding the project, it will be solely the undertaking of the amateur club.

We will use the 20cm coelostat with hydrogen filters, CCD cameras and at least three 10-inch reflectors with photographic capacity. We undertake to measure the four exact contact times and to photograph the entire event. We will also have a webcast of the transit.

Contact: Braam van Zyl (


The SAAO is webcasting the transit from Sutherland. SAAO homepage: [].

Contact: Dr. Dave Laney (


On Friday June 4, 18:30, the Pretoria Centre is presenting a public talk at Fort Schanskop. The entry fee is R25 per person (max.R50 per family), but if you bring your telescope to entertain the public, entry is free. The three-part presentation (how transits work, history of transit observations, how to observe it safely) is preceded by a viewing session, with comet LINEAR, Saturn, Mars and Jupiter on show.

Contact: Neville Young [].

The ASSA Pretoria Centre will be covering the transit by webcasting the event over the
internet. The webcast will take place from the grounds of the University of Pretoria. Check
out the action at [].

Contact: Mauritz Geyser []

Cape Town

Weather permitting, a telescope will be set up in front of the SA Museum (Cape Town), with planetarium staff in attendance. In history, such transits of Venus, when observed from different locations on Earth, were important scientific events used for determining the scale of the Solar System. Many western nations despatched expeditions to measure the timings of the transit of Venus, the most famous being the first voyage of Captain James Cook to the Pacific to observe the transit of 1761.

Contact: Iziko Museums of Cape Town, Tel: 021-481-3943

Touws River Festival

The transit of Venus on June 8 will be celebrated in the small Karoo town of Touws River (site of the 1882 British transit expedition observing station). For details contact Mrs. Helen Louw (tel: 023-3581192, []) or André Mellet (tel: 023-3581091, fax: 023-3581261, mobile: 0834547008, []).


Make your own telescope to view the transit

Prof Dennis Engel explains what transits are, and gives clear instructions on how to build a simple telescope that will effectively show the transit.


Websites worth a visit
The core of the site is a browsable database of historical instruments and images from collections around the world. The site is an initiative of the Scientific Instrument Commission of the International Union of the History and Philosophy of Science. It was developed at the University of Oxford and is hosted by the Museum of the
History of Science.
Presented in conjunction with the Smithsonian Institution Libraries exhibition "Chasing Venus: Observing the Transits of Venus, 1631-2004".
"2004 Transit of Venus" by Fred Espenak
Published in Observer's Handbook 2004, Royal Astronomical Society of Canada
"2004 and 2012 Transits of Venus", by Fred Espenak (NASA's GSFC)
"James Cook and the Transit of Venus"
The best reason to watch the 2004 transit of Venus is history.




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(c) ASSA 2003, 2004  - updated 2004 september 20