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Venus transits the Sun 2004/06/08

On 2004 June 8, Venus passed in front of the Sun for the first time since 1882. Historically, these "Transits of Venus" were of great importance, as they enabled the size of the solar system to be measured. Today this is done using radar. However it is possible for individuals across most of Africa to make simple observations of this transit and so establish for themselves the size of the solar system. This made it a valuable educational exercise.

Most HartRAO staff observed the transit from the observatory, while three staff members assisted with the mass public viewing at the much more accessible Johannesburg Planetarium.

Pictures of the transit from the Johannesburg Planetarium.

Venus transit at Hartebeesthoek

Left click on image for large version [S Goedhart]

The weather over the Hartebeesthoek Radio Astronomy Observatory at the start of the transit was not auspicious. A cold front was passing over, bringing rapidly moving low cloud. The image above was taken one minute before first contact.

Left click on image for large version [S Goedhart]

Just after first contact, astronomer Marion West views the Sun through the spotting scope equipped with a solar filter, while astronomer Mike Gaylard, on the left, and SLR manager Wilhelm Haupt look on.

Left click on image for large version [S Goedhart]

Projected image of the Sun just before second contact.

Left click on image for large version [M Gaylard]

At Hartebeesthoek, the transit was viewed using eclipse viewers, with a spotting scope fitted with a solar filter, and by projection using a 10cm Meade telescope, as shown above.

Left click on image for large version [M Gaylard]

A close-up image of Venus transiting the Sun is shown above. The image is reversed by the telescope, so Venus appears on the left, whereas by direct viewing it appeared on the right from this site at the beginning of the transit. First contact occurred at the "four o'clock" position on the Sun as seen from here. Low clouds accompanying a cold front obscured much of the start of the transit, but a fortuitous gap in the clouds enabled the Hartebeesthoek observers to time second contact at 07h 36m 05s SAST (UT+2h).

Left click on image for large version [M Gaylard]

Contact timings were made by the author using this Leica Televid 77 spotting scope equipped with Baader solar filter. Here third contact is about to occur, timed at 13h 10m 00s SAST.

[S Goedhart]

Close-up of projected image around third contact. Note that there is uncorrected chromatic aberration in the eyepiece, producing distinctly offset image at the red and blue ends of the spectrum, making timing difficult by this method.


And the transit is nearly over.


The timing results were submitted to the European Southern Observatory (ESO) Venus Transit website (see below). The plot above of the result compared to others submitted is from the observers page at the VT-2004 Observation Campaign, but see also the results on the ESO website. The value in green above is that derived from the Hartebeesthoek measurements.

HartRAO staff astronomer Sarah Buchner and educators Daphne Kedibone Lekgwathi and Mzi Taele helped run the mass viewing of the transit from the Johannesburg Planetarium, which was attended by hundreds of learners and public.

Background to the Venus Transit

It was possible to watch the transit using the same methods used to watch the recent total eclipses of the Sun. These methods included: The same safety precautions applied as for a solar eclipse: Looking at the Sun in either of these ways can damage your eyes permanently. Venus appeared as a small black dot passing across the face of the Sun. The angular diameter of the Sun is 30 minutes of arc (= 0.5 degrees), while the angular diameter of Venus will just under 1 minute of arc (this changes as the distance of Venus from the Earth changes). Hence the diameter of Venus during the transit will appear to be 3 % of the diameter of the Sun. To make useful measurements we needed: There are four 'times of contact': How use was made of these measurements is described in the links below.


Several excellent websites were set up that cover this event.