Venus Transit  (June 8, 2004)

Fig. 1.  Silhouette of Venus at the midpoint of its crossing in front of the Sun, as observed from South Africa on 2004 Jun 8 at approximately 08:20 UT (10:20 am local time).  IMPORTANT: direct observation and photography of the Sun requires a special safety filter. Fig. 2.  Venus transits can only occur within a few days of June 8 or December 9, when Earth is in exact alignment with the points where Venus's orbit crosses the plane of Earth's orbit.  If Venus also happens to be at the crossing point simultaneously, then a transit is observed.  (Source: Astronomy 2004; 32(6): 76.) Fig. 3.  Our time-lapse movie (2.8 Mb) of the entire Venus transit as observed from our location in South Africa.  In this movie, the Sun appears motionless because we used a motorized telescope mount to track it across the sky.  Portions of the transit were partially obscured by clouds.  Playing this movie requires web browser support of HTML5 video. Fig. 4.  Our observation site on a game reserve in South Africa (show Google map).  See text for explanation of the equipment we brought to photograph the event.

An Event No Living Human Had Seen About every 105-120 years, Venus and Earth line up exactly on the same side of the Sun.  The result of this alignment is called a transit.  No one alive had witnessed this event.  During a Venus transit, the silhouette of Venus is visible against the Sun (Fig. 1).  It is a live demonstration of the scale of the solar system.  If Earth were a pea located at one end of a football field, then Venus (about the same size as Earth) would be at the 28-yard line.  The Sun would be located at the opposite goal line, and it would be almost 1 yard in diameter.  Because Venus and Earth are so small compared to the distances between them and the Sun, Venus transits are very rare (Fig. 2).    A Venus transit occurred on the morning of June 8, 2004.  Only the ending of the transit was visible from the eastern half of North America, so we journeyed to South Africa (show Google map) to see the entire event.  Also, the weather conditions at our observation site were much more favorable than the often cloudy weather in the mid-Atlantic region of the United States.    We joined a tour group that had been organized to observe the transit. There were over 30 members of our group.  The transit lasted over 6 hours, and everyone stayed out to watch the entire event.  It was fun to share the experience with others in the group.  The organizer of the tour and the group members themselves brought a wide variety of equipment with which to observe Venus during its transit of the Sun.    We brought our own equipment to photograph the transit (Fig. 4).  This involved tracking the Sun for over 6 hours and taking a photograph every 45 seconds.  Fig. 1 is one of 519 frames we took.  We put together all 519 frames into a movie that you can download (Fig. 3). Below is an outline of the equipment and techniques we used. GPS location:  S 24 deg 10.841', E 28 deg 37.898', altitude 5010 ft (show Google map) Solar filter:  full-aperture Thousand Oaks type 2+ Telescope:  Meade ETX-90 (90 mm aperture, 1250 mm focal length) Telescope mount:  Losmandy GM-8 equatorial mount with digital clock drive Camera:  Canon Digital Rebel SLR (6-megapixel resolution, 1.6X magnification compared to standard 35 mm format) mounted at telescope's prime focus Exposure:  ISO 100, 1/100 second for each frame Computer:  Apple PowerBook G4 laptop with Canon's Remote Capture program set to acquire a photo every 45 seconds; total of 519 frames Image processing:  Converted all images to grayscale binary format using GraphicConverter program.  Calculated centroid of the Sun in each image with a custom C program.  Using the calculated centroids, aligned each original color frame with an AppleScript script controlling Photoshop.  Some frames manually aligned using custom JavaScript software.  Assembled frames into a movie using Apple Final Cut Pro software.    The evening of transit day was cold and very windy.  Not knowing if there would be any more opportunities to set up our equipment, John braved the elements to do some wide-field astrophotography of the Milky Way, perhaps a sight even more impressive than the Venus transit (Fig. 5). ( back to home page)

Fig. 5.  The Milky Way around the constellation Crux, the Southern Cross, in the night sky over our observation site in South Africa on the night of 2004 June 8.  This photograph was made with a Canon A1 SLR camera and Sigma 24 mm wide angle lens "piggybacked" on our telescope.  The exposure was 12 minutes at f/2.8 on Kodak E200 Professional 35 mm slide film.  With an illuminated reticle eyepiece, the telescope was used to aim the camera accurately during the exposure.

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