Transit of Venus
June 8, 2004
Mt. Horeb, Wisconsin

The sun finally appears out of the haze. (image by Geoff Holt)

Just after sunrise, with the sun filtered only by the morning haze low on the horizon. Note how flattened the disk of the sun appears.(This image and those following by John Rummel)

Close to the moment of 3rd contact. Compare with next image.

Taken just seconds after the above image. Note the flattening of Venus' edge where it's tangent with the sun.This may be related to the infamous "black drop" effect, whose cause is not precisely understood. The black drop frustrated the attempts of 18th and 19th century observers of transits who were attempting exact timings in order to calculate the parallax of Venus. The flattening effect observed here and the "black drop" are most likely the result of imperfect optics and atmospheric refraction. In my case, the Sun was less than 9 degrees above the horizon when these shots were taken, and it was a miserably humid and hazy morning. After inspecting hundreds of shots of the June 8 transit over the days following the event, I have observed a relationship between the clarity of the skies, the quality of the optics, and whether or not the "black drop" was observed. The better the skies and the optics, the less chance the effect was seen. The photo above was selected as Earth Science Picture of the day for June 9th, 2004.

Timing the fourth contact. These timings are of relative value only. I took them directly from the individual frames' EXIF data from the camera. Since I did not carefully calibrate the camera's clock prior to the transit, the timings are not accurate to an external standard time. A fun project anyway.

The 2004 Mt. Horeb Venus Transit expedition group!
Geoff Holt, John Rummel, Art Camosy, and several students from Art's Astronomy class.

All images copyright Geoff Holt or John Rummel. Please contact us for permission to use, and for high resolution copies.

Technical Details:
Telescopes: Celestron C8, Celestron "shorty" 80mm f/4.5
Camera: Nikon Coolpix 4500
Eyepieces: Scopetronix 14mm WA; Televue Plossl 40mm
Location: Golf course, Mt. Horeb, Wisconsin
Conditions: mostly clear, temperature 72, humidity high

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