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Venus transit observation of June 8, 2004

The morning of June 8, 2004 ...

02h53m local time : I receive an email message announcing the shipment of a Celestron C14 optical tube assembly to my observatory. This is a long awaited message, that (almost) concludes a one year process of preparing the set up a second telescope at CBA Belgium Observatory.

02h59m local time : I conclude a time-series CCD photometry session on V380 Oph, a prime target of the CBA. A couple of minutes later, my telescope slews to LL And, another great target of opportunity for photometry, last seen in outburst in 1993. Twilight is approaching, but the importance of this outburst makes the short session worthwhile. And with some luck, professional astronomers at MDM Observatory will be able to take over some time after my session concludes, using a 1.3-m telescope.

07h00m local time : I remove the CCD camera from the telescope, attach a Baader Solar filter to the front of the telescope, and instruct TheSky to slew it to the Sun. A minute later, I'm looking at a stable image of the Sun. Sky conditions are perfect - not a single cloud-, and the temperature is rising steadily. It's gonna become the warmest day of this year, with a temperature of about 31 degrees. I trust the forecast.

Life of an amateur astronomer can be exciting, isn't it ?

The Venus transit - ingress

I started my Venus observing session around 5h UT, about 20 minutes before the start of the transit. Around 5h20m UT, first contact (ingress) was seen, and a few minutes later, the transit became really easy to spot in the telescope (also for less experienced observers). I connected my Olympus C3030 Zoom digital camera to the telescope, using a Digi-T Kit connector, and started making first images.


Images made with an Olympus C3030 Zoom digital camera, attached to a 0.35-m f/6.3 telescope (effectively reduced to 0.08-m). The image at left was obtained on 2004, June 8.23 UT, during ingress. The one at right shows Venus during transit. (c) Tonny Vanmunster

Around 5h40m UT, Venus' silhouette became detached from the Sun's limb. I visually looked for the famous "black-drop effect", but could not see it in my 0.35-m f/6.3 telescope (aperture reduced to 8 cm). However, shortly before the very black disk of Venus completely slided into the Sun's bright edge, it grew a small, easy to spot halo (aureole) of light around its dark edge. The halo lasted a few minutes and then vanished. I realised I was looking at Venus' atmosphere. Actually, the aureole is caused by sunlight passing through the planet's dense atmosphere. This was a beautiful, and unexpected phenomenon. Shortly after, I saw numerous reports on a mailing list of the Flemish Astronomical Association VVS, also mentioning the halo observations.
		Venus' atmosphere is easily visible in this image made by Jan Koeman, Stichting Volkssterrenwacht Philippus Lansbergen, The Netherlands.

Visitors at CBA Belgium Observatory

Venus' transit would last for >6 hours in Belgium, so there was plenty of time to share the event with others. I hosted the local school (Gemeentelijke Basisschool Walshoutem), where both of my sons stay, for an observing session. It turned out to be a great experience : the children first got some information about the Solar system (relative sizes and distances of the inner planets), and then observed Venus with special eclipse glasses. Highlight of course was a visit to the observatory, where they could visually spot the dark disk of Venus through the telescope.


A small model of the Solar System was built (the Sun's model disk is seen on the outside wall of the observatory) to demonstrate relative sizes and distances to the school children.		Being able to see Venus through a real telescope definitely was the most impressive part of the visit.

Egress - timings, black-drop effect, atmosphere

Around 11h04m UT, Venus' silhouette reached the Sun's limb for its final egress. This time, I decided to make digital images of the approach. Much to my surprise, the black-drop effect appeared on the images, while I hadn't seen it visually during ingress. In my opinion, this once more proofs that the effect is mainly due to contrast aspects and Earth's atmospheric conditions (which were much better at ingress).

			The black drop effect becomes visible just before the start of third contact. 0.35-m f/6.3 telescope (effective aperture 8-cm) and Olympus C-3030Z camera. Tonny Vanmunster.

Shortly after the start of egress, I switched back to visual observing, and immediately noticed Venus' atmosphere again. My wife Kathleen also easily spotted it, although I didn't mention where to look. Again, the halo disappeared after a few minutes, shortly before half of Venus' disk had left the Sun's limb.

I concluded the transit observation by trying to make an accurate timing of fourth contact. I found a value of 11h23m20s UT.

Future Venus transits

The next Venus transit occurs on June 6th, 2012 and only the final part will be visible from Belgium. After that, one has to 'wait' till 2117 for a next transit. I came across following quote from William Harkness, Director of the U.S. Naval Observatory in 1882, at the moment of the previous Venus transit.

"We are now on the eve of the second transit of a pair, after which there will be no other till the twenty-first century of our era has dawned upon the earth, and the June flowers are blooming in 2004. When the last transit season occurred the intellectual world was awakening from the slumber of ages, and that wondrous scientific activity which has led to our present advanced knowledge was just beginning. What will be the state of science when the next transit season arrives God only knows. Not even our children's children will live to take part in the astronomy of that day. As for ourselves, we have to do with the present ..."

What will be the state of science in 2117 ? God only knows ...