2012/06/05 Transit of Venus

This is the first (and also the last) Venus transit experience in my life (I don’t expect that I will still be alive 105 years later).

Transit of Venus Composite Photo
More photos are listed in transit photo gallery

Since most part of transit (1st/2nd contact and mid-transit) would be visible, I decided not to travel unless the weather became an issue.

The forecast did look good on the transit day – scattered mid clouds in the morning and clear sky in the afternoon. It was not the best – it was clear (without even a trace of the cloud) with excellent transparency and seeing for the next few days ; it was not the worst either – it was rainy and windy the day before (very unusual at this time of the year).

At 12PM, scattered passing Cumulus clouds still covered 30-40% of the sky and it did not look to be clear soon. I decided to drove up to the site near the coast (on the west), because the satellite image showed that the sky near the coast was clear so it would unlikely be clouded out during the 1st/2nd contact. The sky got completely cleared up (almost cloudless) at 1:45PM so the decision was not bad. But probably I should have gone to Henry Coe (on the east), where the sky became mostly clear at 3PM, and remained in very good condition after mid-transit when the clouds moved into the coast. But I did not want to take chance, being clouded out during the 1st/2nd contact would ruin the entire viewing experience.

I set up the telescopes on a pullout on HW35, near the junction with HW92. The pullout was on the mountain ridge overlooking the Pacific Ocean to the west . Usually it is breezy at the coast ridge. It was no different on the transit day (~15m/h), and it did not seem particularly worse than other places since the forecast was breezy for the entire valley.

Viewing Site

My kids and I spent a few minutes to view the sunspot to figure out the 1st contact position. It did not take much time, thanks to the composite photo (sun image + predicted transit path) posted on Spaceweater.com.

My Younger Kid Was Viewing Sunspots Before The Transit
CGEM mount, AT111EDT (white) for imaging, AT72ED (black) for visual with 9mm Nagler T6 EP

At 3h06m, my older kid and I started to look for the venus. My kid observed visually using AT72, and I used Canon T3i on AT111 (liveview). At 3h07m03s, by coincidence, we both noticed a small bump/dent on the edge of sun at the predicted position. The dent got bigger and bigger and soon 1/3 of the venus became visible.

There were two special phenomena we were planning to look for – aureole and black drop.
All I knew about the transit was black drop, until I learned aureola from the article in Sky & Telescope two weeks before the transit.

When the venus was half way entered the sun, my son claimed that he could sense the entire disk of the venus. He had shaper vision but I doubted whether it was just an illusion.

At 3h16m, we noticed a bright, thick, light orange arc (spanning ~45 deg, starting from the left point where Venus and Sun intersected) through AT72. My son also noticed the much smaller, dimmer arc on right side intersection point. At 3h19m, ~3/4 of Venus moved into the sun, the aureole – “ring of limb” – appeared. It was hair thin in the middle and slightly thicker (~2x thicker) near both intersection points. It was light orange too but much fainter than the “arc”, and was easy to miss. My son told me later that the ring was broken at 2-3 places in the middle. I did not notice it and I am wondering if it is “baily bead” of transit.

Around 3h24m00s, right after predicted 2nd contact, my son exclaimed that the black drop had started. Initially it was wider and darker, then gradually became narrower and lighter as Venus was moving away front the edge of the Sun. On 3h2420s, the black drop was gone visually and venus moved completely inside the sun. 2-3s prior to it the black drop because a thin line, so my son was able to tell the black drop was about to finish.

I took a few pictures of black drop. Though not as clear as I hoped due to the wind, it did seem that the black drop was not as prominent as visual observation, probably due to a better optics.

After 2nd contact, the venus crept over the sun. It became so boring that my kids stayed in the car playing the game. I took the picture every 5 minutes.The sky remained clear with average seeing until 6:15m. Then high clouds moved in, the seeing became so poor that sun and venus looked like were swimming in the ocean. I could see the turbulence in 9×50 finderscope, which was barely noticeable in AT72ED during the first half of the transit.

At 7h30m, more high clouds moved in and seeing remained very poor so I decided to give up.

It was a truly unforgettable experience. We felt so lucky that we not only experienced the once-in-a-lifetime event, but also witnessed both rare phenomena.

The biggest lesson I learned was that I should have used the fastest shutter speed to take the transit photos. I used 1/500s for all my photos and most of them show blurred venus due to wind and seeing. It would have been much better if I had used 1/1000s or faster.


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