Transit of Venus/Extreme Astronomy
I had been watching the weather for the past two weeks and it pretty consistently indicated that our chances of seeing the transit tonight would be low at best.
After checking on cloud cover and area rainfall, and the direction of movement of both I had pretty much decided to observe this one on the Web. Then Peter emailed saying he was going to go down to Battery Park, where we had planned to observe from, and asked if I was going to go. I said I would join him although I didn't expect to see anything.
It looked even worse outside than it did when I looked out my window at the little sliver of sky I am allotted, but I persevered and caught the train down to South Ferry.
On arrival the clouds were very dark and looked like impending rain. Then I found that the park was holding a fundraiser tonight and had the entire waterfront closed off and lined with party tents. We would not be able to observe from my preferred location. I scouted around and found that the only place we could get to the water was all the way up at the north end of the park near Pier A. I emailed Peter and went back to the flagpole to wait for him.
While waiting for Peter the clouds started to thin enough that I could see where the Sun was. I set up my telescope in case the clouds thinned enough to do some observing. That was right around 1800. I was able to find the Sun in the telescope and then the clouds thinned enough toe see a nice display of sunspots. Then I thought I saw something on the limb at 12:30 - 1:30. The clouds were passing over the Sun making it hard to see and making it nearly impossible to use magnification greater than 50x. At 1805:39 there was enough darkening on the limb that I was sure I was seeing Venus and logged that as C1 although I figure that about 33% of the Venus' disk was already on the sun at that point. The clouds thickened and I didn't see the Sun any more from that location.
One of my objectives for this event was to time the contacts and the duration of the Black Drop Effect and see how my times differ from the generic NYC times published in Observer's Handbook 2012. I have been building a GPS-based occultation timer (a complete description should appear when the project is completed) that I had hoped to use for this purpose. On Thursday I got the minimum amount of code necessary to time this event assembled, and wired on an actuator switch to test it out. It was then that I discovered that I appear to have fried something in my hardware. It had previously successfully logging GPS data. The GPS appears to be working but the shield can't write to the data card so I was stuck with looking at my watch, which is set to an NTS clock, after the event and writing down the time. There is a lot of slop in that method but although I had my voice recorder with me I wasn't expecting to see anything so hadn't started it to get an 1800 time signal recorded to help reducing the recording. Anyway, I figured I could back out a rough time for C1 based on when I observed it and how much of Venus's disk was on the Sun's disk. First I calculated the time it takes for all of Venus to get onto the Su, the Ingress Duration time (C2-C1), then I multiplied that by the portion of Venus I estimated was on the Sun (33%) at the time I decided I really was seeing Venus to get my Delay Time.
| Predicted C1 | 18:03:57 |
|---|---|
| Predicted C2 | 18:21:26 |
| Ingress Duration | 00:17:39 |
| Delay Time | 00:05:49 |
Next I subtracted my Delay Time from my Observed C1 to get my Calculated C1.
| Observed C1 | 18:05:39 |
|---|---|
| Delay Time | 00:05:49 |
| Calculated C1 | 17:59:50 |
The Calculated C1 is 00:03:57 earlier than the Predicted C1. That is too big a value to be credible. The most likely explanation is that, not being able to see the portion of Venus that was not on the Sun's disk, I overestimated how much of Venus was on the Sun's disk. So, assuming that C1 actually occurred at the Predicted C1 time, I took my Observed C1 and subtracted the Predicted C1 to get the Difference in the two times and divided that Difference by the Ingress Duration time and determined that it is likely that only about 10% of Venus's disk was on the Sun's disk when I first saw it.
| Observeded C1 | 18:05:39 |
|---|---|
| Predicted C1 | 18:03:57 |
| Difference | 00:01:52 |
| Ingress Duration | 00:17:39 |
| % Venus on Sun | 10.6% |
A woman came past asking if I had seen another guy with a tripod. Then I got an email from Peter saying he had arrived at 1818 but it didn't say where he was. I emailed back asking where he was and shortly thereafter the woman came back to get me saying Peter had sent her to bring me to him. She said she was going to be very friendly with us since their observing equipment wasn't that great. It turns out they were observing through a Leitz surveyor's transit at 30x. Being a transit, which has to be able to resolve small graduations on stadia poles at a distance, it should have had very good resolution but did have a small exit pupil.
We were then set up on the very southern end of the park where the fishermen gather. They had some party support trucks there but security wasn't chasing anyone bold enough to cross through their barriers out of the area.
The Sun made fleeting appearances through the clouds for the next two hours or so. I found that if I followed the Crepuscular Rays of the Sun (the Fingers of God) up to their intersection in the clouds I could predict where the Sun was and the next time it started to appear had a much better chance of getting it in the eyepiece before it disappeared.
we found about a 10° disparity between the sun elevation data from our various IOS programs. LightTrac was saying it was down below 10° while SkySafari was showing it up over 20°. My experience with LightTrac has been that it is very accurate at displaying the current azimuth so I would expect it to exhibit the same degree of accuracy in it's altitude calculations. I have used SkySafari to successfully determine how far in azimuth Venus is from the Sun but don't think I have used it to get an absolute azimuth or to set an altitude. I did compare the map view from LightTrac to the reality and it seemed correct and the altitude listed in SkySafari was just too high for where the sun actually was. I have since checked in the Observer's Handbook 2012 and found that the Sun's elevation listed for NYC is C1: 24° and C2: 21° and we were over an hour past C2 when we made this discovery. So I will still be a LightTrac devotee, at least during the daytime when I am somewhere where there is Wi-Fi.
It was nearing sunset and it had started to rain when the Sun appeared again for a long enough time for more than one person to get a view through the eyepiece of one of the instruments. My view was poor at best since the 45° angled eyepiece had collected rain drops and I was having to look around and through both them and clouds, but I did see Venus again.
I had emailed Peter over the weekend suggesting that, since we already push the envelope by observing the planets at noon and try to observe the thinnest possible crescent Moons, we should start a branch of astronomy called Extreme Astronomy. I suggested that, in addition to the above, we could issue TotL certificates for things like the number of Messier objects observed while in the eye of a hurricane. I want to claim a certificate for observing a Transit of Venus in the rain.
