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[Centaur]

I’ve created Venus transit previews for 44 cities. The diagrams employ horizontal (alt-az) coordinates with zenith at the top. The apparent curved path of Venus is due to the Earth’s rotation. Unlike generic diagrams with straight paths utilizing geocentric equatorial coordinates, mine show how the transit will actually appear in the sky at specific locations.

The highly accurate Solex numerical integration software was utilized to determine the bodies’ relative positions at various times. Due to the parallax effect, event timings would vary among the locations even if adjusted to Universal Time.

The index to the 44 cities for my transit previews can be found at: www.CurtRenz.com/venustransit

[Centaur]

I added a 45th city upon request of someone from Wellington, New Zealand.

[Chicago Astronomer - Astro Joe]

Curt....

You should map these out and post a worldwide pushpin map.

[Centaur]

May 26, 2012 13:36:16 GMT -6 Chicago Astronomer - Astro Joe said:

Curt....

You should map these out and post a worldwide pushpin map.

Thanks for the sound idea, Joe. However the text format for city names has given my Venus transit index page a high Google browser priority. I'm afraid it's far too late to change that.

[Centaur]

Wow, the weather gods smiled upon Chicagoland. Perfectly clear skies here in the northwest suburbs. My timing predictions for first and second contact were confirmed. Science reigns supreme!

I joined a transit party at Harper College in Palatine. Besides an array of telescopes supplied by the college, an astronomy instructor brought his own nifty wooden triangular device designed solely for projecting an image of the Sun. Not only was it safe, but it allowed many to view simultaneously. There was a large and enthusiastic crowd.

My brother Kent and his girlfriend Kristy had planned to join Chicago Astronomer Patrick in Chicago's Horner Park. I'm sure they would have had an equally good time.

[patrickm]

Praise to Iron Man and the little baby Jesus! What a great afternoon/evening. Probably had 60-75 people but since it was just me I got only a couple of pics and no exact head count. Just steady and solid from 4:45 to 8:10 when we lost it in the trees.

More later. Gotta see Saturn, pack up, get home, eat dinner, collapse in a happy puddle of goo.

Whee!

[Paulie pchris00]

Jun 5, 2012 19:38:21 GMT -6 Centaur said:

My timing predictions for first and second contact were confirmed. Science reigns supreme!

Awesome, but unfortunately, not by me. All I wanted was to have ingress to myself, family, and friends, but things got really hectic at the contact times. For months I've been quoting your contact time down to the second to anybody who asked what time the transit started. Obviously, first contact in white light is impossible to gauge. I was staring intently at second contact, and got so caught up waiting for the black drop to "break" that I totally forgot about timing it.

It was windy, internet was down at Conway, and I missed timing the contact. Those aren't bad problems to have, and didn't even come close to hampering my excitement. What a day!

[tomlee]

Curt,

I see that you have already removed the 45 local transit pages. I am finding more uses of it now than before because only one friend needed the reference before but after my posting on Facebook there are questions and some can use illustration of the path. Please revive for a while. Thank you.

[Centaur]

Jun 6, 2012 9:40:38 GMT -6 tomlee said:

Curt,

I see that you have already removed the 45 local transit pages. I am finding more uses of it now than before because only one friend needed the reference before but after my posting on Facebook there are questions and some can use illustration of the path. Please revive for a while. Thank you.

Sorry, tomlee, but all 45 have been removed from my web host's server and deleted from my computer. If you reply with a specific location (longitude, latitude, altitude & time zone), I’ll create a single temporary diagram, and provide you with a temporary link good for a week.

[tomlee]

I should have mentioned it. I mostly refer to the general pattern so Chicago is good.

This bring up however another question while we are at it. We obviously don't see the whole pattern, right? so where is the ending point (at sunset time)? Oh, one more. Why is the path curve so severely? a link or two for some reading would be fine. I really have not much time to follow and research about this events.

Thank you so much!!

[patrickm]

Curt,
Why did you do that? One of the best features of the WWW is its function as a repository of knowledge and history. Server HD space is cheap. I don't even see Google caches of them, so maybe you have it set to not be crawled and cached, too? A shame that your hard work on those amazing graphics can never be seen by anyone again. Sad.

I had the Chicago one on my phone and can post that.


Curt, Kent and Christy were great. Kent knows much more about astronomy than I do and was fun to talk to. Their pinhole tube/periscope was also pretty cool! A funny guy. Thanks for sending them our way.

[Centaur]

You’re welcome, tomlee. Here is the reprised link to my transit diagram for Chicago at the Adler: www.CurtRenz.com/transit08 . I’ll leave it on the web indefinitely thanks to the goading of patrickm.

For Chicago observers the transit effectively ended at sunset. The continuation in my diagram is what would have been seen with a fictional X-ray vision while staring through solid earth. The curved path is due to the rotation of the Earth, which greatly affects the positioning within horizontal (alt-az) coordinates. When equatorial coordinates are employed, the path appears virtually straight.

[Centaur]

Jun 6, 2012 10:15:05 GMT -6 patrickm said:

Curt, Kent and Christy were great. Kent knows much more about astronomy than I do and was fun to talk to. Their pinhole tube/periscope was also pretty cool! A funny guy. Thanks for sending them our way.

Patrick, I’m so glad you could meet with Kent and Kristy. I took to astronomy at a very young age and was able to get all three of my younger brothers interested. They are all quite knowledgeable regarding astronomy and a great many other subjects. It’s marvelous that your transit party turned out so well.

[patrickm]

Jun 6, 2012 10:47:50 GMT -6 Centaur said:

The curved path is due to the rotation of the Earth, which greatly affects the positioning within horizontal (alt-az) coordinates. When equatorial coordinates are employed, the path appears virtually straight.

Uhhh, what? Wouldn't it transit the face of the sun as we see it in the same manner regardless? I get the part about looking through the Earth, but am confused.

[Centaur]

Jun 6, 2012 11:09:13 GMT -6 patrickm said:

Wouldn't it transit the face of the sun as we see it in the same manner regardless?

Not when you are rotating with the Earth while assuming that up toward the zenith remains a continuation of the line from Earth's center through your body.

Have you ever noticed how the Moon appears to tilt quite noticeably during the night, even though it is not really tilting much in inertial space?

[tomlee]

Thank you Curt.

Thank you Patrick.

[Paulie pchris00]

Basically it's field rotation in a non-equatorial mount. I can visualize it, but I don't know how to explain it.

When looking at the Sun naked eye (or assuming that I look at the Sun naked eye, because it's not safe to do so), I can roughly tell where north is. The Moon is easy, since it shows us more or less the same face. The phase also helps. The Sun, though, has no permanent markings to help determine north in a non-equatorial mount. I have to visualize how the Moon would be oriented if it were in the Sun's place instead. I don't have equatorial mounts, so I'm never quite sure where north is when looking at the Sun through any of my telescopes- proper eye safety precautions taken, of course. Looking at a near real time image from SDO helps. So does regular observing.

I can't remember how I was going to tie this to Patrick's question, so I'll just shut up now...

[erikruud]

If you took a sequence of photos during the transit with an alt-az mount, the apparent path of Venus would appear to be curved due to field rotation. A similar sequence taken using an EQ mount would show a straight line.

[erikruud]

By the way, should we start planning for the Transit of Mercury? It's less that four years away.

[Centaur]

Jun 6, 2012 13:07:13 GMT -6 erikruud said:

By the way, should we start planning for the Transit of Mercury? It's less that four years away.

Indeed, Erik, the next Mercury transit will occur on 2016 MAY 09. The entire transit will be visible from Chicago, if the weather gods smile upon us. Here's the link to my Chicago diagram for that event: www.CurtRenz.com/tran08

[Paulie pchris00]

Jun 6, 2012 12:21:08 GMT -6 erikruud said:

If you took a sequence of photos during the transit with an alt-az mount, the apparent path of Venus would appear to be curved due to field rotation. A similar sequence taken using an EQ mount would show a straight line.

That's what I was trying to say.

[Paulie pchris00]

Jun 6, 2012 13:53:00 GMT -6 Centaur said:

Jun 6, 2012 13:07:13 GMT -6 erikruud said:

By the way, should we start planning for the Transit of Mercury? It's less that four years away.

Indeed, Erik, the next Mercury transit will occur on 2016 MAY 09. The entire transit will be visible from Chicago, if the weather gods smile upon us. Here's the link to my Chicago diagram for that event: www.CurtRenz.com/tran08

I've been thinking about that for a few days now. Didn't know if we would be so lucky to be on the Sun facing side of the Earth.

It shouldn't have all the hype of the ToV, and starts at what normal thinking people should consider an ungodly hour. Do I hear a private CA session at an undisclosed location for this this? Let us have our geeky moments of yesterday without having to attend to the masses (not that I minded that)?

[Centaur]

Interestingly during the transit, I listened to two Harper College astronomy instructors supervising well separated viewing instruments. Both lectured to the crowd that Venus has 1/110th the diameter of the Sun, and the fact that Venus' image appeared larger was due to problems within the instruments.

I had to interrupt both instructors and explain to the groups that Venus appeared about 1/30th the diameter of the Sun because it was about 3.5 times closer to us than the Sun. That would make it appear about 3.5 times wider than it would have appeared if at the same distance as the Sun. Both instructors paused for a moment without a word as that sunk in, then quickly shifted to another matter related to the transit.

[Chicago Astronomer - Astro Joe]

If I were there...I would have stood up, pointed to Curt and announced..."What he said!"

[patrickm]

Jun 6, 2012 12:21:08 GMT -6 erikruud said:

If you took a sequence of photos during the transit with an alt-az mount, the apparent path of Venus would appear to be curved due to field rotation. A similar sequence taken using an EQ mount would show a straight line.

WHAT?!

I thought I was understanding until this.

Damn.
:/

[patrickm]

Jun 11, 2012 10:45:19 GMT -6 Centaur said:

Venus appeared about 1/30th the diameter of the Sun because it was about 3.5 times closer to us than the Sun. That would make it appear about 3.5 times wider than it would have appeared if at the same distance as the Sun.

This I get and I think I even got it right on transit day!

[Paulie pchris00]

Sounds like the Harper College profs don't observe the Sun much. If they did, they might have known that sunspots seen in smaller telescopes are roughly the size of Earth- and Venus. While in transit, Venus seemed to dwarf the planet sized sunspots.

Patrick, I'll try to answer you soon.

[Paulie pchris00]

Okay Patrick, this is the best I can explain it. But instead of the 2012 transit of Venus, let's use the 2016 transit of Mercury, visible entirely here in Chicagoland. First and second contact come early in the morning, not too long after sunrise, and third and fourth contact are in the early afternoon. Let's say you're going to observe this with your C9, and your old 4.5", which I believe was on an alt/az mount. Let's also say that you're going to be getting a continuous image through both telescopes. Assuming perfect polar alignment and tracking on both telescopes throughout our CGEM EQ mount, rotating along with the Earth, will show Mercury's transit as a straight line across the Sun. The alt/az mount, however, is not rotating with the Earth. It's tracking the Sun's rate of movement across the sky, but the field of view is not rotating, which will make it look as if north on the Sun is shifting. As the Sun rises, a continuous image of Mercury will show its path as a slow curve across the Sun. Around noon, however, as the Sun peeks in the sky, it will show Mercury curving sharply, and heading back down.

[patrickm]

Thanks for taking the time to do that, Paulie. I guess a better understanding of how the mounts are working would help. Gonna think on it some more and maybe try to find a visual, other than the one Curt had, to help.

You are the coolest, though.