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Stellarium, Need Help Plz, 1761/69 Venus Transits

Planetarium Software Solar
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11 replies to this topic

#1 CreAtivSpelErr

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Posted 02 March 2024 - 05:47 PM

I'm using Stellarium to do a presentation about the ill-fated trip of Guillaume Le Gentil to measure the transit of venus in 1761 and 1769.

 

He was at Puducherry, India for both transits.  

For the 1761 I use the following script commands which bring me to the beginning of the transit at the correct location and everything in Stellarium looks just right.  

 

core.setObserverLocation(79.80, 11.95, 100, 1, " Puducherry, India", "Earth");
core.setDate("1761:06:06T2:00:00");

core.selectObjectByName("Sun");
StelMovementMgr.setFlagTracking(true);

 

But when I try to do the 1769 transit using these script commands...

 

core.setObserverLocation(79.80, 11.95, 100, 1, " Puducherry, India", "Earth");
core.setDate("1769:06:03T19:00:00");

core.selectObjectByName("Sun");

StelMovementMgr.setFlagTracking(true);

 

It is at about local midnight, which is a terrible time to observe a transit, generally speaking.  If I turn off landscapes and look straight down, the transit is indeed happening at the specified time, so the date and time are not wrong.  It would seem that the location is wrong, but it's the same as what I used for the earlier transit.  And it is historically documented that Le Gentil was in Puducherry, India for both transits.  So something is off, but I can't figure out what.  Any ideas?


Edited by CreAtivSpelErr, 02 March 2024 - 06:54 PM.


#2 michael8554

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Posted 03 March 2024 - 05:02 AM

I agree with your settings.

 

But I don't believe you have described what is wrong with what you are seeing.

 

Where do you see Venus to be in relation to the Sun at 19:00 GMT ?



#3 gzotti

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Posted 03 March 2024 - 08:09 AM

The sun rose at 5:34 local mean time. Venus was already in transit, 4th contact around 7:00:00 LMT. Do you have a report that he observed the second transit completely?



#4 gzotti

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Posted 03 March 2024 - 08:21 AM

Ah no, he was clouded out at the second attempt. I have not seen a discussion that would have mentioned this to have been early-morning.



#5 gmiller123456

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Posted 03 March 2024 - 10:42 AM

Is the API expecing the lat,lon in radians?

#6 CreAtivSpelErr

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Posted 03 March 2024 - 11:58 AM

The problem is that it is happening at local midnight and the sun is down in the dirt, only visible if the landscape is turned off.  Is that problem being replicated by other users?

 

If core.setDate("1769:06:03T19:00:00"); is coming up mid-transit, you might check if the sun is scaled to 4x.  I made that mistake recently but 

 

When I enter 

core.setObserverLocation(79.80, 11.95, 100, 1, " Puducherry, India", "Earth");

then check the location panel, it shows a red arrow at the correct location, and it works fine for the 1761 transit.



#7 michael8554

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Posted 03 March 2024 - 12:44 PM

I don't understand.

 

If the sun is below the local landscape horizon, then you'll have to turn off the landscape to see it.

 

On my planetarium, the sun at location Puducherry is below my local  landscape horizon at 1900, approx start of 1st Contact, but above the true horizon.



#8 CreAtivSpelErr

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Posted 03 March 2024 - 01:22 PM

transit

 

Here is a wide fov with landscape off.  If I zoom in, I can confirm that this is just before first contact.  

An Azimuthal grid put it a 55 degrees below the horizon.  



#9 gzotti

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Posted 03 March 2024 - 01:51 PM

Not sure what you expect. If you set 19:00 UT, it is around midnight in India. The Sun is commonly invisible around that time. What, exactly, do you doubt? Le Gentil had a chance to see just the end of this transit.

I like the solar eclipse just hours after that transit... :-)



#10 CreAtivSpelErr

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Posted 03 March 2024 - 01:55 PM

I'm with you.  Part of why it took me a while to get to that point is that I'm a bit new to Stellarium and it took me a while to get the UTC vs local timezones figured out.  

 

Like you said, the UTC time for the transit is listed as roughly 19:00 to 1:30.  With india at +5.5hr, that puts the sun where the planetarium software shows it, which is to say, sun rise happening when the transit is just about over. 

 

I thought that the transit expeditions of that time were trying to measure the duration of the transit, which requires seeing the beginning and the end, so I didn't think Le Gentil would hang around for 8 years knowing he could only see the end of the second transit. 

 

I know there are calculations that can be done using transit duration, but maybe just the end time was enough to be useful and that's all he was planning on taking.  


Edited by CreAtivSpelErr, 03 March 2024 - 02:01 PM.


#11 gzotti

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Posted 03 March 2024 - 02:56 PM

I cannot say whether Le Gentil knew he had no chance to see the whole second transit. Maybe the location's coordinates were so well-determined already and that, together with accurate timing, would have made the exit observation scientifically valuable to justify his stay. He wanted to go to Manila, but was not allowed. Also from there he would have missed almost half of it.



#12 Fabricius

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Posted 03 March 2024 - 04:09 PM

Like you said, the UTC time for the transit is listed as roughly 19:00 to 1:30.  With india at +5.5hr, that puts the sun where the planetarium software shows it, which is to say, sun rise happening when the transit is just about over.

The 1769 transit was not over yet at sunrise.

The total duration of the transit was 5h20m in Pondicherry (first ingress 19.15 UT, when the sun and Venus were below horizon).

According to the paper "Indian astronomy and the transits of Venus - 1. The early observations" (link), page 270,  the transit ended at 01.35 UT in India, though the exact location is not specified in the table.

According to planetarium software Cartes du Ciel, sunrise was at 00.15 UT and the Venus transit ended at 1.36 UT, both in Pondicherry.

The final stage of the transit has been observed early in the morning by observers in Dinapoor and Phesabad, India.

 

 


Edited by Fabricius, 03 March 2024 - 04:13 PM.



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