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michel123456

Question related to Bxl's observatory instrument

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The image below comes from the official site of the Royal Observatory of Belgium (history in French only), labelled by me. There is a device (2 parallel wires? tubes?) coming from building A and running through B & C until building D. Has anyone an idea of what instrument it was?

1693094145_BXLobservatory.thumb.jpg.909159bee203ebcce346f57b818c5de2.jpg

Notes:

1. the device does not exist today. The buildings remained.

2. I have no idea of the date of the picture.

3. It is a genuine question, I have no clue.

the link to the observatory site :https://www.astro.oma.be/en/

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Fascinating puzzle! I have no idea. Reading through the history, the only thing I can guess it might be is for seismology. 

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What is the orientation of the system?

Google maps suggests that it is N-S, which means it's possible that this was a transit telescope. At the Naval Observatory was had these - you can measure when a star passes by the N-S line, and use that to make star charts for celestial navigation. There are buildings built some distance away so that the telescope can sight in on a target known to be on the N-S line and calibrate the scope. At USNO the targets have been demolished, but the transit telescope building foundations remain, and there are still some trees used as windbreaks to make sure the air would be still for sighting in on the targets.

You can see the foundations on the center line, one just to the east and one just to the west of center. The remaining rows of trees are just to the northwest (aligned with the foundation on the left of center)

https://www.google.com/maps/place/United+States+Naval+Observatory/@38.9215924,-77.0679255,834m/data=!3m1!1e3!4m5!3m4!1s0x89b7b62f93f61443:0xeba717baca31d77d!8m2!3d38.9216743!4d-77.0668837

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Posted (edited)
49 minutes ago, swansont said:

Google maps suggests that it is N-S, which means it's possible that this was a transit telescope

Like the suggestion, but looking at the photograph the domes are all off the axis of the linear structure.
I'm not sure what use the linear structure would be to targetting either.

There is a similar linear structure still there at the Royal Observatory, Greenwich, outside Flamsteed House, but it is just a covered way.
There are no such structures at the Observatories in Edinburgh or Dundee.

 

1 hour ago, michel123456 said:

The image below comes from the official site of the Royal Observatory of Belgium (history in French only), labelled by me. There is a device (2 parallel wires? tubes?) coming from building A and running through B & C until building D. Has anyone an idea of what instrument it was?

Michel I have not good ideas, but I have a suggestion.

The observatory has a 'contact us' tab on their website.

Why not ask them by email?

Note your picture refers to the new site after the relocation in the 1880s, the original observatory was elsewhere. Google has a picture of this, different from yours.

Edited by studiot

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45 minutes ago, studiot said:

Note your picture refers to the new site after the relocation in the 1880s, the original observatory was elsewhere. Google has a picture of this, different from yours.

Yes. The ancient observatory  (1826) is closer to downtown (and does not look like an observatory at all). The actual observatory was created in 1890. I suspect the picture is from 1950's but it is a simple guess.

 

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1 hour ago, studiot said:

Like the suggestion, but looking at the photograph the domes are all off the axis of the linear structure.
I'm not sure what use the linear structure would be to targetting either.

The USNO structures weren't domes, since they didn't need to rotate laterally (only elevation changes). There's a solid black line in that building on the right that could be where the telescope can view. Can't see the other side because of the "B"

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6 minutes ago, swansont said:

The USNO structures weren't domes, since they didn't need to rotate laterally (only elevation changes). There's a solid black line in that building on the right that could be where the telescope can view. Can't see the other side because of the "B"

1948918624_ScreenShot04-20-20at08_52PM.thumb.JPG.6aa62544209fa9033ad856746ba811ef.JPG

 

This is a closer view from Google Earth (3D buildings activated). The fondations of the pillars are slightly visible (in red circles). If I understand your explanation, the telescope was located in the building in the red rectangle. There seems to be 2 openings (sliding roof).

So the "wires" are only for visual alignment?

 

And yes it seems to be exactly on N-S axis.

224879429_ScreenShot04-20-20at04_54PM.thumb.JPG.77d374e3a5ad1a6dff463f94abf00aab.JPG

1 hour ago, studiot said:

Why not ask them by email?

Done.

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12 minutes ago, michel123456 said:

So the "wires" are only for visual alignment?

Tow possibilities I can think of: either they are hollow tubes and you did sighting down the tube to the calibration target (therefore no wind to cause distortion), or that structure was a framework that allowed one to hang a wind-block material to do the job that the trees did at USNO.

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Posted (edited)

I found some history.

The main astronomic activity around 1880 - 1900 appears to have been in solar spectroscopy.
They nearly (but did not pursue it) discover the Zeeman effect.

This article has some possibly useful references at the end.

 

http://adsabs.harvard.edu/full/1995ASPC...81....3S

54 minutes ago, michel123456 said:

Done.

 

Edited by studiot

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And here the (translated by me) answer from the Observatory: In the text below, the word "Mire" means "target" (Retroreflector if I understand correctly)

Quote

Hello,

We have received your message and have sent your question to the person in charge of our archives. As she was out of work this month, there was a short delay before she could send me the requested information. We apologize for the delay it caused to respond to you.

The photo that you attached presented a structure of tubes which were installed in the beginning of the 20th century (they were there in 1908, as you can see on the photo attached 1908_12.jpg), but which did not last long (at plus a few years).

These tubes connected the Meridian Room (building B), to the various small buildings called North Mire (A), Central Mire (C) and South Mire (D). The Meridian Hall was historically a center of observation of the passage of the stars to the meridian of Uccle (the meridian is a fictitious north-south line from which one can in particular make astronomical measurements and determine the local time (before time zone system, then the advent of atomic clocks).

To be able to calibrate the bezel of the meridian, we use a system of mirrors hung on the north and south sights (see the location of these mirrors on the image IMG_8607.jpg). (Hence the name "Mire" given to the buildings) The central Mire does not have mirrors, but lets light get through. A line of light is emitted from the Meridian Room towards the sights which reflect it thanks to the mirrors towards the Meridian Room.

However, problems with air convection disrupt the spread of light and nighttime observations. We then decided to install these tubes to improve the calibration and eliminate the effect of convection. However, this installation did not give the expected improvement. We then simply removed these tubes after several years of service.

Do not hesitate to come back to us if you have any other questions regarding my explanation.

Best regards,

1908_12.thumb.jpg.8541b5797b36e1c29d1e211213e8311a.jpg

 

IMG_8607.thumb.JPG.a26684940a0f0e614405c2b13a853690.JPG

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2 hours ago, michel123456 said:

And here the (translated by me) answer from the Observatory: In the text below, the word "Mire" means "target" (Retroreflector if I understand correctly)

Thank you +1

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The meridian line means it's a transit measurement. So, basically as I had guessed.

Interesting find!

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1 hour ago, swansont said:

The meridian line means it's a transit measurement. So, basically as I had guessed.

Interesting find!

Yes, your guess was correct. You are not so bad after all.

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