<p>This is a two part windscreen designed to minimize the effects of windshake on the telescope and to avoid the deterioration in image quality that wind would cause. The AAT is in a tall 6 story dome on a pretty exposed part of Siding Spring Mountain and so is likely more affected by wind gusts. Initially there were issues with the mount being too flexible and having an lower resonant frequency than expected, which was in the range that can be excited by wind buffeting (<a href="https://www.science.org.au/fellowship/fellows/biographical-memoirs/harry-clive-minnett-1917%E2%80%932003#8" rel="nofollow noreferrer">a mention</a> in the bio of Harry Minnett, a CSIRO engineer who worked on the AAT). This may have also lead to a more extensive windscreens but windscreens, particularly upper ones, are fairly common and exist at several other observatories. As an example, the <a href="http://www.ing.iac.es/Astronomy/telescopes/int/int_pointing_limits.html" rel="nofollow noreferrer">pointing limits</a> of the Isaac Newton Telescope page discusses the sky area that is available with and without lowering the upper windshield.</p>

CC BY-SA 4.0
2019-01-11T05:35:24.363Z
Thanks! Any thoughts on "...and how do the minimal aperture domes deal with temperature differences?"
uhoh
CC BY-SA 4.0
2019-01-11T06:19:33.130Z
The effects of the thermal environment on telescope seeing wasn't well known in the 1970's when the AAT was built which is why there is a library, offices and labs below the telescope floor... In more recent years, much more effort has been put into thermal management of enclosures. Better insulation in the dome floor and walls, elimination of heat sources in the dome (as much as possible) and better ventilation (see e.g. the large vents in this [Gemini pic](https://www.gemini.edu/gallery/media/gemini-north-telescope)) all help keep the dome air as close to ambient as possible.
astrosnapper
CC BY-SA 4.0
2019-01-11T05:30:08.390Z
2019-01-11T06:13:56.757Z
2019-01-11T06:13:56.757Z
astrosnapper
<p>Many older or "classic" telescope domes have a horizon-to-zenith opening in the dome, and this helps speed up the thermal equilibration between the inside and outside air, decreasing turbulence and its effects upon resolution.</p>

<p><a href="https://i.sstatic.net/ncIsj.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ncIsj.jpg" alt="enter image description here"></a></p>

<p><a href="https://commons.wikimedia.org/wiki/File:P200_Dome_Open.jpg" rel="nofollow noreferrer">Source</a></p>

<p><a href="https://i.sstatic.net/joYQP.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/joYQP.jpg" alt="enter image description here"></a></p>

<p><a href="https://gostargazing.co.uk/observatories-in-the-uk/" rel="nofollow noreferrer">Source</a></p>

<p>But the Anglo-Australian Telescope has second mechanism that tightly constrains the vertical extent of the opening as well, leaving just a tiny hole barely big enough for the telescope to see the sky.</p>

<p>What are the benefits of each of these, and how do the minimal aperture domes deal with temperature differences?</p>

<p><strong>below:</strong> Screen shot from the video <a href="https://www.youtube.com/watch?v=qOtkI4HYzTk" rel="nofollow noreferrer">A 2dF night at the Anglo-Australian Telescope</a> found <a href="https://angelrls.wordpress.com/2014/05/06/a-2df-night-at-the-aat/" rel="nofollow noreferrer">here</a>.</p>

<p><a href="https://i.sstatic.net/wKMix.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/wKMix.jpg" alt="enter image description here"></a></p>

<observatory><angular-resolution><weather><atmospheric-effects>
Why is the opening in the Anglo-Australian Telescope's dome so small?
uhoh
# Why is the opening in the Anglo-Australian Telescope's dome so small?

(Asked by: username_0 on 2019-01-11)

Many older or "classic" telescope domes have a horizon-to-zenith opening in the dome, and this helps speed up the thermal equilibration between the inside and outside air, decreasing turbulence and its effects upon resolution.

[![enter image description here](https://i.sstatic.net/ncIsj.jpg)](https://i.sstatic.net/ncIsj.jpg)

[Source](https://commons.wikimedia.org/wiki/File:P200_Dome_Open.jpg)

[![enter image description here](https://i.sstatic.net/joYQP.jpg)](https://i.sstatic.net/joYQP.jpg)

[Source](https://gostargazing.co.uk/observatories-in-the-uk/)

But the Anglo-Australian Telescope has second mechanism that tightly constrains the vertical extent of the opening as well, leaving just a tiny hole barely big enough for the telescope to see the sky.

What are the benefits of each of these, and how do the minimal aperture domes deal with temperature differences?

**below:** Screen shot from the video [A 2dF night at the Anglo-Australian Telescope](https://www.youtube.com/watch?v=qOtkI4HYzTk) found [here](https://angelrls.wordpress.com/2014/05/06/a-2df-night-at-the-aat/).

[![enter image description here](https://i.sstatic.net/wKMix.jpg)](https://i.sstatic.net/wKMix.jpg)

**Tags:** observatory, angular-resolution, weather, atmospheric-effects

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## 1 answers

### Answer by username_1 on 2019-01-11. Score: 4 | Accepted answer

This is a two part windscreen designed to minimize the effects of windshake on the telescope and to avoid the deterioration in image quality that wind would cause. The AAT is in a tall 6 story dome on a pretty exposed part of Siding Spring Mountain and so is likely more affected by wind gusts. Initially there were issues with the mount being too flexible and having an lower resonant frequency than expected, which was in the range that can be excited by wind buffeting ([a mention](https://www.science.org.au/fellowship/fellows/biographical-memoirs/harry-clive-minnett-1917%E2%80%932003#8) in the bio of Harry Minnett, a CSIRO engineer who worked on the AAT). This may have also lead to a more extensive windscreens but windscreens, particularly upper ones, are fairly common and exist at several other observatories. As an example, the [pointing limits](http://www.ing.iac.es/Astronomy/telescopes/int/int_pointing_limits.html) of the Isaac Newton Telescope page discusses the sky area that is available with and without lowering the upper windshield.

> **Comments:**
> **username_0**: Thanks! Any thoughts on "...and how do the minimal aperture domes deal with temperature differences?"  
> **username_1**: The effects of the thermal environment on telescope seeing wasn't well known in the 1970's when the AAT was built which is why there is a library, offices and labs below the telescope floor... In more recent years, much more effort has been put into thermal management of enclosures. Better insulation in the dome floor and walls, elimination of heat sources in the dome (as much as possible) and better ventilation (see e.g. the large vents in this [Gemini pic](https://www.gemini.edu/gallery/media/gemini-north-telescope)) all help keep the dome air as close to ambient as possible.  

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