<p>Here is part of a drawing from the Lowell Observatory booklet "100 Years of Good Seeing: The History of the 24-Inch Clark Telescope" (22 MB (i.e. large file warning) <a href="https://lowell.edu/wp-content/uploads/2014/08/100-Years-of-Good-Seeing-Clark-Telescope.pdf" rel="nofollow noreferrer">PDF</a>):</p>

<p><img src="https://i.sstatic.net/bHUs6.png" alt="Lower half of 24-inch refractor"></p>

<p>Dial 6 is the right ascension clock.
Without closely watching observatory staff operate the telescope, <em>the rest is speculation:</em></p>

<p>Being near dial 6 and linked by chains, knobs 4, 5, and 7 are probably for adjustments in right ascension.
Knob 5 could be a clutch to disengage for slewing and engage for sidereal tracking.</p>

<p>One of knobs 1-3 is for an iris near the objective, to limit chromatic aberration by reducing the aperture.
The other two knobs are probably for adjustments in declination; again one may be a clutch.</p>

CC BY-SA 4.0
2019-07-12T05:06:33.350Z
Thank you for tracking this down; what a beautiful instrument!
uhoh
CC BY-SA 4.0
2019-07-12T05:10:41.110Z
@uhoh You might enjoy this [14-minute video](https://www.youtube.com/watch?v=wRiKpX-Xy9A) about its recent restoration.
Mike G
CC BY-SA 4.0
2019-07-12T05:23:19.667Z
Okay I'll give it a watch now, thanks! btw I have just asked [What exactly is a Right Ascension clock and how was one (mounted on a telescope) used in practice, historically?](https://astronomy.stackexchange.com/q/32617/7982)
uhoh
CC BY-SA 4.0
2019-07-12T09:35:14.163Z
There's also this 141 page "coffee table book" mentioned in your linked [video](https://www.youtube.com/watch?v=wRiKpX-Xy9A) described at https://myastronomyshop.org/the-far-end-of-the-journey  which may have additional diagrams.
uhoh
CC BY-SA 4.0
2019-07-12T05:01:11.037Z
2019-07-12T05:04:06.080Z
2019-07-12T05:04:06.080Z
Mike G
<p>I contacted Dr. Danielle Adams, Deputy Director for Marketing and Communications at the Lowell Observatory. She was kind enough to reply, and generously provided the following (lightly edited for formatting):</p>

<blockquote>
  <p>I spoke with one of our senior educators about the Clark knobs. The numbers below correspond to the numbers in the image posted in <a href="https://astronomy.stackexchange.com/questions/32608/why-does-this-lowell-observatory-telescope-have-so-many-knobs-what-do-they-all">Why does this Lowell Observatory telescope have so many knobs? What do they all do?</a></p>
  
  <ol>
  <li>Slow motion control for adjusting Right Ascension (east-west movements) while the Right Ascension clutch (3) is locked down.</li>
  <li>Iris control that allows us to control the effective aperture of the telescope. There is an adjustable aperture that can be adjusted from 24" (wide open) to 6".</li>
  <li>Right Ascension clutch that when tightened prevents the telescope from being moved by pushing, allowing the telescope drive to operate.</li>
  <li>and 7. Slow motion controls for adjusting declination (north-south movements) while the Declination clutch (5) is locked down. The two controls are linked with bicycle chain so when one moves, so does the other. This allows operation of the control from either side of the viewing position.</li>
  <li>Declination clutch that when tightened prevents the telescope from being moved by pushing, allowing the telescope drive to operate.</li>
  <li>Sidereal clock that permits astronomers to point their telescopes to a given celestial object more easily.The sidereal day is about 4 minutes shorter than the 24 hour solar day. This is due to the fact that the Earth revolves around the Sun while it rotates about its axis.</li>
  <li>see (4)</li>
  </ol>
</blockquote>

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

CC BY-SA 4.0
2019-07-12T09:50:30.090Z
2019-07-12T09:50:30.090Z
uhoh
<p>The Fox News article <a href="https://www.foxnews.com/science/nasa-moon-landing-flagstaff-lunar-history" rel="nofollow noreferrer">Arizona city played critical role in moon exploration history</a> covers several interesting activities that took place in Arizona in preparation for the Apollo Moon landings.</p>

<p>It shows the telescope (shown below) and mentions that it was used to draw lunar maps.</p>

<p>There is more information about this telescope <a href="http://scopeviews.co.uk/LowellClarkRefractor.htm" rel="nofollow noreferrer">here</a> and <a href="https://lowell.edu/history/the-clark-refractor/" rel="nofollow noreferrer">here</a> as mentioned in <a href="https://astronomy.stackexchange.com/a/32609/7982">this answer</a>.</p>

<p><strong>Question:</strong> Why does this Lowell Observatory telescope have so many knobs? What do they all do? Is it possible to identify the function of all of the annotated controls and devices on this complicated-looking telescope?</p>

<p>I've added some numbers to facilitate discussion. There is also a chain going between the locations of #4 and #5, though I don't know exactly what it couples.</p>

<p><em>click images for full size viewing</em></p>

<p><img src="https://i.sstatic.net/2YnGs.jpg" alt="a Lowell Observatory telescope, annotated"></p>

<blockquote>
  <p><strong>above:</strong> Lowell Observatory telescope used by scientists who collaborated with artists to map out the moon for Apollo astronauts (Fox News) <a href="https://www.foxnews.com/science/nasa-moon-landing-flagstaff-lunar-history" rel="nofollow noreferrer">Source</a></p>
</blockquote>

<p><strong>below:</strong> Screenshot from July 9, 2019 Fox News video <a href="https://video.foxnews.com/v/6057102900001/#sp=show-clips" rel="nofollow noreferrer">NASA lunar legacy in the Arizona desert</a></p>

<p><img src="https://i.sstatic.net/Q3VOj.jpg" alt="a Lowell Observatory telescope"></p>

CC BY-SA 4.0
2019-07-11T03:01:53.250Z
companion question: [Which Lowell Observatory telescope is this? (used to draw Moon maps for the Apollo program)](https://astronomy.stackexchange.com/q/32607/7982) and possibly of interest: [What kind of reddish wood is it exactly that was historically used to line the inside of observatory copulas, in order to absorb moisture?](https://astronomy.stackexchange.com/q/23470/7982)
uhoh
CC BY-SA 4.0
2019-07-11T15:30:15.653Z
PHotos in the linked pages strongly suggest these are used for fine focus and alignment (tilt) of the secondary.  Maybe go buy the book advertised on those pages?
Carl Witthoft
CC BY-SA 4.0
2019-07-11T16:16:15.697Z
@CarlWitthoft refractors don't have secondaries, focus is done at the eyepiece, not the objective.
uhoh
CC BY-SA 4.0
2019-07-11T19:56:22.250Z
Well, whatever large optic is at the top of the tube is what's being adjusted
Carl Witthoft
<telescope><identify-this-object><observatory>
Why does this Lowell Observatory telescope have so many knobs? What do they all do?
uhoh
# Why does this Lowell Observatory telescope have so many knobs? What do they all do?

(Asked by: username_0 on 2019-07-11)

The Fox News article [Arizona city played critical role in moon exploration history](https://www.foxnews.com/science/nasa-moon-landing-flagstaff-lunar-history) covers several interesting activities that took place in Arizona in preparation for the Apollo Moon landings.

It shows the telescope (shown below) and mentions that it was used to draw lunar maps.

There is more information about this telescope [here](http://scopeviews.co.uk/LowellClarkRefractor.htm) and [here](https://lowell.edu/history/the-clark-refractor/) as mentioned in [this answer](https://astronomy.stackexchange.com/a/32609/7982).

**Question:** Why does this Lowell Observatory telescope have so many knobs? What do they all do? Is it possible to identify the function of all of the annotated controls and devices on this complicated-looking telescope?

I've added some numbers to facilitate discussion. There is also a chain going between the locations of #4 and #5, though I don't know exactly what it couples.

*click images for full size viewing*

![a Lowell Observatory telescope, annotated](https://i.sstatic.net/2YnGs.jpg)

> **above:** Lowell Observatory telescope used by scientists who collaborated with artists to map out the moon for Apollo astronauts (Fox News) [Source](https://www.foxnews.com/science/nasa-moon-landing-flagstaff-lunar-history)

**below:** Screenshot from July 9, 2019 Fox News video [NASA lunar legacy in the Arizona desert](https://video.foxnews.com/v/6057102900001/#sp=show-clips)

![a Lowell Observatory telescope](https://i.sstatic.net/Q3VOj.jpg)

**Tags:** telescope, identify-this-object, observatory

> **Comments:**
> **username_0**: companion question: [Which Lowell Observatory telescope is this? (used to draw Moon maps for the Apollo program)](https://astronomy.stackexchange.com/q/32607/7982) and possibly of interest: [What kind of reddish wood is it exactly that was historically used to line the inside of observatory copulas, in order to absorb moisture?](https://astronomy.stackexchange.com/q/23470/7982)  
> **username_1**: PHotos in the linked pages strongly suggest these are used for fine focus and alignment (tilt) of the secondary.  Maybe go buy the book advertised on those pages?  
> **username_0**: @username_1 refractors don't have secondaries, focus is done at the eyepiece, not the objective.  
> **username_1**: Well, whatever large optic is at the top of the tube is what's being adjusted  

---

## 2 answers

### Answer by username_2 on 2019-07-12. Score: 3 | Accepted answer

Here is part of a drawing from the Lowell Observatory booklet "100 Years of Good Seeing: The History of the 24-Inch Clark Telescope" (22 MB (i.e. large file warning) [PDF](https://lowell.edu/wp-content/uploads/2014/08/100-Years-of-Good-Seeing-Clark-Telescope.pdf)):

![Lower half of 24-inch refractor](https://i.sstatic.net/bHUs6.png)

Dial 6 is the right ascension clock.
Without closely watching observatory staff operate the telescope, *the rest is speculation:*

Being near dial 6 and linked by chains, knobs 4, 5, and 7 are probably for adjustments in right ascension.
Knob 5 could be a clutch to disengage for slewing and engage for sidereal tracking.

One of knobs 1-3 is for an iris near the objective, to limit chromatic aberration by reducing the aperture.
The other two knobs are probably for adjustments in declination; again one may be a clutch.

> **Comments:**
> **username_0**: Thank you for tracking this down; what a beautiful instrument!  
> **username_2**: @username_0 You might enjoy this [14-minute video](https://www.youtube.com/watch?v=wRiKpX-Xy9A) about its recent restoration.  
> **username_0**: Okay I'll give it a watch now, thanks! btw I have just asked [What exactly is a Right Ascension clock and how was one (mounted on a telescope) used in practice, historically?](https://astronomy.stackexchange.com/q/32617/7982)  
> **username_0**: There's also this 141 page "coffee table book" mentioned in your linked [video](https://www.youtube.com/watch?v=wRiKpX-Xy9A) described at https://myastronomyshop.org/the-far-end-of-the-journey  which may have additional diagrams.  

---

### Answer by username_0 on 2019-07-12. Score: 10

I contacted Dr. Danielle Adams, Deputy Director for Marketing and Communications at the Lowell Observatory. She was kind enough to reply, and generously provided the following (lightly edited for formatting):

> I spoke with one of our senior educators about the Clark knobs. The numbers below correspond to the numbers in the image posted in [Why does this Lowell Observatory telescope have so many knobs? What do they all do?](https://astronomy.stackexchange.com/questions/32608/why-does-this-lowell-observatory-telescope-have-so-many-knobs-what-do-they-all)
>
> 1. Slow motion control for adjusting Right Ascension (east-west movements) while the Right Ascension clutch (3) is locked down.
> 2. Iris control that allows us to control the effective aperture of the telescope. There is an adjustable aperture that can be adjusted from 24" (wide open) to 6".
> 3. Right Ascension clutch that when tightened prevents the telescope from being moved by pushing, allowing the telescope drive to operate.
> 4. and 7. Slow motion controls for adjusting declination (north-south movements) while the Declination clutch (5) is locked down. The two controls are linked with bicycle chain so when one moves, so does the other. This allows operation of the control from either side of the viewing position.
> 5. Declination clutch that when tightened prevents the telescope from being moved by pushing, allowing the telescope drive to operate.
> 6. Sidereal clock that permits astronomers to point their telescopes to a given celestial object more easily.The sidereal day is about 4 minutes shorter than the 24 hour solar day. This is due to the fact that the Earth revolves around the Sun while it rotates about its axis.
> 7. see (4)

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


---

