<p>This is a cross-post of <a href="https://space.stackexchange.com/questions/66659">https://space.stackexchange.com/questions/66659</a></p>
<p>According to Wikipedia, the proposed Lunar Radio-telescope design is a fixed parabolic dish. <a href="https://en.wikipedia.org/wiki/Lunar_Crater_Radio_Telescope#/media/File:Niac2020_bandyopadhyay.jpg" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Lunar_Crater_Radio_Telescope#/media/File:Niac2020_bandyopadhyay.jpg</a></p>
<p>As a rule, fixed radio-telescope dishes are spherical and are aimed by changing the antenna location. Aim-able radio-telescopes are parabolic and are aimed to place the axis on the object of regard.</p>
<p>If parabolic dishes are  used off-axis, caustic aberrations limit their resolutions. Spherical dishes are never off-axis because they have no axis.</p>
<p>if Earth-bound fixed-dish radio-telescopes are all spherical, why would a Lunar fixed-dish radio-telescope be parabolic ?</p>

CC BY-SA 4.0
2024-08-19T20:44:19.443Z
They answer the question in the original post, the telescope is not meant to be parabolic any way.
Polaris5744
CC BY-SA 4.0
2024-08-19T23:10:34.447Z
@Polaris5744 ... The Wikipedia page describes the dish as parabolic, as do some NASA documents. Although, there is also reference to the dish being a "spherical cap" reflector.
Woody
CC BY-SA 4.0
2024-08-20T07:07:15.123Z
I’m voting to close this question because it's not a bad question, but based on an error in Wikipedia and in the media, and already answered on Space
James K
CC BY-SA 4.0
2024-08-20T14:33:22.960Z
@JamesK ... Nasa documents contain references to both parabolic and spherical designs. Apparently both were considered. The lunar telescope is very long wavelength compared with terrestrial radio telescopes so that may play a part. What is the trade-off between the designs for this application?
Woody
CC BY-SA 4.0
2024-08-21T00:22:10.907Z
Woody, you should edit your question to make it about trade-off between designs. :-)
Chappo Hasn't Forgotten
CC BY-SA 4.0
2024-08-21T00:28:23.273Z
@ChappoHasn'tForgotten ... you're right. Its on the to-do list
Woody
<space-telescope><radio-telescope>
Why is the proposed lunar radiotelescope parabolic rather than spherical like Arecibo and FAST
Woody
# Why is the proposed lunar radiotelescope parabolic rather than spherical like Arecibo and FAST

(Asked by: username_0 on 2024-08-19)

This is a cross-post of <https://space.stackexchange.com/questions/66659>

According to Wikipedia, the proposed Lunar Radio-telescope design is a fixed parabolic dish. <https://en.wikipedia.org/wiki/Lunar_Crater_Radio_Telescope#/media/File:Niac2020_bandyopadhyay.jpg>

As a rule, fixed radio-telescope dishes are spherical and are aimed by changing the antenna location. Aim-able radio-telescopes are parabolic and are aimed to place the axis on the object of regard.

If parabolic dishes are used off-axis, caustic aberrations limit their resolutions. Spherical dishes are never off-axis because they have no axis.

if Earth-bound fixed-dish radio-telescopes are all spherical, why would a Lunar fixed-dish radio-telescope be parabolic ?

**Tags:** space-telescope, radio-telescope
> **Comments:**
> **username_1**: They answer the question in the original post, the telescope is not meant to be parabolic any way.  
> **username_0**: @Polaris5744 ... The Wikipedia page describes the dish as parabolic, as do some NASA documents. Although, there is also reference to the dish being a "spherical cap" reflector.  
> **username_2**: I’m voting to close this question because it's not a bad question, but based on an error in Wikipedia and in the media, and already answered on Space  
> **username_0**: @JamesK ... Nasa documents contain references to both parabolic and spherical designs. Apparently both were considered. The lunar telescope is very long wavelength compared with terrestrial radio telescopes so that may play a part. What is the trade-off between the designs for this application?  
> **username_3**: Woody, you should edit your question to make it about trade-off between designs. :-)  
> **username_0**: @ChappoHasn'tForgotten ... you're right. Its on the to-do list  

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