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What telescopes can't see.

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#1 big eye

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Posted 24 November 2020 - 01:41 PM

This is one thing a telescope can not see from earth. A footprint on the moon why not. There are many reasons why this is impossible the first is a telescope would require 3,273,000 x magnification to start with next we would not be able to resolve the image due to the thick atmosphere of the earth and the fine harmonic vibration that the optical system would receive through natural and man made vibration that would render such an observation useless. So to conclude this fact if it was posable it would mean having an optical objective of 3000 feet in diameter and no atmosphere plus near to zero vibration.


 

#2 sg6

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Posted 24 November 2020 - 02:17 PM

They will still ask, however.

And a fair percentage will consider themselves as both astronomers and experts.


 

#3 JamesMStephens

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Posted 24 November 2020 - 02:22 PM

You estimated a magnification, I'll look at resolving power.  Look at a footprint--a foot, or 0.3 m (maybe width would be better)--at 384,000 km.  I get an angular size of 0.16 milliarcsconds (7.8*10-10 rad).  At 550 nm (visual band) wavelengths we'd need an aperture of about 700 meter!  Discounting all the other factors you mentioned.

 

Jim


Edited by JamesMStephens, 24 November 2020 - 02:40 PM.

 

#4 RalphMeisterTigerMan

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Posted 24 November 2020 - 02:22 PM

Optical telescopes are limited to the Visual portion of the Electro-magnetic spectrum. That means only between 4000 and 7000 angstroms or 400 to 700 nano-metres. So, nothing in the Infra-red and into the radio and beyond and nothing in the Ultra-violet or beyond into the X-ray and Gamma ray. Which translates into only what we humans can see which is just a teeny-tiny portion of the EM spectrum.

 

So, no American Flag or any other hardware left by the Apollo Astronauts on the moon, no "canals on Mars" because they just don't exist.

 

Also, since I am limiting this to Amateur telescopes, not much beyond the Kuiper belt when it comes to Asteroids and Comets and don't even think about mentioning the fictitious Nibiru or I'll get very mad. And you wouldn't like me when I get mad!!!

 

Larger dobsonian style reflectors in the 20 - 36" range will do very well with Galaxies and many other DSO's, especially under dark skies. Sure, under 20" to 10" can do Galaxies but they have to be the brighter ones limited to about 14th mag. or so depending on your seeing conditions.

 

You will be able to spot satellites in geosynchronos orbit and others. 

 

Clear skies!

RalphMeisterTigerMan


 

#5 big eye

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Posted 24 November 2020 - 02:35 PM

You estimated a magnification, I'll look at resolving power.  Look at a footprint--a foot, or 0.3 m (maybe width would be better)--at 384,000 km.  I get an angular size of 0.16 milliarcsconds (7.8*10-10 rad).  At 550 nm (visual band) wavelengths we'd need an aperture of about 700 m!  Discounting all the other factors you mentioned.

 

Jim

Hi, Jim, the aperture you have mentioned is that 700 meters. Ian.


 

#6 spereira

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Posted 24 November 2020 - 02:38 PM

Moving to Lunar Observing.

 

smp


 

#7 JamesMStephens

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Posted 24 November 2020 - 02:39 PM

Hi, Jim, the aperture you have mentioned is that 700 meters. Ian.

Yep.  I'll check the arithmetic.  Just set angle (radians) = (approx.) = wavelength/aperture


 

#8 big eye

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Posted 24 November 2020 - 02:46 PM

Yep.  I'll check the arithmetic.  Just set angle (radians) = (approx.) = wavelength/aperture

I wasn't too far of then maybe 2300 feet, not 3000 feet I have a bug in my calculator that is my calculating skills. Thanks, Jim.


 

#9 aeroman4907

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Posted 24 November 2020 - 03:18 PM

To put that in another perspective, if you utilized the same theoretical telescope and conditions, an object in the closest star system to us (Alpha Centauri at 4.37 light years) would need to be 32,366km in diameter to have the same angular dimension as the aforementioned footprint on the Moon.  Keeping in mind that Jupiter is 139,820 km in diameter, it would be impressive to be able to visually observe a planet in another system, albeit with almost no detail to speak of.


 

#10 big eye

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Posted 24 November 2020 - 04:39 PM

To put that in another perspective, if you utilized the same theoretical telescope and conditions, an object in the closest star system to us (Alpha Centauri at 4.37 light years) would need to be 32,366km in diameter to have the same angular dimension as the aforementioned footprint on the Moon.  Keeping in mind that Jupiter is 139,820 km in diameter, it would be impressive to be able to visually observe a planet in another system, albeit with almost no detail to speak of.

Yes, it would be impossible to see a planet even the size of Jupiter orbiting Alpha Centauri at the very best they are hoping one day to be able to see such a planet but only the size of a pinprick we must remember the fact that a planet is reflecting light with a dark background the footprint, however, is contrasting with its surroundings. Thank you for your detailed and interesting point. Ian.


 

#11 frank5817

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Posted 24 November 2020 - 06:40 PM

I am locking this forum thread it has drifted way off topic and this is a lunar observing thread. lock.gif


 


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