How does diffraction affect telescope magnification?

[Emilyjoint]

Homework Statement

Vague class discussion. Stars are points and a telescope does not magnify them.
How then can more stars be seen with a telescope?

Homework Equations

I know magnification for a telescope is fo/fe but that is not much help

The Attempt at a Solution

Is it because diffraction makes bigger images?

 

[turbo]

Here's a hint. How does a telescope differ significantly from your naked eye?

 

[Emilyjoint]

The main thing about a telescope is that it magnifies.
That is what I think fo/ fe means

 

[turbo]

You are missing an important quality of telescopes.

 

[Emilyjoint]

I know that they cause diffraction which makes point sources larger. Is that what you mean.
Ps... I have looked on wiki for telescope magnification and could not find an explanation

 

[turbo]

I know that they cause diffraction which makes point sources larger. Is that what you mean.

Nope. You're over-thinking this. Go to the "telescope" thread and see if you can figure it out. I can't give you the answer (forum roles), but I can show you the way to good resources.

https://www.physicsforums.com/showthread.php?t=391086

 

[Emilyjoint]

I have just spent half an hour or so looking through that reference. It gives lots of advice about which telescope to buy...I already own a telescope (Meade)...but there is nothing to help me explain how I can see more stars !
"I am missing an important quality of telescopes"..."I am over-thinking this"... I don't get it... is there a straight forward answer ?
Do you have any other references that might help.
Is my diffraction idea wrong?

 

[turbo]

What are the critical physical qualities of the telescopes in that thread?

 

[Emilyjoint]

?
Thank you for your help

 

[turbo]

Maybe this would help.

http://www.telescope.com/Telescope-Buyers-Guide/p/99897.uts

 

[Emilyjoint]

I have a telescope and am not looking for advice about which telescope to buy.
I am no wiser about how it is that more stars can be seen through a telescope.
My first and only idea was that diffraction make bigger images and I will stick with that in our class discussion.

 

[turbo]

Don't do that emily, because it is wrong. Which telescopes will show you more stars than others and why?

 

[Emilyjoint]

I think I am correct when I say that diffraction makes stars look bigger. We have done calculations to show what is meant by 'resolution' which is to do with separating images.
I also know the equation for calculating angular width to find the size of a point source.
I do not know how it is wrong that this explains how stars can be seen !
If they look bigger because of diffraction it sounds right to me.

 

[turbo]

Again, what qualities would you want in a telescope to show you more and more (fainter and fainter) stars?

 

[Emilyjoint]

they should have bigger diffraction patterns... I don't know... that is why I came here... for help.

 

[turbo]

they should have bigger diffraction patterns... I don't know... that is why I came here... for help.

That's not the answer. I'm trying to throw resources at you, but I can't simply give you the answer. Forum rules, sorry.

 

[Emilyjoint]

But am I correct in saying that the diffraction pattern will be larger ?
If so I can use that in my discussion, something will come of it
I do not understand your 'rules'

 

[turbo]

Do you think huge professional telescopes have large diffraction patterns, and that's why they can show more stars?

 

[Emilyjoint]

you tell me ! It sounds reasonable to me !...if it works

 

[Jimmy Snyder]

Emily, you already know that the telescope doesn't make the star larger. What else does a telescope do. Something that's different from what your eyes do.

 

[Evo]

you tell me ! It sounds reasonable to me !...if it works

We don't give out answers here. We will guide you, but you have to do the work.

 

[Emilyjoint]

I am lost ! I think that the telescope does make the image of the star larger...isn't that what the diffraction pattern is.
That is the only thing that I can think of that makes it possible to see more stars.
I know that I have to do the work...I realize that no one here is going to give me an answer... I do not need to be told that ! is this a physics forum ?

 

[Emilyjoint]

no one has been able to give a better explanation than mine... am I wrong?

 

[micromass]

Why is it better to have large telescopes??

 

[Jimmy Snyder]

Emily, is there a book to go with your class? If so, does it have a discussion on how a telescope works? It does not make stars appear larger. At least let that soak in.

 

[Emilyjoint]

The textbooks I refer to are by Muncaster(my favourite) Nelkon (a bible) and Duncan.
All explain optics and telescopes in great detail.
I have no difficulty with that theory. I am beginning to feel a little stupid...am I missing something so obvious.
How is it that more stars can be seen through a telescope?

 

[micromass]

Again: why might I prefer a larger telescope to a smaller one?

 

[Jimmy Snyder]

It might help to consider that a telescope and an eye work in ways that are similar. What are some of the differences though? What happens to your eyes when you go from a bright room to a dark one?

 

[Emilyjoint]

My original question was "how/why can more stars be seen with a telescope", not why should I have a larger or smaller telescope !
I am still in the position that I can see more stars because diffraction makes the images larger, this is undoubtedly correct and I will use this argument in my presentation and see what reaction I get.
Thankyou foryour help

 

[micromass]

My original question was "how/why can more stars be seen with a telescope", not why should I have a larger or smaller telescope !

The thing is that your eyes ARE basically a very small telescope. A usual telescope is usually much larger than the human eye. Why is that you think??

 

[Emilyjoint]

"my eye is a small telecope"...thank you for your help.

 

[micromass]

OK, a final attempt, expanding on Jimmy's hint:

If I stand in a bright room and I turn off the light, then I can't see anything. However, a little while after, I can see quite well in the dark. What happened??

 

[micromass]

Let's say I'm in a dry african country and I want water. Suddenly it starts raining. What is the best strategy to catch a lot of water??

1) Standing outside, with your mouth open and pointed up to the sky.
2) Putting a bucket outside.
3) Building a large pool to catch water.

 

[Emilyjoint]

How does that help me in this problem/ discussion.
33 responses and I am no better off...not your fault...if you cannot help/give an answer just accept it and say so.
It is only a discussion question...at least I have some things to talk about.

 

[Jimmy Snyder]

Q: Stars are points and a telescope does not magnify them. How then can more stars be seen with a telescope?
A: It magnifies them.

This doesn't pass the giggle test. Are you absolutely certain that's what you want to go into the classroom with? I recommend you reread micromass's post #32 and tell us what you think about it.