# How does diffraction affect telescope magnification?

• Emilyjoint
In summary, the discussion was about homework equations and stars. The class was discussing how more stars can be seen with a telescope. Emily thinks that diffraction makes stars look bigger. She is lost and doesn't understand why her diffraction theory is better than others. The class has no answer for her and she becomes frustrated.
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?

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

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

You are missing an important quality of telescopes.

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

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Emilyjoint said:
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.

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?

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

?

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.

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

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.

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

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

Emilyjoint said:
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.

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'

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

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

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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.

Emilyjoint said:
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.

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 ?

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

Why is it better to have large telescopes??

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.

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?

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

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?

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.

Emilyjoint said:
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??

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

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??

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.

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.

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.

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