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Nova2000

A weird question

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Hi. 

I don't know if this is the right forum. So please move it if necessary :)

As I've seen, more f ratio, slower the scope and more magnification. 

More distance the light travels the dimmer it gets. 

Does this apply to scopes in space? 

There is no atmosphere. So no changing in light if I'm not wrong. 

Does the air inside a scope have any play in this?. 

I am kind of unsure of this question now. 

To find magnification the formula is focal length divided by the eyepiece 

So what's the use of a bigger mirror? 

It only collects more light right? 

Raj:evil5:

 

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Hi. The light in space must get dimmer too with distance.It's a squared relationship. Three times the distance nine times dimmer-I'm sure I'll be corrected. 

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Bigger mirror equals more aperture.  more aperture equals more resolution and also more brightness at the same magnification compared with a smaller scope.

All scopes have a theoretical maximum magnification which Is about 30-50x aperture in Inches.  This applies anywhere but on Earth the atmosphere restricts this sometimes to 100x or so no matter what scope is used.

 

 

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For the avoidance of confusion, the distance travelled in the scope and the air in the scope have no impact on brightness of image. The main impact at this stage is the turbulence caused by air currents, that's why cooling (or rather thermal equilibrium) is so important.

Light rays entering a scope are generally considered to be parallel. However, over the the huge distances of space, they spread out so obey the inverse square law as Domstar said.

In a vacuum, a photon of light would continue uninterrupted effectively forever (as far as I'm aware!), but space is not empty, particularly within galaxies, there is dust and gas which can absorb photons, reducing the brightness of an object being viewed but sometimes these are re-emitted at different frequencies. It's a complex picture!

Aperture means more light, which means you can magnify small faint things by more whilst maintaining their surface brightness. Making objects larger helps our eye to perceive them more easily.

As Shane says, aperture also brings you more resolution, so if the atmospheric conditions allow it, a big dob will give fantastic planetary images, plenty of colour and detail.

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1 hour ago, Nova2000 said:

It only collects more light right?

That's the sole purpose of the  astronomical telescope, to gather light.
The more it gathers the  better, as your starting point, however limits are reached far before  the theoretical limits  are reached.

Under perfect conditions, dark sky, in a vacuum, my scope should provide 400x power (twice my aperture) however 200X (matching my aperture is a  far more practical  and reachable  target).
The disadvantages of the larger apertures would be size, weight, storage, cost, portability and reach ( will I reach the eyepiece without a step/ladder?)

But for better resolution and image scale, you need a bigger aperture.

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Really beyond my pay scale on this one, but here goes. A wavelength of light travelling from the stars and distant galaxies is effected by the distance it travels, causes change in its spectral make up, known as the Red Shift. Colour changes take place enabling a scale to be used, this helps scientists evaluate how far away they are and their general make up. Not forgetting that all of theses objects we observe, are constantly on the move at vast speeds. So yes, basically the farther away it is, the dimmer it gets.

A big mirror will provide more light grasp and enable, as a consequence of this, higher resolution than a smaller one. Magnification is a function of the focal ratio, a long focal length will provide greater magnification, but less field of view. Shorter focal lengths will give a much wider field of view, but at the expense of magnification. Long focal lengths are often preferred for Planetary, star splitting and other singular type observations. Wide field and subsequent lower magnification, is preferred for deep space observations and by imagers dealing with the photography side of the hobby.

Our atmosphere has a big effect on telescope observations, in space there is no effect on such as the Hubble, but here on Mother Earth, it depends on where you are, as to the clarity of the sky, this is why the worlds best telescopes are on Mountain tops at locations where the air is cleanest. The air where you observe will have some effect, as will the air column of air in your scopes tube, resulting in performance, such as clarity of vision, and the ability for you to obtain good magnification, this is why lower magnifications and better clarity of detail, with any given scope, is better than trying to achieve a much higher magnification and wondering why there is a blurred image :)

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5 minutes ago, glowjet said:

Really beyond my pay scale on this one, but here goes. A wavelength of light travelling from the stars and distant galaxies is effected by the distance it travels, causes change in its spectral make up, known as the Red Shift. Colour changes take place enabling a scale to be used, this helps scientists evaluate how far away they are and their general make up. Not forgetting that all of theses objects we observe, are constantly on the move at vast speeds. So yes, basically the farther away it is, the dimmer it gets.

Very definitely above my pay grade too ( ;) ), but my understanding is that red shift is not caused by distance per se, but by the speed with which distant objects are moving away from us, this speed increases with the distance they are from us.

The effect is similar to the Doppler affect heard when a vehicle with a siren approaches then passes you in the street. i.e. by the compression or stretching out of the light or sound waves relative to the observer which changes the perceived frequency.

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Most of the space is a vacuum right... 

So u don't feel it's necessary that light should get dimmer in space :)

Bug big puzzle of the cosmos 

But I feel gravity has a play also. Ie=gravitational lense. 

Just a additional question

the red/blue can it be observed in any way? 

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However, just because a star is relatively dim, doesn't necessarily mean its more distant. :BangHead:

Mike

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Yep-inverse squared relationship:sad:.I'm going to the bottom of the class.

While we are on the subject, is there any truth(plausibility) in the idea that if the universe wasn't expanding, the light from the stars would appear brighter- maybe much much brighter? I once read about somebody who hypothasized that the universe was expanding  before the Doppler effect was known, and his reasoning was that the sky at night would otherwise shine brightly. I'm afraid the details are lost in the fog that is my brain and I might have just dreamt it or heard about it from some guy in the pub. Anyway, I never could get my head around it so I thought I'd ask minds a lot sharper than my own.

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1 hour ago, Stu said:

Very definitely above my pay grade too ( ;) ), but my understanding is that red shift is not caused by distance per se, but by the speed with which distant objects are moving away from us, this speed increases with the distance they are from us.

The effect is similar to the Doppler affect heard when a vehicle with a siren approaches then passes you in the street. i.e. by the compression or stretching out of the light or sound waves relative to the observer which changes the perceived frequency.

Yes, Stu - light from a receding source like a galaxy is redshifted, and according to Hubble's Law, the shift is roughly proportional to the distance of the galaxy.

This has shown that remote galaxies are receding at more than the speed of light, but this does not contravene Special Relativity because it is not the object as such that is speeding away but it is rather space which is expanding at that rate.

Doug.

Edited by cloudsweeper
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13 minutes ago, Nova2000 said:

the red/blue can it be observed in any way? 

Using a spectrometer, you can separate the light into different wavelengths. Then you can check which wavelengths are missing, which correspond to elements that have absorbed a particular parcel of light. Results show the same pattern of missing wavelengths but moved along the scale due to the Doppler effect which shows that the stars are moving away from us.

2 questions- Do I understand this? and have any of you used a spectrometer in your astronomy experiences?

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8 minutes ago, domstar said:

Using a spectrometer, you can separate the light into different wavelengths. Then you can check which wavelengths are missing, which correspond to elements that have absorbed a particular parcel of light. Results show the same pattern of missing wavelengths but moved along the scale due to the Doppler effect which shows that the stars are moving away from us.

2 questions- Do I understand this? and have any of you used a spectrometer in your astronomy experiences?

Yes, you do understand it!  And blueshift occurs when the lines move the opposite way.  I believe this can happen when the edge of a galaxy is moving towards us due to rotation.  (From recollection - subject to confirmation!)

(I haven't used a spectrometer in astronomy, but have done so in analysing the spectra of triply-ionised Copper in a plasma from a very high current discharge.)

Doug.

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39 minutes ago, cloudsweeper said:

Yes, Stu - light from a receding source like a galaxy is redshifted, and according to Hubble's Law, the shift is roughly proportional to the distance of the galaxy.

This has shown that remote galaxies are receding at more than the speed of light, but this does not contravene Special Relativity because it is not the object as such that is speeding away but it is rather space which is expanding at that rate.

Doug.

Einstein stated that space is a consequence of mass, so space doesn't exist where there is no mass. If that's true, then for space to be expanding at a rate close to or faster than the speed of light, then mass must be coming into existance at an unbelievable rate. At any rate, the energy needed to create this phenomenon has to be greater than the total energy in the known universe. Where is the energy coming from?

If the Big Bang actually happened, what made it go BANG!? And, if the Big Bang actually happened, then the rate of expansion would at best remain constant and not increase. What we could be seeing is not the expansion of the universe, but rather the deceleration of the universe! The further we look, the further back in time we see, and we don't see anywhere near that kind of expansion in our local environment, because its not happening today.

The further we look, we see more and more of the same thing, galaxies galore! We are way past the point of the Big Bang, yet the boffins are desperate to hold onto this nonsensical hypothesis. 

I'm probably on my own in believing that the red shift over vast distances is largely the result of energy loss from originally high energy photons, as they interact with subatomic particles and other photons, as well as being severely affected by gravitation over such distances. Effectively, a high energy photon emitted from a star at the edge of the known universe, loses energy along its journey, and so is not the same photon that began the journey, and spectrally moves towards the red end of the spectrum.

Mike

 

 

 

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10 minutes ago, mikeDnight said:

Einstein stated that space is a consequence of mass, so space doesn't exist where there is no mass. If that's true, then for space to be expanding at a rate close to or faster than the speed of light, then mass must be coming into existance at an unbelievable rate. At any rate, the energy needed to create this phenomenon has to be greater than the total energy in the known universe. Where is the energy coming from?

If the Big Bang actually happened, what made it go BANG!? And, if the Big Bang actually happened, then the rate of expansion would at best remain constant and not increase. What we could be seeing is not the expansion of the universe, but rather the deceleration of the universe! The further we look, the further back in time we see, and we don't see anywhere near that kind of expansion in our local environment, because its not happening today.

The further we look, we see more and more of the same thing, galaxies galore! We are way past the point of the Big Bang, yet the boffins are desperate to hold onto this nonsensical hypothesis. 

I'm probably on my own in believing that the red shift over vast distances is largely the result of energy loss from originally high energy photons, as they interact with subatomic particles and other photons, as well as being severely affected by gravitation over such distances. Effectively, a high energy photon emitted from a star at the edge of the known universe, loses energy along its journey, and so is not the same photon that began the journey, and spectrally moves towards the red end of the spectrum.

Mike

 

Lots of profound questions/issues here!  Gravitational contraction was at one time expected I believe, but since it looks as though the reverse is taking place, Dark Energy has been suggested as an "explanation" but remains undiscovered and unexplained.  

Exciting times we're living in.  I eagerly await new developments!

Doug.

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29 minutes ago, mikeDnight said:

Einstein stated that space is a consequence of mass, so space doesn't exist where there is no mass. If that's true, then for space to be expanding at a rate close to or faster than the speed of light, then mass must be coming into existance at an unbelievable rate. At any rate, the energy needed to create this phenomenon has to be greater than the total energy in the known universe. Where is the energy coming from?

If the Big Bang actually happened, what made it go BANG!? And, if the Big Bang actually happened, then the rate of expansion would at best remain constant and not increase. What we could be seeing is not the expansion of the universe, but rather the deceleration of the universe! The further we look, the further back in time we see, and we don't see anywhere near that kind of expansion in our local environment, because its not happening today.

The further we look, we see more and more of the same thing, galaxies galore! We are way past the point of the Big Bang, yet the boffins are desperate to hold onto this nonsensical hypothesis. 

I'm probably on my own in believing that the red shift over vast distances is largely the result of energy loss from originally high energy photons, as they interact with subatomic particles and other photons, as well as being severely affected by gravitation over such distances. Effectively, a high energy photon emitted from a star at the edge of the known universe, loses energy along its journey, and so is not the same photon that began the journey, and spectrally moves towards the red end of the spectrum.

Mike

 

 

 

Mike, that is precisely how I view things! It has always seemed more logical that it was the reverse of the acceleration of universe. The further back you look, the closer you are in time to the Big Bang, therefore things are slowing down not speeding up!

I'm sure there is an argument against this involving someone who actually understands it, but I struggle to be persuaded away from this view.

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10 minutes ago, Stu said:

Mike, that is precisely how I view things! It has always seemed more logical that it was the reverse of the acceleration of universe. The further back you look, the closer you are in time to the Big Bang, therefore things are slowing down not speeding up!

I'm sure there is an argument against this involving someone who actually understands it, but I struggle to be persuaded away from this view.

I'll let you know if I ever get to understand it, Stu!  (Meanwhile, it's challenging and interesting trying to follow current theories of all kinds.)

Doug.

Edited by cloudsweeper
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The point Stu is that it is the fabric of space which is expanding, not the individual objects such as galaxies. They are carried along by this expansion. When you look back in time at distant objects they are seen from your reference frame and will be receding at the current rate of the expansion of the space fabric. This does not effect the value of the red shift. It is the Doppler effect on the light waves that change with distance. Also when you look at nearby objects they do not always show red shift. The Andromeda galaxy is a good example. It is in fact blue shifted. This is because at these distances gravity has a greater effect. That is why some day we will merge with Andromeda. Difficult concepts to get your head round I know, but the current theory for the evolution of the universe.

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29 minutes ago, laudropb said:

When you look back in time at distant objects they are seen from your reference frame and will be receding at the current rate of the expansion of the space fabric. This does not effect the value of the red shift. It is the Doppler effect on the light waves that change with distance.

Thanks John. I'm well aware that my half cocked 'theory' is unlikely to be right against the might of global science! ;)

However. I get everything you say apart from the bit I've quoted about. Surely we are still viewing them as they were in the past, rather than at their current rate of moving away from us, regardless of whether this is an actual movement or by the expansion of space time?

By the way, I'm not challenging, or saying any one is wrong; it is simply that this is one thing I've never got my head around.

Put simply, we see those distant galaxies accelerating away from us, but that is in the past. What are they doing now?

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45 minutes ago, Stu said:

 

Put simply, we see those distant galaxies accelerating away from us, but that is in the past. What are they doing now?

Accelerating away even faster, I guess!?

Doug.

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While we're at it, would anyone care to have a go at explaining the offside rule?

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10 hours ago, domstar said:

While we're at it, would anyone care to have a go at explaining the offside rule?

Depends on whether it relates to your team or the opposition!

Doug.

Or - offside is what happened just before the opposition scored.

Edited by cloudsweeper
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Yes Stu you are seeing them in the past. They may not even exist now. Red shift is a measure of distance not of time or the expansion of the universe. That is done by using the Hubble factor and the maths is way beyond me. Things have become even more complicated because it is now believed that the rate of expansion is increasing.

since neither of are astrophysics or cosmologists let's not worry about it too much and just enjoy gazing at the night sky.

All the best, John.

Edited by laudropb
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I enjoy seeing the look on people's face when I tell them that my telescopes are really 'Time-Machines.' They think I've lost my mind - until I explain what I mean about a light-year is a measure of time and space being used to reach one's eyes on Earth (for now, usually).

As for simple ways to learn about spectra and how it works, take a look here:

http://www.rspec-astro.com/star-analyser/

These are available from both the UK, and the USA.

http://www.starspectroscope.com/

A very interesting and educational pursuit - essentially seeing what stars are making from a vast distance in space & time.

Have fun -

Dave

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