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Semirhage
2001-Dec-18, 05:20 PM
As I understand it, light travels at a finite speed, and the light that we are receiving now is actually old light (that is, light 'reflecting' old events). In the case of seeing things 10 billion light years away, we are seeing those things as they were 10 billion years ago.

What I don't understand is where Hubble, etc. comes into play? I understand that we can only see this distant galaxies using Hubble. So what's going on here - is it just that Hubble can make out the light that is there for all of us to see if we had the proper eyes, or is there some other principle at work? I can understand this stuff on the small (relatively) scale of the sun and how what I see when I look up is 8-minute (approx.) old light. But if I turned a telescope on the sun (assuming my eyes were protected), would I see the sun as it was LESS THAN 8 minutes ago, or would I simply be able to make out more detail in the 8-minute old light?

That is, what precisely is Hubble doing that allows it to see 'back in time' more than I see back in time with my eyes, if it does in fact do so?

If this still doesn't make sense, I guess I'm just feeling like it seems like Hubble is somehow acting to zoom in on the past or something, which seems to me weird and not right. So I must be misunderstanding something.

Also, could a sufficiently-built telescope actually look back to the original expansion of the Big Bang itself? To "before" Planke Time?

Valiant Dancer
2001-Dec-18, 05:45 PM
On 2001-12-18 12:20, Semirhage wrote:
As I understand it, light travels at a finite speed, and the light that we are receiving now is actually old light (that is, light 'reflecting' old events). In the case of seeing things 10 billion light years away, we are seeing those things as they were 10 billion years ago.

What I don't understand is where Hubble, etc. comes into play? I understand that we can only see this distant galaxies using Hubble. So what's going on here - is it just that Hubble can make out the light that is there for all of us to see if we had the proper eyes, or is there some other principle at work? I can understand this stuff on the small (relatively) scale of the sun and how what I see when I look up is 8-minute (approx.) old light. But if I turned a telescope on the sun (assuming my eyes were protected), would I see the sun as it was LESS THAN 8 minutes ago, or would I simply be able to make out more detail in the 8-minute old light?

That is, what precisely is Hubble doing that allows it to see 'back in time' more than I see back in time with my eyes, if it does in fact do so?

If this still doesn't make sense, I guess I'm just feeling like it seems like Hubble is somehow acting to zoom in on the past or something, which seems to me weird and not right. So I must be misunderstanding something.

Also, could a sufficiently-built telescope actually look back to the original expansion of the Big Bang itself? To "before" Planke Time?


You are correct about the nature of light from distant galaxies being in transit a long time. In short, Hubble is able to magnify the light from distant places making them visible to observers. If you turned a telescope on the sun (not a good idea) you would be able to see (assuming you aren't blind by this point) a more detailed view of the surface of the sun as it existed eight minutes ago. Telescopes only make the images of far away things larger, not make the light younger. In addition, Hubble doesn't have to worry about the distortions that the earth's atmosphere cause in surface based observatories.


_________________
Valiant Dancer

<font size=-1>[ This Message was edited by: Valiant Dancer on 2001-12-18 12:51 ]</font>

ToSeek
2001-Dec-18, 06:14 PM
On 2001-12-18 12:45, Valiant Dancer wrote:
Telescopes only make the images of far away things larger, not make the light younger.


Most importantly, telescopes are capable of gathering more light than our eyes and are thus able to image objects too far away and therefore too dim for us to see with our naked eye.

Hale_Bopp
2001-Dec-18, 07:53 PM
Telescopes also have the advantage of being able to take a timed exposure. Our eyes don't do that. The "exposure time" of your eye would be on the order of hundreths of a second or so. Therefore, your cannot collect enough light to see dim objects.

Hubble collects light over a much larger surface. It can also take exposures that are hours or even days long. The longer the exposure, the brighter the image becomes since more light can build up (there is a limit to this process...eventually the Hubble camera will become saturated which is similar to overexposing a film picture).

Also, having a larger collecting area allows a smaller details to be seen in the image (or alternately, having two or more telescope placed a distance away from each other and doing interferometry can also increase the resolution).

And of course, Hubble is above the Earth's atmosphere as someone mentioned. It does not have to deal with the distortion which limits even the best ground based telescopes to about 1 arc second resolution on a good night (unless you use adaptive optics). You also don't have to worry about pollution, clouds, and light pollution.

The big problem is that there is only one of them and it's pretty darn expensive to make another! The NGST (Next Generation Space Telescope) has a projected launch date of late this decade and will have a larger mirror and operate in the infrared to see highly red shifted objects.

In the mean time, there is a proposal for a small infrared telescope called PRIME (Primordial Explorer) to be launched in 2005 I think. It would conduct an infrared survey of the sky, similar to the Sloan Digital Sky Survey and would be used for target selection for the NGST.

Rob

Rob

Hale_Bopp
2001-Dec-18, 07:54 PM
Telescopes also have the advantage of being able to take a timed exposure. Our eyes don't do that. The "exposure time" of your eye would be on the order of hundreths of a second or so. Therefore, your cannot collect enough light to see dim objects.

Hubble collects light over a much larger surface. It can also take exposures that are hours or even days long. The longer the exposure, the brighter the image becomes since more light can build up (there is a limit to this process...eventually the Hubble camera will become saturated which is similar to overexposing a film picture).

Also, having a larger collecting area allows a smaller details to be seen in the image (or alternately, having two or more telescope placed a distance away from each other and doing interferometry can also increase the resolution).

And of course, Hubble is above the Earth's atmosphere as someone mentioned. It does not have to deal with the distortion which limits even the best ground based telescopes to about 1 arc second resolution on a good night (unless you use adaptive optics). You also don't have to worry about pollution, clouds, and light pollution.

The big problem is that there is only one of them and it's pretty darn expensive to make another! The NGST (Next Generation Space Telescope) has a projected launch date of late this decade and will have a larger mirror and operate in the infrared to see highly red shifted objects.

In the mean time, there is a proposal for a small infrared telescope called PRIME (Primordial Explorer) to be launched in 2005 I think. It would conduct an infrared survey of the sky, similar to the Sloan Digital Sky Survey and would be used for target selection for the NGST.

Rob

Rob

Mr. X
2001-Dec-19, 01:11 AM
Double post, Hale_Bopp

Even when if you look through a telescope and get the impression you're "closer" to the object, you really aren't (Oooh, do I sound stupid saying this or what?). The photons you receive are the "same" you would receive with your eyes. To get to your eyes they travelled a similar distance, only through the telescope.

As some guy said, "stuff" (can be jupiter, the moon, a rare bird or your neighbors /phpBB/images/smiles/icon_smile.gif ) you look at with your telescope only looks larger.

DStahl
2001-Dec-19, 07:37 AM
Insofar as looking back to Planck time, we can only do that indirectly. For one thing, photons of light could not travel freely through space until the primordial plasma deionized and formed stable atoms, so visual information from before that era is preserved only in the CBR. And from that time until the formation of the first galaxies (or the first quasars) there is nothing bright enough to see at the immense distances involved (single stars may have formed as early as half a billion years after the BB, I think, but we could not observe single stars at 10 or 15 billion lightyears' distance). So the upshot is, excepting the cosmic background radiation the farthest we can expect to look back toward the beginning of the Universe is the time of the formation of the first quasars--possibly a billion years or so after the Planck era.

--Don

<font size=-1>[ This Message was edited by: DStahl on 2001-12-19 02:40 ]</font>

GrapesOfWrath
2001-Dec-20, 02:09 PM
On 2001-12-18 12:20, Semirhage wrote:
That is, what precisely is Hubble doing that allows it to see 'back in time' more than I see back in time with my eyes, if it does in fact do so?
Hubble has a better view than we do here under the obscuring blanket of our atmosphere, so it can see fainter objects more clearly. Those fainter objects are often farther away, therefore they are further "back in time."

ljbrs
2001-Dec-24, 12:03 AM
There are a number of interesting ways of measuring the Universe.

For the Solar System there is the use of lasers.

For within our Milky Way (The Galaxy), there are: trigonometric parallax, binary and multiple stars, the motion of nearby stars, etc.

For extragalactic measurements, there are: Cepheid variable stars, type Ia supernovae (particularly useful for accuracy at great distances) and type II supernovae, novae, RR Lyrae variables, etc.

For secondary indicators, there are HII regions and globular clusters, etc.

For great cosmological distances, there is Redshift (using look-back time - FROM the REDSHIFT), always used in combination with other distance measurements.

A greater combination of these methods is used for increased accuracy.

To me, it has always been fascinating that so many methods have been found for measuring the Universe.

I have found that the text, *The Cosmological Distance Ladder* (1985) perhaps out of print, is excellent for explaining these methods in great detail. It is written by one of my favorites, Michael Rowan-Robinson. Hopefully, there may be a newer edition with additional and more recent methods.

ljbrs /phpBB/images/smiles/icon_smile.gif

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*Nothing is more damaging to a new truth than an old error.* Goethe

<font size=-1>[ This Message was edited by: ljbrs on 2001-12-23 19:05 ]</font>