Old Light, Eyes, Telescopes, Light Speed

[bodyload]

I am a firm believer that the further you look into space with a telescope the older the transmissions of light one can see, and therefore shall you be in a distant galaxy and you observe Earth with a very powerful telescope that you may be able to see Earth during, perhaps say, the Jurassic Period.

 

But it wasn't until I began to become involved in optics that I began to have some questions.

I know that light travels ~186,000 miles/second.

I also know that the larger the aperture, the more light is able to be collected.

 

But the speed of light is constant.

 

On the face of things, it began to become apparent to me that the light hitting the telescope lenses is hitting the eye at essentially the same time.

 

It seems to me that no matter the size of the aperture, and whether light is both a particle and a wave, that there would be a succession of years and years of light coming at the telescope that is still bound by the speed of light.

 

So the example which is easiest for me to understand is if a star burns out, our eyes and weak telescopes will see nothing. But if we point a very very powerful telescope to the area of the burned out star, that we can still observe the light that it had emitted in all its glory, perhaps that from billions of years ago, when it was a strong glowing star.

 

But regardless of the lens that you use, light travels at a finite speed.

-------------

 

What allows us to catch the emitted waves or particles of energy faster with an extremely powerful telescope?

 

Is it just the specific lens used or the aperture size? (ie- bigger aperture size=more light allowed in)

 

Is it just bouncing back and forth transmissions from radio telescopes that is orientating to us, Humans, the location of the light and, then forth, the time at which that particular 'light' was emitted?

 

Is it just in adjusting the telescope's focus-point to discover the age of the light?

 

What is it about Telescopic lenses that allow us to see faster than the human eye?

Edited September 9, 2016 by bodyload

[Sensei]

So the example which is easiest for me to understand is if a star burns out, our eyes and weak telescopes will see nothing. But if we point a very very powerful telescope to the area of the burned out star, that we can still observe the light that it had emitted in all its glory, perhaps that from billions of years ago, when it was a strong glowing star.

Ideal point light source, is emitting photons in the all directions, and obeying inverse-square law:

[math]P=\frac{P_0}{4\pi r^2}[/math]

 

P₀ is initial power of star, in Watts = Joules per second.

P is power per area unit here on the Earth, in Watts per meter square = Joules per meter square per second.

 

https://en.wikipedia.org/wiki/Inverse-square_law

 

So, the larger area of device, the more photons can be reflected/refracted by lens, and then absorbed.

Star that burned entirely from our point of view is invisible. It can still be seen burning, from other galaxy "behind us", because "final" photons didn't arrive there yet.

But they will see much smaller quantity of photons per their area unit.

 

Star that is invisible, it's invisible in 400nm- 700nm visible photon spectrum range, it can still be seen in f.e. infra-red or radiowave spectrum range.

It depends on temperature. Hot body sends higher energy photons. See black body radiation article.

https://en.wikipedia.org/wiki/Black-body_radiation

 

You can't see that tea/coffee is hot or cold. It's temperature is ~90-100 C (373.15 K).

But if you would use infra-red camera, you would instantly see it as red-yellow-white colored on the display, significantly hotter than surrounding environment (f.e. 25 C).

The hotter body, the more energetic photons emitted.

Edited September 9, 2016 by Sensei

[swansont]

 

What allows use to catch the emitted waves or particles of energy faster with an extremely powerful telescope?

 

 

You don't catch the photons faster. You catch more of them.

[bodyload]

 

OK.

So in most cases the whole idea of 'seeing' the 'history' of the universe through 'old light' does not apply to how optics work on the superficial of a man setting up a telescope in the park?

 

And also you are saying that the light that has reached us is so dispersed that shall we have a powerful telescope (yet of the 'run-of-the-mill' type of eye-telescope optics) that we can see a more 'compact', older signal of light (shall we look further)?

 

--------

 

My other question is when you have a constant 'stream' of light coming at you, is there some sort of focusing mechanism on these extremely complex telescopes that allows you to capture an 'mri-like' slice of that million year old image-in-time?

 

 

 

 

 

You don't catch the photons faster. You catch more of them.

 

What allows one to distinguish the relative time the photons (or waves) were emitted?

Because aren't you catching all the photons (or waves) at any one measured-time?

Edited September 9, 2016 by bodyload

[swansont]

 

What allows one to distinguish the relative time the photons (or waves) were emitted?

Because aren't you catching all the photons (or waves) at any one measured-time?

 

 

It depends on how far away the source is. You catch the photons from that direction, but if your field of view is narrow enough, you don't have multiple sources.

[Sensei]

You look at star, focus optics on it, and measure its properties like intensity.

Repeat it over and over again at various days of year (especially +90, +180, +270 days later)

This way astronomer can calculate parallax.

https://en.wikipedia.org/wiki/Stellar_parallax

and calculate distance to a star in close area.

Once you have distance, once you know intensity, various other things about star can be calculated.

Reverse inverse-square law, and you have initial power of star, and its temperature. Composition can be estimated by analyze of spectral lines.

If it's wobbling, it could mean there is 2nd star, or planet(s).

If it's periodically blinking (decrease of intensity), it could mean there is planet (or couple of them) obscuring surface of star.

etc. etc.

 

While watching area where there is nothing in weaker telescope, after even minutes, days or months of watching that area, the more and more photons from that region arrives,

and after computer analyze new object can be identified.

 

You can't look at star, and expecting you will see what is behind that star (except situation as in gravitational lensing).

But at various days of year, star is obscuring slightly different region of sky behind it.

 

What allows one to distinguish the relative time the photons (or waves) were emitted?

d=c*t

so

t=d/c

 

where

d is distance to object in meters,

t is time spend on flying in seconds,

c is speed of light 299792458 m/s

 

Distance d is calculated using parallax or other method.

Edited September 9, 2016 by Sensei

[bodyload]

So using 'regular' optics that don't measure outside the field of human's visual wavelength field (or using 'regular' optics of/within the range of human-eye visual wavelengths), how far into the past can we see using our best optics (in and out of Earth's atmosphere)?

Edited September 9, 2016 by bodyload

[Strange]

So using 'regular' optics that don't measure outside the field of human's visual wavelength field (or using 'regular' optics of/within the range of human-eye visual wavelengths), how far into the past can we see using our best optics (in and out of Earth's atmosphere)?

 

 

The wavelength measured are important because of increasing red-shift with distance. So, for example, the oldest light we can see is the cosmic microwave background. But, as the name suggests, that is microwaves and so requires specialised detectors. That dates from about 360,000 years after the (notional) "start" of the universe.

 

If you want to know what is the oldest visible light, then that is a much more complicated question. But the oldest galaxies that we can see are about 13.39 billions years old.

https://en.wikipedia.org/wiki/GN-z11