Limitations of Observing Distant Space Objects

[jedishrfu]

I think we need to step back a little and explain how we know how far away some astronomical object is.

There are several schemes that have been used that are described in this NASA article:

https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question39.html

1) radar -- for planets and asteroids
2) parallax -- for nearby stars
3) cepheid variable stars -- for distances within our galaxy to star clusters and to nearby galaxies
4) supernovas -- for near by galaxies
5) redshift and the Hubble's law -- for the most distant objects



The methods overlap each other and so its possible to use radar to measure the distance to a planet and then verify that parallax works well. Next we can use parallax to a nearby cepheid variable star to calibrate the cepheid yardstick... We build a set of ladders to farther and farther distances.

You mentioned whether we can see the distant star close up like we see our sun. No we cannot as we don't get enough light to construct a detailed image of the star like we can with the sun. For the most part, stars are treated as point sources of light where we can do spectral analysis to get a composition of elements but no image.

Think about how much dust the light has traveled through and how that in itself would make any image fuzzy.

 

[phyzguy]

The Physicists observing distant flamed objects and trated it as light photons and use speed of light as bassis to estimate time elapsed for light photons traveled from the flamed object.
Again we are looking at flamed object in universe, not a light photons.

I think you are confused by what it means to see something. Everything we see we see because photons from the object travel through space and enter our eyes. When you see "we are looking at flamed object", what you mean is that photons from the flamed object are traveling into our eyes and our eyes are making an image of the flamed object.

 

[vanhees71]

Here's a very clear paper about the correct conceptions of horizons and all that in the FLRW-metric based standard cosmology:

https://arxiv.org/abs/astro-ph/0310808
https://doi.org/10.1071/AS03040

 

[PeterDonis]

Experimental fact, thank you for the correction.
How the finite speed of light used to make the scynteist

...the scientists sure of their claim.

Obviously if light travels at a finite speed, it takes time for light to travel from the object that emits it to you receiving it. The light shows you the object as it was when the light was emitted, which will be a finite time earlier than the time you see it. I don't see what the problem is.

 

[laith salim]

View attachment 334018

You don't have to comment if you don't have a convincing answer or you did not understand the question as a respect for everybody, thanks

Obviously if light travels at a finite speed, it takes time for light to travel from the object that emits it to you receiving it. The light shows you the object as it was when the light was emitted, which will be a finite time earlier than the time you see it. I don't see what the problem is.

When we look at burning tree, we don't say we looking at light, we say we are looking at fire, flames or burning object because that we are observing. Burning object is a burning object and not a light.
Time, speed and distance are related, in order to calculate a true value of any of them, it is required that all of the three to have a true value, in order to have a true measure of time then you have to do the real distance, by using telescopes to observe a star, you are standing still and zooming in an instrument to magnify an distant object, there is no real distance traveled to have a true value of time. What actualy the telescope measuring is the estimate time reqired to travel that distane. there is no solid evidence that light photons will take that long journey through the dark matter and reach your eyes billions earth years later, there is no solid convincing link between observation and time that I'm aware of.

 

[PeterDonis]

there is no solid convincing link between observation and time that I'm aware of.

I'm sorry, but this discussion is going nowhere. You keep repeating the same wrong things and you are not listening to any of our responses.

Thread closed.

 

[Drakkith]

I know the thread is locked, but I wanted to include the following for others that may view it in the future.

Burning object is a burning object and not a light.

1. Yes, it is. Burning objects have been used as light sources for many, many millennia.
2. Even objects that aren't light sources still require that light reflects off of them to be seen, so the speed of light still must be taken into account.

Time, speed and distance are related, in order to calculate a true value of any of them, it is required that all of the three to have a true value, in order to have a true measure of time then you have to do the real distance, by using telescopes to observe a star, you are standing still and zooming in an instrument to magnify an distant object, there is no real distance traveled to have a true value of time. What actualy the telescope measuring is the estimate time reqired to travel that distane.

We don't measure the distance to a star by simply 'looking through a telescope' at it. For close objects we can use parallax measurements. For more distant objects we use other methods. See the following:
https://en.wikipedia.org/wiki/Cosmic_distance_ladder
https://www.uwa.edu.au/science/-/me...Explanation-of-the-cosmic-distance-ladder.pdf

there is no solid evidence that light photons will take that long journey through the dark matter and reach your eyes billions earth years later, there is no solid convincing link between observation and time that I'm aware of.

The finite speed of light is trivial to measure with modern instruments. You can do it on an optical bench in a lab at a university. Combine this with the distance measurements to far away stellar objects and we can get the flight times of light from those objects.

You are simply wrong and you need to accept it.

 

[PeterDonis]

We don't measure the distance to a star by simply 'looking through a telescope' at it.

Just to add: we also don't measure the time it took the light to travel by looking through a telescope; the OP's claim that "What actualy the telescope measuring is the estimate time reqired to travel that distance" is wrong. Telescopes can measure the apparent brightness and angular size of objects. With suitable equipment they can also measure the redshift of the light from those objects. It is the relationships between those three observables that gives us the input we need to calculate things like the distance to the object and the time it took the light to travel. Such calculations of course also make use of models of our universe constructed using General Relativity, and we compare various models by how well their predictions match the actual relationships between observables that we measure.

 

[jedishrfu]

The thread is now officially closed.

Thank you all for participating here.

I would ask the OP to reread what has been written to improve their understanding of the physics of astronomical observation. This is part of an emerging area of astronomy known as multi-messenger astronomy where we observe the full spectrum of light, including radio emissions as well as gravitational waves and neutrino emissions from astronomical events to better understand the processes involved.

https://en.wikipedia.org/wiki/Multi-messenger_astronomy

Jedi