All Questions
32 questions
1
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83
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Cosmological redshift to distance calculation: Why are imaginary numbers involved?
I was looking at this question and read through the linked article http://arxiv.org/pdf/astro-ph/0007341v1.pdf. When I was attempting to compute the distance between two galaxies using the following ...
- 6,733
-9
votes
1
answer
608
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What are we misunderstanding about the scale factor-redshift relation? [closed]
If the scale factor as a function of time represents or is equal to the average distance between the galaxies, then it increases altogether with the CMB redshift $z$, but it also must be equal to the ...
user57748
7
votes
3
answers
2k
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How do we work out the light travel time on a cosmic scale?
I just read this article in the AUSTRALIAN SKY & TELESCOPE magazine, Nov/Dec 2022 Issue 140, on P16, KEEP YOUR DISTANCE: How far away are the objects we see in the universe? And on P23:
"And ...
user54537
2
votes
1
answer
175
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Why are distant type Ia supernovae dimmer than expected?
Why are the (extremely) distant type Ia supernovae dimmer than expected?
Relative to what? Their cosmological red shift? Well, what else.
Please don't just say "Because the expansion is ...
user54537
1
vote
1
answer
148
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Finding an expression for the rate of change of Comoving volume with respect to redshift
I am trying to find the expression for the rate of change of comoving volume with respect to redshift, that is $\frac{\mathrm{d}V_c}{\mathrm{d}z}$. In this paper (Hogg, David W.), the comoving volume ...
- 75
8
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1
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2k
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Is Webb or any near-future telescopes like ELT capable of observing redshift changes to confirm General Relativity?
The (Davis and Lineweaver (2003)) "Expanding Confusion" paper states that "the expected change in redshift due to cosmological acceleration or deceleration is only ∆z ∼ 10^(−8) over 100 ...
- 175
3
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1
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114
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How can we estimate distance of galaxies by only redshift when there are other several factors other than distance to cause redshift
There are different factors for red appearance of different objects in the night sky. Two reasons which I know are
Star red by nature
Example: red supergiants
They emit red light because of their ...
- 121
2
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1
answer
320
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3d distance between the Galaxies inside the galaxy cluster
I am currently working on the dynamics of the galaxy cluster, so i am trying to get the distance between the galaxies inside the galaxy cluster from its centre. As a input i have RA , DEC and Z (...
- 41
3
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1
answer
363
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Redshift distance proportionality at high Z and need for "mighty mouse" galaxies?
Allegedly supported by some evidence from the new James Webb space telescope physicist Eric Lerner has written an article that have garnered some attention. He writes that:
"Put another way, the ...
- 457
1
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1
answer
218
views
Is luminosity distance related to both heliocentric redshift and CMB restframe redshift？
The luminosity distance
$$d_l=(1+z)r(z)\ ,$$
where $r(z)$ is given by $$r(z)=cH^{-1}_0\int_{0}^{z}\frac{dz'}{E(z')}\ .$$
When I use the SNe dataset "Pantheon", I find there are two redshifts:...
- 21
2
votes
1
answer
115
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Photometry templates -- what are the templates of?
Redshift measurements from photometric data can be determined using template-fitting (Cosmos website, SDSS photo-z).
What does it mean to fit a template to determine redshift? What is the template of?
- 2,630
2
votes
0
answers
63
views
How to find the scale factor on given time in the future if initial distance between source and destination is known
Assume the received redshift $z$ of a photon is known. We then can calculate the initial distance (when the received photon was emitted), the light Travel Distance, the current Distance (proper ...
3
votes
1
answer
3k
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Comoving Volume Calculation
Suppose I have data from an astronomical survey at redshifts in the range $z = [2,3]$. Suppose that, on average in this range, the data covers an area on the sky of $A=1$ $\mathrm{Mpc}^2$. How would I ...
- 205
0
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1
answer
1k
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How do you calculate comoving distance and light's travel distance? According to the formulae below?
According to Wikipedia, Distance measures (cosmology),
Comoving distance:
$${\displaystyle d_{C}(z)=d_{H}\int _{0}^{z}{\frac {dz'}{E(z')}}}$$
Light-travel distance:
$${\displaystyle d_{T}(z)=d_{H}\int ...
- 5,585
0
votes
0
answers
59
views
How long does it take for a galaxy (or other object) to disappear behind the cosmic sight horizon?
After looking at this question, I am wondering, how long does it take for a galaxy or other space object, to disappear from our view from the Milky Way due to the expansion of the universe? Assume GN-...
- 6,733
1
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1
answer
5k
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How to find the distance between two galaxies from ra and dec and redshift [duplicate]
I have ra and dec and corresponding redshift of galaxies. I would like to calculate the distance between two galaxies.
I did like this to find the nearest neighbour galaxies.
Suppose I am trying to ...
- 11
3
votes
1
answer
107
views
Were radio spectroscopic observations ever used to first measure a distance successfully?
Usually, especially for an extragalactic object, its redshift is determined by optical spectroscopic redshift. But the angular resolution of early radio observations is poor and an optical counterpart ...
- 3,157
1
vote
1
answer
671
views
How do we determine a redshift error?
I am struggling to calculate the redshift error of a galaxy. I was able to determine the redshifts of the absorption and emission lines from the galaxy's spectrum and then took the average of the ...
- 165
2
votes
0
answers
66
views
Minimum apparent magnitude of galaxy
currently I'm working on astronomy problem which deals with finding redshift of a galaxy. But the first part asks to derermine apparent magnitude of a galaxy:
Find what should be the minimum ...
- 23
1
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0
answers
61
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How the depth[Mpc] is obtained from the redshift
I read this paper. In this paper, they show the three-dimensional distribution of the [OII] emitters.
It is mentioned that The depth in z-axis is converted from the redshift, which is estimated from ...
- 61
2
votes
1
answer
1k
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Redshift, velocity, distance
How are redshift, (recessional) velocity and distance of a galaxy related?
I understand what v=HD states. So I assume that Hubble measured a direct relation between the distance and recessional ...
- 165
4
votes
3
answers
890
views
How do we measure distance in space?
I know that you can calculate the distance to another star for example, by using the phenomenon redshift to determine how much it has redshifted because of the expansion of the universe. But how do ...
- 187
13
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1
answer
2k
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How do we know if an object is redshifted?
I have some questions about redshift. I think that the first two hang on the last two, but feel free to point out anything you think I should know.
How do we know if an object is actually redshifted,...
- 179
5
votes
2
answers
1k
views
Comoving distance between two points [(RA1, Dec1, z1) and (RA2, Dec2, z2)]
I have Redshift (z), RA and Dec positions for two points in a galaxy catalogue (say P1 = [<...
- 151
2
votes
2
answers
217
views
How far away is this galaxy?
Arp 299 is in the news, with most sources reporting it as 140 or 150 million light-years away. But what kind of distance is this?
The paper which is trhe source for the news item has Supplementary ...
- 383
3
votes
1
answer
2k
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Question from Introduction to Modern Cosmology by Andrew Liddle
The exact question goes like this:
In the real Universe the expansion is not completely uniform. Rather, galaxies exhibit
some random motion relative to the overall Hubble expansion, known as their
...
- 61
1
vote
0
answers
115
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How can you estimate distance of an object by its redshift? [duplicate]
Is there a way to take the red shift of an object and, from that, calculate a rough estimate of its distance from us (in parsecs, preferably)?
- 843
18
votes
2
answers
9k
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Understanding The Turnover Point of Angular Diameter Distance
I am trying to get a better understanding of cosmological distances, in particular the angular diameter distance which I have also seen referred to as angular size distance.
What I am looking for is ...
- 183
4
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4
answers
16k
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How do you calculate the lookback time distance to a given galaxy?
By lookback time distance I mean the same as light-travel distance.
Can it be calculated from just knowing the redshift?
- 559
8
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2
answers
5k
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Do objects look larger the further away they are, beyond z=1?
I stumbled upon this text which illustrates and says:
We find that as the object is moved to higher redshifts its angular
size first decreases (as naively expected) but soon begins to increase
...
- 11.5k
3
votes
3
answers
774
views
Conundrum involving distance to object, universal expansion, age of universe, etc
I was recently reading about a galaxy or quasar (not sure which, so lets just say quasar) where the estimated distance to this thing was some very significant fraction of the age of the universe. ...
- 381
23
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1
answer
2k
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How distances are measured in the Solar System, in the Galaxy, and in the Universe?
Distances in our universe can be calculated in several ways:
Stellar Parallax
Standard Candles
Redshift
How are these methods linked, and how they are actually used to calculate distances are ...
