All Questions
30
questions
7
votes
3
answers
2k
views
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 ...
- 171
2
votes
1
answer
134
views
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 ...
- 171
1
vote
1
answer
113
views
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
votes
1
answer
2k
views
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
votes
1
answer
108
views
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
votes
1
answer
277
views
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
votes
1
answer
333
views
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
vote
1
answer
208
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
111
views
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?
- 2,620
2
votes
0
answers
60
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
views
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
votes
1
answer
1k
views
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 ...
- 5,307
0
votes
0
answers
58
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-...
- 6,684
1
vote
1
answer
4k
views
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
106
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 ...
- 3,137