by VictorBorun » Fri Jun 09, 2023 11:02 pm
Chris Peterson wrote: ↑Fri Jun 09, 2023 9:29 pm
Roeland wrote: ↑Fri Jun 09, 2023 8:44 pm
""At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years."
This can't be correct. Maybe 60 million?
6 million sounds reasonable. At a distance of 4 billion ly and a span of 6 million ly, that corresponds to a subtended angle of 5 arcmin. The NIRCam FOV is 2.2 arcmin for each of its pair of sensors.
We need to detail a convention.
My favourite is to label the picture of a distant galaxy or cluster a few billion ly away with metrics of the moment in time when the light was emitted. The angle size of that galaxy or cluster for an observer in the point where Milky Way is growing and Solar system might already exist was the same all the billions of years the photons were travelling, but the distance grew by (1+redshift) times.
So an angle size of 5 arcmin = 0.00145444 radians translates to 6 million ly at 4.14 billion ly distance at the moment the photons were emitted.
I am comfortable with the use of this measure of distance, but they usually publish other things.
4.14 billion ly of
angular size distance converts to
redshift = 0.498
age (since the Big Bang) 8.642 billion years + light travel time 5.078 billion years = 13.72 our present age (since the Big Bang)
comoving radial distance, which is most popular, is 6.204 billion ly
[quote="Chris Peterson" post_id=331610 time=1686346147 user_id=117706]
[quote=Roeland post_id=331608 time=1686343441]
""At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years."
This can't be correct. Maybe 60 million?
[/quote]
6 million sounds reasonable. At a distance of 4 billion ly and a span of 6 million ly, that corresponds to a subtended angle of 5 arcmin. The NIRCam FOV is 2.2 arcmin for each of its pair of sensors.
[/quote]
We need to detail a convention.
My favourite is to label the picture of a distant galaxy or cluster a few billion ly away with metrics of the moment in time when the light was emitted. The angle size of that galaxy or cluster for an observer in the point where Milky Way is growing and Solar system might already exist was the same all the billions of years the photons were travelling, but the distance grew by (1+redshift) times.
So an angle size of 5 arcmin = 0.00145444 radians translates to 6 million ly at 4.14 billion ly distance at the moment the photons were emitted.
I am comfortable with the use of this measure of distance, but they usually publish other things.
4.14 billion ly of [i]angular size distance[/i] [url=https://www.astro.ucla.edu/~wright/CosmoCalc.html]converts[/url] to
redshift = 0.498
age (since the Big Bang) 8.642 billion years + light travel time 5.078 billion years = 13.72 our present age (since the Big Bang)
[i]comoving radial distance[/i], which is most popular, is 6.204 billion ly