APOD: A Redshift Lookup Table for our Universe (2013 Apr 08)

[stephen63]

Never mind. The objects ARE receding faster, as indicated by the red shift.

I don't think they are receding faster than my hair line

Who knew? A relativistic bald spot!

[K1NS]

It's a nomograph . . .

Yes, that's the word. It's not just a "table," it's a nomograph!

[Chris Peterson]

It's a nomograph . . .

Yes, that's the word. It's not just a "table," it's a nomograph! :D

Per a previous discussion here, "nomograph" isn't quite the right word. As Art suggested, "slide" is better, since the values are always read off horizontally (a nomograph typically involves a calculation of two variables, made by drawing a line between those values in a pair of columns, and reading the answer where that line intersects a third column).

[neufer]

[b][color=#0000FF]Polar stereographic projection of Earth with the equator at a radius z=1 (vs. z= ∞ for the South Pole). (Distant objects may appear larger/closer than they actually are.)[/color][/b]

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... what's up with the 1" scale and the kpc scales? Seems like (for the 1") 8.7 is the magic number, around which there's a kind of strange symmetry. I would have thought that there's a linear distance-size relationship. Obviously, there's something more complicated to this than meets the eye.

Think of yourself at the north pole with a cold clear global atmospheric inversion near the surface such that you can literally see as far as you like. By looking down the Oº meridian (i.e., line of longitude) and the 1º meridian you view distant objects that are physically further & further apart until (as you view objects as far away as the equator) they are 60 nautical miles apart. After that, more distant objects in the Southern Hemisphere are physically closer & closer together until you simply observe the tiny South pole down both meridians.

Hence, in this situation, 60 nautical miles is "the magic number around which there's a kind of strange symmetry." This symmetry happens at precisely the half way point (i.e., 9Oº latitude distance) or in polar stereographic projection terms at precisely a radius z=1 (vs. z= ∞ for the South Pole).

The fact that the Redshift Lookup Table doesn't also show strange symmetry at precisely "the half way point" (i.e., 13.8/2 = 6.9 Gyr distance) or at precisely z=1 (vs. z= ∞ for the tiny Big Bang) is due to the complication of Dark Energy Expansion. (This expansion situation is probably analogous to a pear shaped Earth.)

[Ann]

This post is only tangentially linked to today's Apod, but it is this chart by Pilipenko that sparked off my interest when it was first posted in Breaking Science News some days ago.

I'm intrigued to know the redshift of CMB and what the emitting wavelength was.

The quotations below (and other sources I've looked at) give the estimated temperature of the original radiation but not the wavelength.

That is your answer. The CMB is not seen as one wavelength today, because it was not emitted as a single wavelength. The CMB is observed as a blackbody spectrum, which peaks at about 2 mm. That is the blackbody spectrum equivalent for a radiator at 2.7 K. When the photons were emitted, the source temperature was about 3000 K, meaning the spectrum peaked at a bit under 1 micrometer, just into the near IR. Visually, the light would have appeared warm white.

You mean we're talking about a universe-sized Betelgeuse? How big was that universe?

Ann

[MargaritaMc]

This post is only tangentially linked to today's Apod, but it is this chart by Pilipenko that sparked off my interest when it was first posted in Breaking Science News some days ago.

I'm intrigued to know the redshift of CMB and what the emitting wavelength was.

The quotations below (and other sources I've looked at) give the estimated temperature of the original radiation but not the wavelength.

That is your answer. The CMB is not seen as one wavelength today, because it was not emitted as a single wavelength. The CMB is observed as a blackbody spectrum, which peaks at about 2 mm. That is the blackbody spectrum equivalent for a radiator at 2.7 K. When the photons were emitted, the source temperature was about 3000 K, meaning the spectrum peaked at a bit under 1 micrometer, just into the near IR. Visually, the light would have appeared warm white.

You mean we're talking about a universe-sized Betelgeuse? How big was that universe?

Ann

Our Universe Part 11: Decoupling Epoch
The universe is now about 379,000 years old. It has expanded to about a thousandth of its present size and it has cooled to about 4000 K.

http://sciexplorer.blogspot.com.es/2011 ... epoch.html


But as we don't know the "present size" of the universe that doesn't take us any further 'forrader'

Margarita

[Ann]

Yes, "unknown size" divided by a thousand doesn't make much sense... but thanks a lot for your answer, Margarita! It does say how much bigger the unvierse has grown since that time, certainly!

By the way, what is "forrader"? (It looks a bit like "förrädare", which is "traitor" in Swedish, but I guess not...)

Ann

[MargaritaMc]

By the way, what is "forrader"? (It looks a bit like "förrädare", which is "traitor" in Swedish, but I guess not...)

Ann

Sorry, Ann - it's early in the morning and I didn't think! (My brain needs much coffee to get it moving...)
'Forrader' is rather old-fashioned English slang meaning 'forward' ('forwarder'). So, "we are no further forrader" just means that we've made no advance.

It isn't a useful bit of linguistic knowledge as I may be one of the few people left on the planet who automatically use the term...

Now - COFFEE!
Margarita

[Chris Peterson]

Yes, "unknown size" divided by a thousand doesn't make much sense...

But I think we can quite safely say that when the photons were released, the Universe was a good deal larger than Betelgeuse!

[eltodesukane]

Sorry to bother about what may have a trivial answer,

But what's up with the 1" scale and the kpc scales? Seems like (for the 1") 8.7 is the magic number, around which there's a kind of strange symmetry. I would have thought that there's a linear distance-size relationship. Obviously, there's something more complicated to this than meets the eye.

In the past the universe was smaller, but it still must fit onto the celestial sphere, so it`s angular size increases as we go back in time. The big bang itself has size zero, but it`s angular size is the whole sky.

[K1NS]

Per a previous discussion here, "nomograph" isn't quite the right word. As Art suggested, "slide" is better, since the values are always read off horizontally (a nomograph typically involves a calculation of two variables, made by drawing a line between those values in a pair of columns, and reading the answer where that line intersects a third column).

Actually, nomographs (or nomograms) can involve several variables. and the lines may or may not be straight. According to the Oxford English Dictionary, nomograms have been around since about 1909. The name comes from the Greek word "nomo" which simply means law, so nomograms are meant to facilitate calculations according to some mathematical or physical law, such as redshift in the universe.

I guess the name "slide" was suggested because this nomograph has a cursory (no pun intended) resemblance to a slide rule. And as a matter of fact, some nomographs are physical devices with cursors and reticules.

I am not aware of the previous discussion, so maybe my comments have already been covered. But I still believe this "table" or "slide" is best called a nomograph.

[neufer]

Yes, "unknown size" divided by a thousand doesn't make much sense...

But I think we can quite safely say that when the photons were released, the Universe was a good deal larger than Betelgeuse!

Your Cosmology Calculator (set to: H₀ = 67.8, Omega_M = 0.268, Omega_vac = 0.692, z = 1089)

gives a scale of 0.069 kpc/" => equivalent to a circumference of ~ 89 Mpc

or slightly smaller than the Virgo Supercluster (circumference of ~ 104 Mpc).