Redshift

[hobbit]

Sometimes I see the distance to an object given as a redshift value. How does this correspond to the distance in lightyears? ie redshift of 1=100 lightyears.

[ausastronomer]

Hi,

Can you provide a link or a reference to where you are referring to seeing this? And maybe the object in question. I am assuming you are referring to the objects redshift z value?

It isn't just a simple conversion factor and primary school maths to work this out.

Cheers
John B

[Astro_Bot]

These might help:

Red Shift (http://hyperphysics.phy-astr.gsu.edu/hbase/astro/redshf.html)

Redshifts (http://skyserver.sdss.org/dr1/en/proj/basic/universe/redshifts.asp)

[hobbit]

Wall: Hercules-Corona Borealis Great Wall
Mean distance:z≈2

[pdalek]

Try WolframAlpha

e.g. z=1.0
http://www.wolframalpha.com/input/?i=redshift+z%3D1.0&a=FSelect_**RedshiftWavelengthFormu la--

[wasyoungonce]

D = zc/H0
where
D = distance
Z = redshift cosmological value
c = speed of light
Ho = Hubble constant 71 Km s expansion per Mpc (per mega parsec).
You need to dimensional analysis to ensure values are the same like c = Kms

Because distance values get so large in metres, km parsecs or mega parsecs or lightyears, then redshift is often referred to as the distance z. The greater the cosmological redshift the greater the distance that object is.

Do not confuse cosmological redshift to wavelength redshift of local galaxies/objects. They have local motion/movement (as well as cosmological redshift movement expansion) that is perciliur to their cluster so their cosmological redshift is more difficult to determine. At high velocities the value of z becomes relativistic opening a whole world of hurt in obtaining their distances.

[hobbit]

Thanks Brendan. That does help and only slightly melted my brain.

[wasyoungonce]

Duke uni runs an online "into to astronomy course (https://www.coursera.org/course/introastro)". I am just completing, quite a few other IIS members have done. Very nice course, explains it all well worth the effort to do, iis thread here. (http://www.iceinspace.com.au/forum/showthread.php?t=114512)