Go Back   IceInSpace > Beginners Start Here > Beginners Talk
Register FAQ Calendar Today's Posts Search

Reply
 
Thread Tools Rate Thread
  #1  
Old 11-02-2014, 12:07 PM
hobbit
Registered User

hobbit is offline
 
Join Date: Oct 2013
Location: Campbelltown
Posts: 379
Redshift

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.
Reply With Quote
  #2  
Old 11-02-2014, 12:43 PM
ausastronomer (John Bambury)
Registered User

ausastronomer is offline
 
Join Date: Mar 2005
Location: Shoalhaven Heads, NSW
Posts: 2,620
Quote:
Originally Posted by hobbit View Post
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.
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
Reply With Quote
  #3  
Old 11-02-2014, 12:50 PM
Astro_Bot's Avatar
Astro_Bot
Registered User

Astro_Bot is offline
 
Join Date: Jun 2012
Location: Brisbane
Posts: 1,605
These might help:

Red Shift

Redshifts
Reply With Quote
  #4  
Old 11-02-2014, 01:24 PM
hobbit
Registered User

hobbit is offline
 
Join Date: Oct 2013
Location: Campbelltown
Posts: 379
Quote:
Originally Posted by ausastronomer View Post
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
Wall: Hercules-Corona Borealis Great Wall
Mean distance:z≈2
Reply With Quote
  #5  
Old 11-02-2014, 03:11 PM
pdalek's Avatar
pdalek (Patrick)
Registered User

pdalek is offline
 
Join Date: Mar 2013
Location: Melbourne, Australia
Posts: 112
Try WolframAlpha

e.g. z=1.0
http://www.wolframalpha.com/input/?i...engthFormula--
Reply With Quote
  #6  
Old 18-02-2014, 10:02 PM
wasyoungonce's Avatar
wasyoungonce (Brendan)
Certified Village Idiot

wasyoungonce is offline
 
Join Date: Jul 2006
Location: Mexico city (Melb), Australia
Posts: 2,359
Quote:
Originally Posted by hobbit View Post
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.
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.
Reply With Quote
  #7  
Old 19-02-2014, 09:33 AM
hobbit
Registered User

hobbit is offline
 
Join Date: Oct 2013
Location: Campbelltown
Posts: 379
Thanks Brendan. That does help and only slightly melted my brain.
Reply With Quote
  #8  
Old 19-02-2014, 09:50 AM
wasyoungonce's Avatar
wasyoungonce (Brendan)
Certified Village Idiot

wasyoungonce is offline
 
Join Date: Jul 2006
Location: Mexico city (Melb), Australia
Posts: 2,359
Duke uni runs an online "into to astronomy course". 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.
Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 05:55 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement