Friday, August 14, 2009

More Better Redshift

I just received a response from NASA on the questions I raised in this post about redshift data that seemed incorrect. NASA responded that they have fixed the errors in the redshift data provided on their web pages. The new corrected data is shown in the chart above and looks much nicer.

The only flaws left are two different redshift values given for a distance of 12 BLY and redshift data for ACO 3341 which seems out of sync. The two different values for 12 BLY can be written off as a rounding error that occurs when the distance is simplified for the use in the press release. The ACO 3341 data was not provided by NASA. It was provided by the European Organization for Astronomical Research in the Southern Hemisphere (ESO). Just to wrap things up, I'll send them an e-mail and see if I can get an explanation or correction to their data, but things are looking pretty good now. LATE EDIT: Olivier Hainaut of the ESO has responded the redshift z and distance data released on the web page contained a typo and has been corrected. The page now gives the distance as "almost 500MLy". My thanks to him for taking the time to do this.

I'd like to thank the folks at the Chandra X-ray Observatory, Dr. Tom Bridgman, and reader jeant8 who is so smart she must work for NASA and if not, should, for working to clear up all this.

In the course of all this, some links to some pretty interesting Astronomy websites were provided. I'll reproduce those, along with sources for the new data, below.

Useful Links

The Sloan Digital Sky Survey and and
The SDSS has a publicly accessible database of images and data for 25% of the sky. Proper use of this database requires a bit of skill but there are tutorials provided.

The ESA/ESO/NASA Photoshop FITS Liberator
A Photoshop plugin for working with data in the FITS format. FITS data is what is produced by the SDSS public database.

NASA/IPAC Extragalactic Database
Data on extragalactic objects. Easier to use that SDSS.

Ned Wright's Cosmology Calculator and
A Javascript calculator for determining distance values based on different values for redshift z, the Hubble Constant, and the Omega M and Omega Vacuum constants. The second link provides an introduction to cosmology.

A collection of tables and such taken from published astronomy papers.

John Huchra's website explaining the Hubble constant

Communicating Astronomy with the Public
A journal devoted to communicating astronomy facts to the public.

Distance of Virgo, Coma and other clusters and and and and and
Papers discussing this issue.

Redshift z values are multiplied by 10,000 in the charts I provided. This was done so they'd be on a similar scale to distance values, otherwise you wouldn't be able to see them in the charts that had scales large enough to show distances. Scaling the redshift z values in this way does not affect the results I discuss here.




  1. Disclaimer: I am not "of NASA". I'm a contractor and cannot/do not speak for the organization.

    You should consider plotting your data as a scatter plot. This will give better agreement for z>1. See
    I believe you are plotting Dltt in the bottom graph on this page.

  2. My apologies Dr. Bridgman. I'll correct the error.

    Thanks again for your help in this.