Comments on: Rendering the Structure of the Universe in Your Spare Time

By: Jeff Bryant

Jeff Bryant — Mon, 18 Apr 2011 16:01:05 +0000

Its been quite a while and I’m not usually a database guy. I didn’t make the database calls from Mathematica since their website didn’t make it obvious how to do that, but I was able to get the data using the following SQL commands:

SELECT
sp.bestObjID as oid,
sp.z as z,
sp.specClass as specClass,
sp.ra as ra,
sp.dec as dec,
sp.mag_0 as mag_g,
sp.mag_1 as mag_r,
sp.mag_2 as mag_i,
gal.expMag_r as emag_r,
gal.expAB_r as AB,
gal.expPhi_r as phi,
gal.expRad_r as rad_r,
gal.expRad_i as rad_i,
gal.petroR90_r / gal.petroR50_r as conc90_50
FROM SpecObj as sp,
Galaxy as gal
WHERE sp.bestObjID = gal.objID
and sp.z = 16000

The last line needs to be tweaked to get a specific batch. Their site times out if the batch is too large. I downloaded each batch to a CSV file and then imported them. Each row had the form:

{”oid”, “z”, “specClass”, “ra”, “dec”, “mag_g”, “mag_r”, “mag_i”, “emag_r”, “AB”, “phi”, “rad_r”, “rad_i”, “conc90_50″}

To transform this data into something ready to be plotted in 3D, I used:

proj = reduceddata /. {z_, ra_,
dec_} :> {z Cos[ra Degree] Sin[dec Degree + Pi/2],
z Sin[ra Degree] Sin[dec Degree + Pi/2], z Cos[dec Degree + Pi/2]}

DIstance was not computed. Only redshift is plotted directly.

By: Mark

Mark — Sun, 17 Apr 2011 22:36:04 +0000

great stuff, but trying to replicate all I got was a sphrical distribution of the points with a bright line in the middle. Could you please post the SQL code you used to obtain the data and also what distance scale did you use and how you converted from z to distance, here is what I used in the SQL:
select ra,dec,z
from specObj WHERE
z BETWEEN 0.001 AND 0.5

Thanks.

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By: jason

jason — Wed, 07 Oct 2009 06:32:32 +0000

this is amazing! thank you!

By: Paul Eipper

Paul Eipper — Wed, 07 Oct 2009 04:36:19 +0000

Really cool. The Mathematica code really is short too, impressive.

I think I’ve seen this rendered somewhere else too, oh yeah, the Millenium Simulation: http://www.mpa-garching.mpg.de/galform/millennium/

Awesome stuff

By: David

David — Wed, 07 Oct 2009 02:53:56 +0000

Good post, but it could have been much better. What were the MMA commands used to query the SDSS databases? What processing was required for the data? Did you try other view points?

Answers to all these might have made a much much better post.

By: Shears

Shears — Tue, 06 Oct 2009 19:51:11 +0000

Unfortunately youtube seems to have some problems because i can’t load the video. From your description it seems a very interesting animation.