The Sloan Digital Sky Survey

This week I tried to stay on topic and I tried to find just one article and stick to it but that wasn't possible. I looked at the different places the Sloan Digital Sky Survey (SDSS) data is used. I've been very interested in the SDSS because it is the largest sky survey so it's possible to rely entirely on the data from SDSS to model large sections of the sky. However, the services I tried out this week sometimes pull data from other sky surveys to supplement SDSS.

On the SDSS and SDSS Sky Server site there are a few different ways to access images from the survey, there are many photos throughout the sites that can be enlarged including some image galleries and a listing of Famous Places. The way to look at the original data is to locate the original Flexible Image Transport System (FITS) files. There's currently seven data releases on the SDSS site and for every data release it's possible to either select coordinates for viewing or navigate through several levels in a directory to get to a list of FITS files. To view the FITS files download a FITS viewer. Not surprisingly, it's difficult to engage the public with the original data from this survey.

It's probably an understatement to say that astronomers have complicated ways to describe astronomical objects. After creating multiple metadata schemas to organize the massive amount of data from telescopes, astronomers are still having a hard time with descriptions. More accurately, there's images and data about the images, but it still isn't processed and understood by humans. Since there are so many astronomical objects that need to be classified, a team of astronomers, cosmologists and a few other experts created Galaxy Zoo. In order to understand how galaxies are formed and how to describe them, Galaxy Zoo has crowdsourced JPG images from SDSS. There is absolutely nothing technical on the Galaxy Zoo site, they don't mention FITS or metadata, all they are interested in are people's answers to simple questions about JPG images of galaxies.

At first I was skeptical of how successful Galaxy Zoo could be, but after reading what they've discovered I've embraced their practices.

Google Sky is another place where the SDSS images are used, the March 2008 NVO Newsletter provides some details on Google Sky. Google Sky started as an extension to Google Earth and in March 2008 it was also launched at google.com/sky. Google Sky is marked up with Keyhold Markup Language (KML), which means that anybody can participate in tagging. You can also convert a FITS file to KML and upload it or even convert a VOTable to KML with the NVO's Visual Integration and Mining Tools.

I looked around for information on how SDSS was ingested into Google Sky and if there's bad KMZ files in Google Sky, but I wasn't able to find anything.

A service that is similar to Google Sky is sky-map.org. I think this collection is curated even better than Google Sky, the maps of astronomical objects are much more compelling than the ones Google Sky selects and there's more insight to how the SDSS collects data. For instance, in this map the survey "stripes" are visible. There isn't a lot written about sky-map.org aside from what's found in their wiki and a few old articles from magazines.

A fourth place that uses SDSS is the Microsoft WorldWide Telescope (WWT). This software coplies with International Virtual Observatory Alliance standards which means that it uses the Astronomy Visualization Metadata (AVM) standard, so any user can tag in WWT. I haven't used WWT but I read on Wikipedia that it made an astronomer cry.