The Hubble Data Archive

As the self appointed curator of Bad Astronomy, I see a lot of misconceptions float my way. As you'd expect, the most popular items in astronomy are the ones with the highest number of misguided ideas. Movies for example: how many tens of millions of people saw the movie Armageddon in 1998, for example? That had more bad astronomy in it than any Bugs Bunny cartoon. News, commercials, you name-- every subject in astronomy has its share of misconceptions.

I think, though, that the Hubble Space Telescope shoulders more than its load. Maybe it's because I work so closely with Hubble data and scientists that the errors I see about it in the public's eye loom so large. Hubble, for example, orbits the Earth, but I have heard more than one person think it's a probe, like Cassini or Galileo, heading off to the stars. Certainly arguments abound about why, sometimes, Hubble data is withheld from public consumption for a year.

Actually that's part of why I am writing about this topic today: what happens to Hubble observations after the telescope points at some object? Not ``what does the scientist do with it?'' but what actually happens to the data themselves? (Note: the word ``data'' is actually plural, and I try to use it that way. The singular is ``datum''. Latin lesson for the day. ;-)

The short answer is: they get archived. At the Space Telescope Science Institute (STScI for short, or, for those in the know, simply ``the 'tute'') there is a vast array of storage for electronic data. It goes more or less like this: Hubble observes an object. The data get sent via radio to computers at Goddard Space Flight Center, which in turn sends them up to Baltimore, where STScI is. The data when they arrive are in no condition for science: they are in a format easy for the telescope to send, but not really meant for scientists to analyze. More computers at the 'tute crunch through the data, converting the telemetry data into something more palatable for the scientists and engineers. After that, the data are sent through a series of standardized software routines, called ``the pipeline'', which further processes the data. The pipeline (which is actually several different pipelines, depending on what part of Hubble you use) calibrates the data: for example, it removes artifacts put into the data by the camera used, and might also remove radiation hits that look like little stars in the data.

After all that, the data are ready to be sent to the astronomer. They can be recorded on tape, sent electronically over the 'net or even picked up by the astronomer, who can visit the 'tute and work on the data there. The data are stored at the 'tute (and also at the Hubble European Coordinating Facility in Garching, Germany) in what is called simply ``The Archive''. After a year, and sometimes less, the data become public. Any astronomer who shows a need can ask for the data.

The archive used to be a fairly closed system; you could access it only through special software and see what's there. However, times have changed a bit. Now you, the public, can actually peek at Hubble data when it becomes non-proprietary. The Archive has a web site with extensive lists of data. The website curator, Tim Kimball, has organized the site so that you can, for example:

• look at interesting data-- this is a list of the prettier datasets, including images of solar system objects (I like Venus), cool nebulae, galaxies and the like.

• see recent data-- data that has been in the archive for a year and is now available to the astronomical community at large.

• randomly look at Hubble's collection of targets-- this page selects 50 random datasets for you to peruse. They are not all very interesting from an aesthetic point of view, but sometimes you find one that is really nice.

When you pick an object, you can download a GIF image of it. Not all the observations are images; some are spectra! You might want to stick with WFPC (Wide Field Planetary Camera), FOC (Faint Object Camera) and STIS (Space Telescope Imaging Spectrograph) data, since those are usually images. Have fun!

By the way, if you really have some time, try browsing the archive's main webpage. From there you'll find lots of things to look at, though as lot of it is aimed at professional astronomers. Stick with the Daily Update page for more palatable entries.