Skywalker: Seeing the sky through a telescope's eye

Size does matter:
In the recent past large high resolution space based imaging surveys for galaxies have been conducted with the Hubble Space Telescope and its Advanced Camera for Surveys (ACS). Examples are the "HST Hubble Ultra Deep Field" (UDF, Beckwith et al. 2006), the observations in the GOODS field (Giavalisco et al. 2004), our own GEMS survey ("Galaxy Evolution from Morphologies and SEDs", Rix et al. 2004), or the ACS-COSMOS project (Scoville et al. 2006), ordered by increasing sky coverage.

These surveys have in common that they produce large contiguous high-resolution images, ranging in size from 3'x3' (UDF) to 1.4°x1.4° (COSMOS). These images are either difficult or impossible to be printed on paper or to be viewed as single images on a screen. As an example the COSMOS mosaic will sport more than 100.000 pixels on a side with corresponding file sizes, even in JPEG format.

This prompted us to write a conceptually rather simple web-based application called the Skywalker (name not endorsed by Lucasfilm), that allows to view the full resolution image mosaic while only loading small pieces of the image at a time. All of this with HTML and JavaScript only, so it can be used from any computer connected to the internet with many different web-browsers and without the installation of any special software.

To present an image via a Skywalker additional work has to be put in, as the image has to be chopped up into many subframes, an overview image has to be created and some JavaScript parameters adapted.

We have recently published a PASP paper on the techniques behind the COSMOS Skywalker, and created a SourceForge.net project to access the COSMOS SkyWalker and pointers to helper tools.

Existing Skywalker projects:
Here is a list of existing Skywalker projects. Offline versions can be downloaded for some of them as well, in that case no internet connection is needed at runtime (unpack into a directory and load index.html into your browser):

They should work with most Mozilla, Firefox, Internet Explorer and Opera Versions. For the realisation of the Skywalkers, we would like to thank the developers of the DynAPI JavaScript library (Steinman et al., 2004) that made programming easy.

Skywalker publications:

  • Jahnke K., Sánchez S. F., Koekemoer A. 2006, PASP, 118, 1186, "Seeing the sky through Hubble's eye: The COSMOS SkyWalker" (ADS | astro-ph)
  • Jahnke K., Sánchez S. F., Häußler B. 2004, "Skywalking GEMS and UDF" (astro-ph)
AIP kj | 13.12.2007.