Using World Coordinates

This recipe demonstrates the simple use of World Coordinates in GAIA. Recall that a World Coordinate System (WCS; see Section ) relates the positions of pixels in an image to celestial coordinate systems on the sky. In practice it allows you to display and annotate images in terms of celestial coordinates.

Some images include a WCS as part of the auxiliary information that they contain; others do not. For example, ngc1275jkt.sdf, the JKT image used in the recipe in Section  does not possess a WCS, but images retrieved from the DSS (as in the recipe in Section ) do. It is possible to use GAIA to add a WCS to an image, and the recipe in Section  is an example doing so. The present recipe merely gives some examples of using a WCS.

The recipe uses file ngc1275dss.sdf which is an image centred on the galaxy NGC 1275 extracted from the DSS. It will be very similar to the image that you created in the recipe in Section , and you could substitute your own image if you prefer.

Load file ngc1275dss.sdf into GAIA and adjust the colour table so that you can see the stars and galaxies. The display should look something like Figure .