Celestial Coordinates Toolbox

This window is designed to allow you to modify your image's celestial coordinate system. The choices available cover: FK5, FK4, FK4 with no E terms, Ecliptic, Galactic, SuperGalactic and Horizon coordinates (AzEl), just choose the system that you are after using the "System:" menu button and qualify it with an appropriate equinox and epoch, if necessary.

To apply the new system to the image press the "Test" button. This will make the sky coordinate position readouts change, and any grid overlay (although you can modify the coordinates that a grid is plotted in using methods in the grid plotting window). To make the change permanent press the "Accept" button and save the image to disk.

Note this window's effects are not related to those of "Built-in coordinates..." window. That selects from the systems already associated with your image, this window adds a new system by transforming from any existing celestial coordinates (so some celestial coordinates must already be available).

The "Ref point:" value is a specialist option and controls how a offset coordinate system is interpreted. See the descriptions of the attributes "SkyRefIs", "SkyRef" and "SkyRefP" in SUN/211.

The observer longitude and latitude are only used for Horizon coordinates. Both values are in degrees, with the longitude measured positive eastwards. In addition to decimal degrees the value may be formatted as in the following examples: "155:19:23.2", "155 19 23.2", "155:19.387", "155.32311", "E155.32311", "-204.67689", "W204.67689". As indicated, the sign of the longitude can optionally be indicated using characters "E" and "W" in place of the usual "+" and "-".

If you suspect that some of the meta-information which is used as part of the current celestial coordinate system is invalid, or may be causing some unintended side-effects, then you can opt to use a "New system", which creates a coordinate system that only has the values shown in this interface. Note that selecting this option will lose the sky reference position, so the "Ref point:" values will be ignored.