Space Telescope Science Institute   7.8 Specifying Orientation on the Sky  7.9.1 Parallel Observing

7.8.1 Determining Orientation for Phase II


A particular orientation is specified in an HST Phase II proposal using yet another coordinate system: U2,U3. These axes are opposite to V2 and V3, so, for example, U3 = -V3. The angle ORIENT, used in a Phase II proposal to specify a particular spacecraft orientation, is the position angle of U3 measured from North towards East. The direction of the V3 axis with respect to North is PA_APER - y and so

ORIENT = PA_APER - y ±18.

The IRAF task rotate in the package images.geom takes an image and rotates it counter-clockwise by a specified angle. To orient an image so that its y axis becomes North, the angle to specify is PA_APER. The x axis will then point approximately 5º North of East. Orientations can be checked by using the Visual Target Tuner (VTT) in the APT.


 7.8 Specifying Orientation on the Sky  7.9.1 Parallel Observing
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