The following is a brief description of the occulted telescope section of the UVCS. One side of the rectangular entrance aperture acts as a linear external occulter that shields the telescope mirrors from direct sunlight; the other sides serve to limit the amount of light entering the
Figure 2.1 Diagram of the UVCS instrument.
instrument.
For sun-center pointing the light from the solar disk enters a sunlight trap,
while coronal radiation from 1.2 
to 10 
illuminates three telescope mirrors.
The external occulter and the telescope mirrors are placed such that
radiation from 1.2 
just reaches the edges of the mirrors
and radiation from 10 
completely fills the mirrors.
The telescope mirror/internal occulter mechanism
tilts the three mirrors, allowing the coronal images to be scanned across
the entrance slits of the spectrometer assembly.
An internal occulter, just in front of the telescope mirrors, blocks light
diffracted and scattered by the external occulter that would otherwise be
imaged onto the slits and dominate the coronal radiation in many cases.
This internal occulter is translated across the mirrors as they tilt, so as to
cover those parts of the mirrors that would specularly reflect
the unwanted light through the slits.
The field-of-view (FOV) of the UVCS is illustrated in Figure 2.2.
When the center line and roll axis of the instrument is pointed at solar disk
center (as is done in most coronal observations), the Primary FOV of UVCS
extends from 1.5 to 10 
in the corona.
The Instantaneous FOV is the region of the corona which
is imaged onto the spectrograph entrance slits at a particular time.
For the EUV channels the Instantaneous FOV is a region at radial distance r
from solar disk center, with a length of 40 arcmin and a width determined by
the width of the spectrograph entrance slit. For the WLC the instantaneous
FOV is a region of 10 
10 arcsec located at the center of the
40 arcmin slice. The position r is determined by the angle of the telescope
mirror. The roll mechanism allows the telescope assembly to be rotated about
its axis, thus providing 360 degree coverage of the solar corona.
The FOV can be extended onto the solar disk by offset pointing
the instrument axis relative to sun center,
using the pointing adjustment mechanism.
Figure 2.2 Field of View of the UVCS EUV channels.