The CVZ is defined by a cone that is roughly 12 degrees in half angle, centered on the vector that is perpendicular to the current orbital plane: one pointing generally north (i.e. the "N-CVZ"), and one pointing generally south (i.e. the "S-CVZ"). Targets inside these two cones are always far enough away from the limb of the earth through the entire orbital period so that they never become occulted. Therefore, viewing efficiency is much higher for targets when they are in the CVZ, and continuous phase coverage can be obtained during certain parts of the day.
FUSE's orbit is inclined 25 degrees relative to the equatorial plane, which means that the orbit plane normal vectors (the centers of the N- and S-CVZ) are 25 degrees away from the equatorial poles. Thus, the center of the CVZ is always at Dec=+/-65 degrees. The right ascenscion of the ascending node (RAAN) of FUSE's orbit precesses about the earth at approximately 6 degrees west per day, and the instantaneous RA of the N- and S-CVZ centers regresses at this rate as well.
Since the CVZ is roughly 12 degrees in half angle, any target in an annulus between 53°<Dec< 77° (in the north) or -77°<Dec<-53° (in the south) can potentially be in the CVZ at some point during the year. Exactly when depends upon the target's RA, and the RAAN of FUSE's current orbit. The CVZ plots from the FUSE Sky Plotting Tool help answer this question graphically. A quantitative answer can be found using the FUSE Continuous Viewing Zone and Orbit Ram Calculator.
The FUSE Sky Plotting Tool CVZ plots show the north and south regions on the sky where the CVZ could potentially be, shown in zenithal equal area projection; meridians of longitude are shown as dashed lines radiating outwards from the center, and parallels of latitude are concentric circles. Both N- and S-CVZ graphs are shown looking down from the north celestial pole.
The subsections of the sky whose beta angle (anti-solar angle) is greater than the nominal limit are shaded light red (gray if you're making a B&W printout). The actual CVZ is the small circle whose diameter fits inside each annulus.
For example, on 1 September 2000, the N-CVZ looks like:
and the S-CVZ looks like
