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Figure 6.1 shows a contour plot on an Aitoff projection of the
celestial sphere representing the (logarithmic) exposure time (in seconds) of
the ROSAT all-sky survey. The spring equinox is located at the center of
Figure 6.1
, with increasing right ascensions plotted to the left.
The lowest contour indicates an (unvignetted) exposure of 250 s, and
each new contour represents an exposure increase by a factor of two.
Unshaded areas indicate regions with exposures of less than 250 s.
As is obvious from Figure 6.1
, such regions are of extremely
limited extent. The exposure time increases sharply
towards the poles of the ecliptic with relatively large latitudinal
exposure variations present, especially at southern latitudes.