The density of Tycho-2 stars on the sky shown in galactic
coordinates (panel a) and in equatorial coordinates (panel
b). Some of the dark features reveal low star density due to
nearby Galactic dust clouds, while other reveal variations in the
limiting magnitude caused by the scanning pattern of the
satellite. The densest areas have more than 350 stars
deg-2, while the thinnest have close to zero. The
average density varies from 25 stars deg-2 at
b=±90o and 50 stars deg-2 at
b=±30o to 150 stars deg-2 at
b=0o.
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