NOVELTY - Tracking apparatus (A1) comprises: support structure (20) mounted on support surface and having first center of mass; tracking assembly (22) rotatably coupled to support structure about first axis and having second center of mass; and payload assembly (24) rotatably coupled to tracking assembly about second axis transverse to first axis and having third center of mass. The payload assembly comprises at least one solar module, where net gravitational moment results from gravitational forces acting on first center of mass, second center of mass, and third center of mass about overturn axis.    USE - The tracking apparatus is useful: as celestial tracking apparatus for tracking celestial objects; and in two axis solar energy collection systems.    ADVANTAGE - The tracking apparatus resists overturning forces due to wind in part through gravitational forces acting on the moving elements of the structure, thus reducing or eliminating the need for a massive ballasted or dug-in foundation and reducing the total cost of installation.    DETAILED DESCRIPTION - Tracking apparatus (A1) comprises: a support structure (20) mounted on a support surface and having a first center of mass; a tracking assembly (22) rotatably coupled to the support structure about a first axis and having a second center of mass; and a payload assembly (24) rotatably coupled to the tracking assembly about a second axis transverse to the first axis and having a third center of mass. The payload assembly comprises at least one solar module, where a net gravitational moment results from gravitational forces acting on the first center of mass, the second center of mass, and the third center of mass about an overturn axis. The magnitude of a contribution to the net gravitational moment from the second center of mass and the third center of mass is greater than the magnitude of a contribution from the first center of mass. INDEPENDENT CLAIMS are also included for:    (1) a tracking apparatus (A2) comprising a tracking assembly having a first center of mass and configured to rotate about an azimuth axis, and a payload assembly comprising at least one device configured to interact with electromagnetic energy, where the payload assembly is mounted on the tracking assembly and configured to pivot about a pivot axis transverse to the azimuth axis, and the payload assembly has a second center of mass, where the first center of mass and the second center of mass are at or near the azimuth axis; and    (2) a tilt-roll tracking apparatus comprising a support structure mounted on a support surface, a concrete tilt structure rotatably coupled to the support structure about a horizontal tilt axis, a roll structure rotatably coupled to the concrete tilt structure about a roll axis transverse to the horizontal tilt axis, and a payload assembly coupled to the roll structure, where the payload assembly comprises at least one device configured to interact with electromagnetic energy.    DESCRIPTION OF DRAWING(S) - The figure shows a rear perspective view of an azimuth-elevation style two axis tracking apparatus.    Support structure (20)    Tracking assembly (22)    Payload assembly (24)    Azimuth structure (34)    Elevation structure (36)