Boys start to get acne at the age of approximately 12 years, with a range of 9 to 15 years old. As most girls will attest, boys on average mature later than girls. Early on in the onset of teen acne, the main lesions are blackheads and whiteheads.
The angular size (angular diameter, apparent size) of an object as seen from a given point is the visual diameter of the object measured as an angle. The visual diameter is the diameter of the perspective projection of the object on a plane through its center that is perpendicular to the viewing direction.
This applies equally to the Earth rotating around the axis of the Sun and the center of the Milky Way Galaxy. This view of Earth comes from NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite. In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating.