ellipse is the true shape of earths orbit.
ellipse is the true shape of earths orbit.
what is the true shape of earths orbit?
ellipse
the parallel projection (skew or orthographic) of a circle that is in general an ellipse (the special case of a line segment as image is omitted). a fundamental task in descriptive geometry is to draw such an image of a circle. the diagram shows a military projection of a cube with 3 circles on 3 faces of the cube. the image plane for a military projection is horizontal. that means the circle on the top appears in its true shape (as circle). the images of the circles at the other two faces are obviously ellipses with unknown axes. but one recognizes in any case the images of two orthogonal diameters of the circles. these diameters of the ellipses are no more orthogonal but as images of orthogonal diameters of the circle they are conjugate (the tangents at the end points of one diameter are parallel to the other diameter !). this is a standard situation in descriptive geometry:
rytz's construction
aside from the orthographic, six standard principal views (front; right side; left side; top; bottom; rear), descriptive geometry strives to yield four basic solution views: the true length of a line (i.e., full size, not foreshortened), the point view (end view) of a line, the true shape of a plane (i.e., full size to scale, or not foreshortened), and the edge view of a plane (i.e., view of a plane with the line of sight perpendicular to the line of sight associated with the line of sight for producing the true shape of a plane). these often serve to determine the direction of projection for the subsequent view. by the 90° circuitous stepping process, projecting in any direction from the point view of a line yields its true length view; projecting in a direction parallel to a true length line view yields its point view, projecting the point view of any line on a plane yields the plane's edge view; projecting in a direction perpendicular to the edge view of a plane will yield the true shape (to scale) view. these various views may be called upon to help solve engineering problems posed by solid-geometry principles
descriptive geometry