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The plane tangent to celestial sphere for extrasolar objects On the plane of reference, a zero-point must be defined from which the angles of longitude are measured. This is usually defined as the point on the celestial sphere where the plane crosses the prime hour circle (the hour circle occupied by the First Point of Aries ), also known as ...
The inclination of orbits of natural or artificial satellites is measured relative to the equatorial plane of the body they orbit, if they orbit sufficiently closely. The equatorial plane is the plane perpendicular to the axis of rotation of the central body. An inclination of 30° could also be described using an angle of 150°.
Denoted with the symbol Ω, it is the angle from a specified reference direction, called the origin of longitude, to the direction of the ascending node (☊), as measured in a specified reference plane. [1] The ascending node is the point where the orbit of the object passes through the plane of reference, as seen in the adjacent image.
This is measured in the reference plane, and is shown as the green angle Ω in the diagram. The remaining two elements are as follows: Argument of periapsis ( ω ) defines the orientation of the ellipse in the orbital plane, as an angle measured from the ascending node to the periapsis (the closest point the satellite body comes to the primary ...
The user may choose to replace the inclination angle by its complement, the elevation angle (or altitude angle), measured upward between the reference plane and the radial line—i.e., from the reference plane upward (towards to the positive z-axis) to the radial line. The depression angle is the negative of the elevation angle.
The perifocal coordinate system (with unit vectors p, q, w), against the reference coordinate system (with unit vectors I, J, K) The perifocal coordinate (PQW) system is a frame of reference for an orbit. The frame is centered at the focus of the orbit, i.e. the celestial body about which the orbit is centered.
The origin is the Sun's center, the plane of reference is the ecliptic plane, and the primary direction (the x-axis) is the March equinox. A right-handed rule specifies a y-axis 90° to the east on the fundamental plane. The z-axis points toward the north ecliptic pole. The reference frame is relatively stationary, aligned with the March equinox.
Rays that leave the object with the same angle cross at the back focal plane. The front and rear (or back) focal planes are defined as the planes, perpendicular to the optic axis, which pass through the front and rear focal points. An object infinitely far from the optical system forms an image at the rear focal plane. For an object at a finite ...