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  2. Printing registration - Wikipedia

    en.wikipedia.org/wiki/Printing_registration

    When printing an image or a package of some sort that has more than one color, it is necessary to print each color separately and ensure each color overlaps the others precisely. If this is not done, the finished image will look fuzzy, blurred or "out of register" (see image to right).

  3. Polar alignment - Wikipedia

    en.wikipedia.org/wiki/Polar_alignment

    In the Northern Hemisphere, rough alignment can be done by visually aligning the axis of the telescope mount with Polaris.In the Southern hemisphere or places where Polaris is not visible, a rough alignment can be performed by ensuring the mount is level, adjusting the latitude adjustment pointer to match the observer's latitude, and aligning the axis of the mount with true south or north by ...

  4. Setting circles - Wikipedia

    en.wikipedia.org/wiki/Setting_circles

    Also, even the finest graduations on setting circles are usually more than a degree apart, which makes them difficult to read accurately, especially in the dark. Nothing can be done if the optical tube is not perpendicular to the declination axis or if the R.A. and Dec axes are not perpendicular, because these problems are next to impossible to ...

  5. Equatorial mount - Wikipedia

    en.wikipedia.org/wiki/Equatorial_mount

    German equatorial mount. In the German equatorial mount, [4] (sometimes called a "GEM" for short) the primary structure is a T-shape, where the lower bar is the right ascension axis (lower diagonal axis in image), and the upper bar is the declination axis (upper diagonal axis in image).

  6. Spherical coordinate system - Wikipedia

    en.wikipedia.org/wiki/Spherical_coordinate_system

    Once the radius is fixed, the three coordinates (r, θ, φ), known as a 3-tuple, provide a coordinate system on a sphere, typically called the spherical polar coordinates. The plane passing through the origin and perpendicular to the polar axis (where the polar angle is a right angle) is called the reference plane (sometimes fundamental plane).

  7. Axial precession - Wikipedia

    en.wikipedia.org/wiki/Axial_precession

    The term "precession" typically refers only to this largest part of the motion; other changes in the alignment of Earth's axis—nutation and polar motion—are much smaller in magnitude. Earth's precession was historically called the precession of the equinoxes , because the equinoxes moved westward along the ecliptic relative to the fixed ...

  8. Universal polar stereographic coordinate system - Wikipedia

    en.wikipedia.org/wiki/Universal_Polar...

    The universal polar stereographic (UPS) coordinate system is used in conjunction with the universal transverse Mercator (UTM) coordinate system to locate positions on the surface of the Earth. Like the UTM coordinate system, the UPS coordinate system uses a metric-based cartesian grid laid out on a conformally projected surface.

  9. Duality (projective geometry) - Wikipedia

    en.wikipedia.org/wiki/Duality_(projective_geometry)

    The line p through Q which is perpendicular to the line OP is called the polar [22] of the point P with respect to circle C. Let q be a line not passing through O. Drop a perpendicular from O to q, meeting q at the point P (this is the point of q that is closest to O). The image Q of P under inversion with respect to C is called the pole [22] of q.