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When the rays are lines of sight from an observer to two points in space, it is known as the apparent distance or apparent separation. Angular distance appears in mathematics (in particular geometry and trigonometry) and all natural sciences (e.g., kinematics, astronomy, and geophysics).
This diagram shows various possible elongations (ε), each of which is the angular distance between a planet and the Sun from Earth's perspective. In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. [1] The greatest elongation is the maximum angular separation.
In this case the specific orbital energy is also referred to as characteristic energy (or ) and is equal to the excess specific energy compared to that for a parabolic orbit. It is related to the hyperbolic excess velocity v ∞ {\displaystyle v_{\infty }} (the orbital velocity at infinity) by 2 ε = C 3 = v ∞ 2 . {\displaystyle 2\varepsilon ...
Right ascension (abbreviated RA; symbol α) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the Earth. [1]
By subtracting this figure from 90°, he would find that the zenith distance of the Sun is 0°, which is the same as his latitude. If Observer B is standing at one of the geographical poles (latitude 90°N or 90°S ), he would see the Sun on the horizon at an altitude of 0°.
Hence the distance is greatest when looking directly away from the Sun along the horizon in the east, and lowest along the horizon in the west. The bottom plot in the figure to the left represents the angular distance from the observed pointing to the zenith, which is opposite to the interior angle located at the Sun.
A slow motion of Earth's axis, precession, causes a slow, continuous turning of the coordinate system westward about the poles of the ecliptic, completing one circuit in about 26,000 years. Superimposed on this is a smaller motion of the ecliptic , and a small oscillation of the Earth's axis, nutation .
This slightly greater orbital angular momentum causes the Earth–Moon distance to increase at approximately 38 millimetres per year. [17] Conservation of angular momentum means that Earth's axial rotation is gradually slowing, and because of this its day lengthens by approximately 24 microseconds every year (excluding glacial rebound). Both ...