observer's meridian


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Noun1.observer's meridian - a meridian that passes through the observer's zenith
line of longitude, meridian - an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator; "all points on the same meridian have the same longitude"
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In about 8000 years, the earth's axis will be pointing directly at Deneb, and that star will no longer serve, as it did Ibn Majid, to indicate on crossing the observer's meridian the minimum position of the Pole Star at zero bashi, for it would then remain fixed on the observer's meridian wherever he might be standing in the Northern Hemisphere, while the Pole Star would be as far from the celestial pole as Deneb is now.
whose latitude remains constant as the star transits the sky from rising to setting; (b) the Colatitude, the angular distance between the Pole and the observer's meridian position; and (c) the Coaltitude, the angular distance between the observer and the Geographical Position.
It is quite obvious that for each rise or fall of the Pole Star by 1 isba, other stars on the observer's meridian would rise or fall by exactly the same amount, and this holds for the entire range of latitudes from Equator to poles.
Two abdal stars have equal altitudes and equal declinations when located symmetrically about the observer's meridian.
There is actually a very slow drift even for stars exactly abdal, and the further the stars are from the observer's meridian, the greater the variation and the smaller the range of latitude over which the method can be used.