prime vertical

noun

1. astronomy the great circle passing through the observer's zenith and meeting the horizon due east and west

Example Sentences

The amplitude of a star is its distance from the prime vertical, measured on the horizon, north or south.

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The transit instrument is also used in the prime vertical for the determination of latitudes.

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The method of determining latitude by transits in the prime vertical has the disadvantage of being a somewhat slow process, and of requiring a very precise knowledge of the time, a disadvantage from which the zenith telescope is free.

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R�mer, on the other hand, deserves full credit for originating the transit-circle and the prime vertical instrument; and he earned undying fame by his discovery of the finite velocity of light, made at Paris in 1675 by comparing his observations of the eclipses of Jupiter’s satellites at the conjunctions and oppositions of the planet.

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In 1862 Professor Hubbard began a series of observations of α Lyræ at the Washington Observatory with the prime vertical transit instrument, for the purpose of determining the constants of aberration and nutation and the parallax of the star.

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