Latitude (Lat. latitudo, breadth).
I. In Geography, the distance of a place on the earth's surface from the equator, N. or S., reckoned in degrees, minutes, and seconds of the great circle constituting the earth's polar circumference. (See Degeee.) Technically expressed, the latitude of a place is its distance from the equator, measured by the angle which the horizon plane of the place makes with the earth's axis, or by the angle which a plumb line at the place makes with the plane of the earth's axis. It is therefore equal to the altitude of the pole of the heavens above the horizon. There are several ways of determining the latitude of a place. 1. The elevation of the pole star, corrected for the effects due to the star's motion round the real pole of the heavens, and for refraction, aberration, etc, gives the latitude.
2. The latitude may be determined by observing the altitude of a known star, when on the meridian; for manifestly the known north polar distance of the star added to the meridian altitude, corrected for refraction, aberration, etc, is the supplement of the altitude of the pole of the heavens, which altitude, as we have seen, is equal to the latitude of the place of observation. 3. If the altitudes of circum-polar stars above and below the pole be observed, the mean of these altitudes (corrected for refraction, aberration, etc.) is the altitude of the pole; that is, is the latitude. 4. The latitude can be determined by an extra-meridional observation of a star at a known hour. For in this case we have: 1, the star's polar distance; 2, the zenith distance at the time (which is the complement of the observed altitude corrected for refraction, aberration, etc.); and 3, the hour angle. That is, we have two sides and an angle (opposite to one of them) of the spherical triangle which has for its angular points the pole, the zenith, and the star.
Hence we can determine the third side, which is the zenith distance of the pole, that is, the complement of the latitude. 5. If a star be observed when on the prime vertical, the latitude becomes known without an exact knowledge of the hour, which the preceding method requires. For then we have in the right-angled spherical triangle which has for its angles the star, the pole, and the zenith, two sides known, viz., the polar distance of the star and its zenith distance. The third side, as in the last case, is the co-latitude. This method is more exact in its results if the observation is made with a carefully oriented transit instrument, and the star observed during both the eastern and the western passage of the prime vertical. G. In Sumner's method, the altitude of a star is observed twice, a known interval of time separating the two observations. 7. The latitude of a star may be determined by observing the meridian altitude of the sun, the polar distance of the sun at the epoch of observation being known from the ephemeris for the year.
II. In Astronomy, the distance of a heavenly body from the ecliptic, measured by the arc of a great circle perpendicular to the latter, intercepted between the ecliptic and the body. The heliocentric latitude of a planet is its distance from the ecliptic, such as it would appear from the sun.