Dictionary of Physics or an Attempt at an Explanation of the Most Important Concepts and Technical Terms of Natural Philosophy

this moment constitutes the difference between the altitude of the star and the altitude of the equator in the meridian. If the latter is known for the place of observation (see Equator Altitude), then, when subtracted from the meridian altitude of the star, the deviation of the same remains, e.g.

Meridian altitude of the sun
at Paris on June 21, 1738: 64° 38' 10" (Cassini, Elem. Astron. L. II. ch. 4)
Equator altitude of Paris: 41° 9' 50"

Deviation of the sun: 23° 28' 20" northern.

If the meridian altitude of the star is smaller than the equator altitude, a negative or southern deviation remains.

Astronomers have found the deviations of most fixed stars through frequent observations of meridian altitudes and entered them into fixed star catalogs (Catalogos fixarum). From the right ascensions and deviations of the stars, their longitudes and latitudes can be calculated; and this method, brought more into use by Tycho de Brahe, is easier and safer than a certain procedure of the ancients, who sought longitudes and latitudes directly through observations. Tycho introduced the quadrant fixed in the meridian plane (wall quadrant, quadrans Tychonius) to determine meridian altitudes.

The deviation of the sun is northern in our countries in spring and summer, and southern in autumn and winter. On the days of the equinoxes (March 21 and Sept. 21), it is = 0; on the days of the solstices (June 21 and Dec. 21), however, it is at its greatest and equal to the obliquity of the ecliptic, i.e., currently 23° 28' 8" (see Obliquity of the Ecliptic). One calculates the deviation of the sun for every day of the year from the obliquity of the ecliptic and the place or longitude of the sun through the formula

sin. deviation = sin. obliquity of the ecl. X sin. longitude of the ☉

Through this, tables can be calculated in which one can find the deviation of the sun for every point of its path through