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

directed, the evening amplitude is called northern (septentrionalis); however, if the star were to set at S, such that OS were turned from O toward the south original: "Mittag", the evening amplitude would be called southern (meridionalis). One easily sees that the stars in the northern hemisphere AOQP have a northern evening amplitude, whereas those in the southern hemisphere AOQp have a southern evening amplitude.

In order to find the evening amplitude OS of a star, its distance from the equator DS, or its declination, must be given, along with the equator's height above the horizon of the place, which is equal to angle O. Then, in triangle ODS:

sin O : sin DS = sin tot : sin. OS

where OS is northern or southern, depending on whether DS is the one or the other. For sin. tot = 1, this gives the formula:

sin. Declination sin. Evening Ampl. = —————————————— cos. Latitude

By means of this formula, one can calculate a table in which one can look up the corresponding evening amplitude for the latitude of any place and the declination of any star, which can be found in the Berlin Collection of Astronomical Tables (Vol. III, p. 255) under the title: Table for the Amplitudes in East and West.

For Leipzig, whose latitude is 51° 19' 41'', one finds the evening amplitude of the sun on the longest and shortest days (where the declination amounts to 23° 28' 8'') = 39° 35' 39''. On the days of the equinoxes, however, the sun's evening amplitude = 0.

The calculation of the sun's evening amplitudes is especially useful to sailors for observing the deviation of the magnetic needle.

Aberration of light, Aberratio lucis, Aberration de la lumiere.

An apparent movement of the stars, by virtue of which they appear to traverse a small ellipse annually in the sky, the major axis of which amounts to 20 seconds of a great circle.

This remarkable phenomenon was discovered by James