Light, Velocity of. 186,270 miles per second.
Light-year. Unit of measurement of Ultra-solar system distances. A Light-year is the
distance light travels in one year - at the rate of 186,000 miles per second, or about six trillion
miles: 6 with 12 ciphers. Intra-solar system distances are measured in astronomical units. An
astronomical Unit is the mean distance of the Earth from the Sun, about 92,930,000 miles,
where it is found in April and October, at which time the Sun's light reaches the Earth in 499
seconds, or about 8 minutes. The inadequacy of this unit for ultra-solar system spaces can be
seen by comparing the Pluto distance from the Earth, of 39½ A.U., light from which reaches
the Earth in a little over five hours, with the distance of the next closest major body beyond
Pluto, the star Alpha Centauri, light from which requires 4.3 years to traverse the intervening
25 trillion miles. Yet, if anyone on Alpha Centauri, despite its relative closeness, were to
attempt to observe Pluto he would find it separated from the Sun by an arc of only 1", which
means that Pluto and all the planets would be merged into the glare of the Sun, and give the
appearance of an average star of the third or fourth magnitude.
Lights. A term frequently applied to the Luminaries (q.v.), the Sun and Moon as
distinguished from the planets.
Lilith. A name sometimes given to asteroid No. 1181, a minor planet, of magnitude 14.1. It is
too faint to be seen other than with the aid of a telescope. It is not a "dark moon," but a planet
that shines by reflected light from the Sun - as does the Earth. Lilith is mentioned in the
apocryphal writings, as the "other woman" in the original triangle that rendered the Garden of
Eden no longer a paradise.
Local Mean Time. Based upon the moment when the mean Sun crosses the Midheaven of
the place. Local Mean Time was almost universally used prior to the adoption of Standard
Time on Nov. 18, 1883, and in some communities it continued to be used for a long time
thereafter. v. Time.
Logarithms. Proportional parts of a quadrant, expressed in numbers, whereby calculations of
the planets' places at a given hour, or the Arc of Direction for a given date, can be made by
simple addition and subtraction rather than by multiplication or division. They were invented
in 1614 by Baron Napier of Murchiston for use in his astrological calculations. Tables of
Logarithms are in common use in all schools by students of trigonometry. Tables of natural,
proportional and logistic logarithms are also available, each designed for different uses. An
improvement in logarithms was introduced by Henry Briggs in 1624.