Astro*Dictionary by Michael Erlewine

9 articles for "Arc"

Arc [Astro*Index]

The separation between two points as observed from a position of reference, expressed as the angle between the lines of sight drawn on the points from the reference position. Arc is measured in a number of different units designed for various purposes: radians, grads, revolutions or circles, hours, degrees, etc. The most common unit of arc in astronomy and astrology is the degree, of which there are 360 in a full circle. Degrees are assumed to be the arc unit throughout this work.

Arc [Munkasey M.]

An angular measure between two bodies.

Arc [DeVore]

A portion or segment of a curved line, such as a circle, or ellipse. Hence the orbital distance separating two bodies, or between two points.

Arc of Direction [Astro*Index]

An angular measurement used in various methods of direction. The arc of direction is calculated for the event in question and then added to the radix planet positions or the RAMC. The results are the directed positions which are then aspected to the radix planets. Solar arc is an arc of direction.

♦ Radix Method ♦ Directions ♦ RAMC ♦ Solar Arc
Arc of Direction [Munkasey M.]

An arc used in predictive Astrology.

♦ Radix Method ♦ Directions ♦ RAMC ♦ Solar Arc
Arc of Stature [Astro*Index]

The arc from the middle of the 1st house through the middle of the 8th house, passing through the 10th, is called the Arc of Increased Stature; it is said to peak at the cusp of the 12th house. The arc from the middle of the 7th house to the 2nd house, passing through the 4th house, is called the Arc of Dwarfed Stature; it is said to peak at the cusp of the 6th house. The Moon's ascending node is used as an indicator with respect to these two arcs.

♦ House Cusp ♦ Lunar Node ♦ Line of Advantage ♦ House System
Arc of Vision [Astro*Index]

The minimal angular distance from the Sun at which a planet is visible when the Sun is below the Horizon. The value depends on the planet's albedo, refraction, and atmospheric conditions.

♦ Angular Distance ♦ Albedo ♦ Refraction
Arc of Vision DeVore]

The least distance from the Sun at which a planet is visible when the Sun is below the horizon.

Diurnal Arc. The arc through which the Sun passes from sunrise to sunset. At the Equinox this arc is 180°, or 12 hours of right ascension. With increased latitude (distance away from the Equator) and nearness to the Solstices it becomes larger or smaller.

Nocturnal Arc. That portion of 360°, or 24 hours, which remains after subtracting the Diurnal Arc. Semi Arc. Diurnal and Nocturnal, Half of either the Nocturnal or Diurnal Arc, measured from the Midheaven or Imum Coeli to the horizon.

Arc of Direction. The distance between a significator and the point where it forms an aspect with a promittor, measured in degrees and minutes of the Equator; distance from the place of a planet to the body of same, or to a point where an aspect will be formed thereto. It may be measured either in Sidereal Time according to Tables of Ascension, or in Right Ascension as computed by spherical trigonometry. In primary directions this Arc is translated into time in the proportion of one degree of arc to a year of time, or five minutes of arc to one month of time. (v. Directions.)

♦ Angular Distance ♦ Albedo ♦ Refraction
Arc Transform Chart [Astro*Index]

Harmonic charts determined by the angular separation between any two planets in the chart. For example, an arc transform chart for the sun and moon with an angular separation of 22.25 degrees would be calculated at a harmonic of 16.17978 (22.25 x 16.17978 = 360). This chart is quite different from a 16th harmonic chart. The discrepancy between the positions of the two charts increases progressively as a function of zodiacal longitude.