3 articles for "Semi-Arc"

**Semi-Arc**[Astro*Index]

The arc or portion of a body's daily travel between the *Horizon* and *Meridian*. It is measured along the *Celestial Equator*, and may be expressed in either arc- units (°'") or time-units (hms).

See also:

♦ Horizon ♦ Meridian ♦ Celestial Equator

**Semi-Arc**[Munkasey M.]

A term used in Primary Directions to denote the arc froma Significator to the Horizon or Meridian.

See also:

♦ Horizon ♦ Meridian ♦ Celestial Equator

**Semi-Arc**[DeVore]

That portion of a celestial body's apparent daily travel, during which it remains above the horizon, from its rising to its setting, is called its diurnal arc; hence half of the arc, from horizon to midheaven, is its **Diurnal Semi-Arc**. The other half, most of which is under the earth, is its nocturnal arc, and half of it becomes the **Nocturnal Semi-Arc**. The Sun's semi-arc, diurnal or nocturnal, when in 0° Aries or 0° Libra, is six hours or 90° all over the Earth. At other seasons the one is greater or less than the other, according to the time of the year and the latitude of the place. The greatest discrepancy occurs where the N. or S. latitude is high, and when the Sun is in 0° Cancer or 0° Capricorn. The semi-arc is usually measured in degrees of R.A. passing over the Meridian; although it can be expressed in terms of time.

See also:

♦ Horizon ♦ Meridian ♦ Celestial Equator

Astro*Index Copyright © 1997 Michael Erlewine