Rapt parallel and mundane parallel

Meaning

In the Placidian tradition of primary directions, two planets can be linked by equal proportional distance from the cardinal angles (MC, IC, ASC, DSC), measured in units of each planet's own diurnal or nocturnal semi-arc (DSA and NSA) [1][4]. Unlike a zodiacal aspect (measured in ecliptic longitude λ) or a declination parallel (equal distance north or south of the equator δ), a mundane parallel or rapt parallel is a pure symmetry of temporal motion in the local sky.

Let each body's proportional meridian fraction be f = MD / SA, where MD is its equatorial Meridian Distance from the MC (or IC) and SA is its active semi-arc (DSA above the horizon, NSA below). Two bodies stand in mundane parallel whenever their proportional distances from one of the four cardinal axes (MC, IC, ASC, DSC) are equal on opposite sides of that axis.

Natal Mundane Parallel vs. Rapt Parallel (Raptus Primi Mobilis)

Placidus distinguishes two ways this semi-arc symmetry occurs in primary directions [1]:

1. Direct / Converse Mundane Parallel (Mundane Parallel): One body (the significator) keeps its natal proportional distance |f_S| from the meridian or horizon, while the second body (the promissor) is carried by diurnal rotation until its own proportional semi-arc distance sits at the exact mirror distance −f_S on the opposite side of the angle (or at the identical distance +f_S).

2. Rapt Parallel (Rapt Parallel, Raptus Primi Mobilis): Neither body stays fixed at its natal place. Instead, the entire sky rotates westward after birth ("rapt", i.e. seized or swept along by the Primum Mobile), carrying both the significator S and the promissor P simultaneously until, at a single equatorial rotation angle ΔRAMC, the two bodies stand at equal proportional semi-arc distances on opposite sides of the MC, IC, ASC, or DSC [1][2]:

   f_S(RAMC_0 + ΔRAMC) + f_P(RAMC_0 + ΔRAMC) = 0 (about the Meridian)

   Taking SA_S and SA_P as the active semi-arcs of the two bodies, the exact equatorial arc ΔRAMC at which the Primum Mobile sweeps both planets into rapt symmetry around the upper meridian is solved closed-form by weighted harmonic interpolation of their right ascensions:

   ΔRAMC = [ SA_P · (α_S − RAMC_0) + SA_S · (α_P − RAMC_0) ] / (SA_S + SA_P)

Interpretive Force

Placidus (1657) [1] and John Partridge (1693) [2] regarded rapt parallels to the Sun, Moon, or angle rulers as among the most potent directions in a nativity—equal in force to a bodily conjunction or opposition—because both bodies are actively carried by the diurnal sphere into simultaneous dynamic equilibrium across the local meridian or horizon.

In Moira's Primary Directions Observatory, Section 03 · Rapt Parallels, Mundane Parallels, Antiscia & Royal Fixed Stars computes and displays every Mundane Parallel, Rapt Parallel (with its exact axis MC, IC, ASC, or DSC), Antiscia / Contra-Antiscia perfection, and full-3D Fixed Star hit in an interactive, sortable ledger.