The great disk of the galactic plane spins in space through time and carries with it all objects, including our Sun. Differential rotation causes objects that are located at different distances from the center of the galaxy to rotate at different speeds. In general, different groups of objects of a similar kind tend to move together through space. For instance, the Local System of stars that includes our Sun is moving in the general direction of the star Vega in the constellation Lyra. This apparent direction is termed the Solar Apex or Apex of the Sun's Way. The position given in astronomy books for the solar apex depends upon what group of stars we use to measure our Sun's motion. This can lead to a lot of confusion as to, which of several values is significant for our use.

Solar motion is often explained as the deviation of the Sun's motion from a circular motion around the GC. This definition may help to clarify some of the confusion surrounding the use of the solar apex in astrological work. The standard solar motion (listed below) is the sun's drift with respect to the stars, which form the majority in the general catalogue of radial velocities and proper motions (A to G main-sequence stars, giants and super giants) and not the right-angle motion of the Sun and other galactic objects around the galactic center. The solar apex value depends upon what group of background stars we use to measure our Sun's motion and the more distant the objects (such as globular clusters), the more this apex approaches a simple right-angle to the GC. In fact, if we remove the effect of solar motion, the Sun and nearby stars are found to be moving at right angles to the GC.

Astronomers do this to arrive at a value called the local standard of rest. The local standard of rest is arrived at by removing what is termed the basic solar motion, and this motion is defined as the most frequently occurring velocities in the solar neighborhood, the "average" of local stars as measured from their geometric centers, rather than their centers of mass. Centers of mass for individual stars are not known. Therefore, the apex of the Sun's way (by definition) cannot be derived from the more distant stars, but should be determined using relatively near stars since it is a measure of the Sun's drift with respect to the centroid of motion of the local group of stars. It is similar to the slow drift to the side that often occurs to powerboats as they plow through the water. Astrologers will be interested both in the solar apex and in the right-angled motion of our Sun about the GC.

Copyright (c) 1997-99 Michael Erlewine