What is Parallax?
Copyright © 2009 All Rights Reserved
by David Cochrane
Parallax is a huge issue that astrologers generally don't pay much attention to. I'll go over all this from the group up so we don't miss anything.
Parallax arises from the different points from which which two observers view an object. A simple example of parallax in our everyday lives provides an easy way to understand what parallax is.
An example of parallax is this: Two people are standing 30 feet apart and are looking at the same object 50 feet away. When each of the two people points to the object, an imaginary line drawn from person A to the object and an imaginary line drawn from person B to the object are not parallel. The object is in a different place relative to the background.
Measuring parallax: The closer the object is relative to the distance between the people, the greater is the angle of the two yellow lines in the diagram where they meet at the object being viewed. This angle is a measure of parallax. As the object is moved farther away, parallax decreases and at an infinite distance becomes zero. Note, however, that size of parallax depends on two things: the distance by which the two observers are separated and the distance of the object being viewed. Note that given the distance between two people and the angle of parallax, the distance of the object can be determiend so parallax can be used to determine the distance of an object. To do this, we need two points of viewing the object and a background to reference where the object is from these two points of view.
There are two basic kinds of parallax in astronomy that are relevant to astrology, and I describe them below:
Parallax is a big issue. It is possible that astrologers are using an incorrect position of the Moon by not using the parallax-corrected Moon position. In research that I have done in the past amazingly the parallax-corrected Moon seemed to not work as well as the plain old Moon and this surprised me. I suspected that the parallax-corrected Moon would be more accurate because it is the position of the Moon from the person's point of view. In a birth chart it is where the Moon is if one looks up at the night sky. The research that I have done or that anyone else has done up to this point in time is not definitive. There are no research studies that clearly and unambiguously support astrological theories, so we are still at a stage of building models, gathering anecdotal evidence, and doing exploratory research.
The parallax-corrected Moon affects everything that an astrologer may interpret: the birth chart, forecasts, AstroMaps, etc. The parallax-corrected Moon is simply at a different position than the usual Moon, and, as noted above, is up to about one degree different in its placement.
The elevation of a place from sea level also has an effect on parallax. At the top of a mountain parallax is greater than at sea level. The difference in elevation can change the parallax-corrected position of the Moon by up to a few minutes of arc.
Note that there are other important issues that are also regarded as unimportant by astrologers, such as refraction of light and the speed of light, for example. These topics can be addressed in a separate article in the future.
AUTHOR: David Cochrane