Title:

An examination of the difficulty of an accurate determination of the time at which a planet’s motion becomes stationary. This has relevance to the timing of the coming conjunctions of Uranus and Neptune.

In 1978, in the "Ephemeris of Chiron," [James Neely and Erik Tarkington, Phenomena Publications, distributed by Samuel Weiser, Inc., P.O. Box 612, York Beach, ME 03910.] Erik Tarkington remarked that, "The calculation of stations is tremendously insensitive to time in amounts on the order of a few minutes or hours. In 1/100 of a day immediately after station, Chiron typically moves about 8/100,000,000 of a degree. This means that we must know Chiron's position to the nearest 8 x 10-8 degree in order to specify the actual time of station to within 0.01 of a day, and 0.01 of a day equals about 15 minutes!" This is a major reason why different programs can generate very accurate positions for astrological work, but can disagree radically on the time of occurrence of a planetary phenomenon.

Since I have access to the state of the art ephemeris (the DE-200 integration computed by the Jet Propulsion Laboratory), I thought that it would be interesting to compute a table showing how long it takes each planet to move a discernible amount from its station.

First, I generated a table of the time of occurrence and position of the retrograde and direct stations for each planet. Then I recorded the time duration in which the planet's position was indistinguishable from its station position, when rounded to the nearest 0".01, 0".1, or 1". These time durations for 1985 (1984 for Mars) are given in Table 1.

Table 1 – Planetary Time Duration at Stations (Rounded Positions)

An examination of Table 1…reveals that the duration of periods of indistinguishability is not as systematic as might be expected. In fact, it appears as though the table is in error for the 0".01 and 0".1 times at Saturn's direct station, and that there is a similar error for the 0".1 and 1" times at Uranus' direct station. This discrepancy turns out to be real, but yet is an artifact of the rounding mechanism which depends upon the planet's position. Table 2 provides details of times and positions at Saturn's station, where only the seconds and fractions of seconds of the direct position are shown in the table - for instance, an apparent ecliptic longitude of 231º 28'03".25 is displayed as 3".25.

Table 2 – Details of Saturn’s Direct Station (Rounded Positions)

Even though a column showing Saturn's position rounded to the nearest 0".001 has been added to Table 2, complete detail is still lacking. If, for example, at 19h02m the position were 3".2501, it would round to 3".250, 3".25 and 3".3, whereas if the position at 19h03m were 3".2499, it would round to 3".250, 3".25 and 3".2. From the table it can be seen that Saturn spends more time at 3".25 than it does at 3".2.

Although the duration times given in Table 1 are correct, they are subject to the rounding artifact mentioned above. To get a truer picture of the time on station, I decided to do a second series of computations to arrive at what might be called a "worst case" scenario. Again a table of positions at the time of station was examined. Then I recorded the time duration in which the planet's position varied by 0".01, 0".10, and 1".00 from the stationary position. For example, if the stationary direct position was 26".391, then I recorded the time duration in which the body was within 26".401 (+0".01), 26".491 (+0".10), and 27".391 (+1".00), of the stationary position. The results are given in Table 3.

Table 3 – Planetary Time Duration at Stations (Absolute Positions)

It should be emphasized that these tables were computed only for the station times at the date given and do not in any way represent an average time for any particular planet. Table 3 reveals that for outer planets, it is extremely difficult to generate an accurate station time and even the most accurate ephemeredes are not really to be trusted. Certainly station time can be computed accurately with respect to a given ephemeris, but how accurate is the ephemeris? The most accurate ephemeris currently available is DE200, but according to the "Astronomical Almanac," "A satisfactory ephemeris for Uranus for the 1980's could be computed only by excluding observations made before 1900." This should serve as a reminder that accurate ephemeredes are computed for the express use of astronomers for astronomical purposes and that astrologers must use the results as best they can. Since the DE-200 ephemeris covers the years 1800-2050 but ignores all observations of Uranus prior to 1900, one might ask how accurate is a Uranus station time for 1853? Our answer would be to calculate the station time and then look at Table 3 and decide that the station time might be correct to within ±19 hours.

Editor's note:
This article first appeared in the 1992 Summer edition of "Matrix Journal.

© Copyright: James Neely