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The IAU is talking about changing its definition of "planet" - or, more correctly, actually creating a firm definition of "planet" in the first place because until now it hasn't really been all that clearly defined - and that has raised some interest in the astrology of the potential new planets. I'd like to emphasize, for readers who aren't familiar with how astrology works, that what the IAU decides doesn't really have any direct bearing on astrological practice; astrologers will follow their own traditions and the definitions used in astronomy aren't really part of those. That's why the old canard about the astrological signs not corresponding to the astronomical constellations, falls apart under examination - both are precisely and accurately defined ways of describing locations in the sky, but they aren't identical to each other because they were designed for completely different purposes. However, even though astrologers don't need the IAU to determine what will or won't be astrologically important, the recent public attention to relatively newly-discovered solar system bodies seems like a good opportunity to look at the astrology of new planets.
Under the IAU proposal, the three planets to add immediately are Ceres, 2003 UB313 (which has been popularly named "Xena"), and Charon. Note that throughout I'm talking about Charon, the moon or companion of Pluto, not Chiron, the Centaur-type object already widely used in astrology. Of those three, Ceres is already widely used in astrology and we think we know what it means. I'd welcome raising it to first-class planet status because in my own symbolic system, I view it as being about mothers in the same was Saturn is about fathers, so it'd make for a nice symmetry. The object 2003 UB313 doesn't have much astrological work done on it yet, but there is some, and it at least is a relatively well-behaved object with an orbit that looks like a planet's orbit and so on. I'm reasonably confident that the community can figure out a sensible way to deal with 2003 UB313.
But Charon is another story. First of all, it'll always appear within a second of arc of Pluto, so if you just plot its position on a horoscope the way you would with some other planet, there's no real distinction you can draw between it and Pluto. Eric Frances has an interesting article that touches on this, though he seems to be confused about why Pluto-Charon would be a double planet when, for instance, Earth-Moon isn't. The reason for that is actually quite simple: it's because Charon is so big and close (relative to Pluto) that the centre of mass of the Pluto-Charon system is at a point somewhere between them, not inside either body. So it would be more accurate to say that Pluto and Charon orbit each other rather than Charon orbiting Pluto. That is not true of Earth and its Moon - the Earth-Moon centre of mass is well inside Earth, even though the Moon is very big and causes a significant perturbation of Earth's orbit.
The Eric Frances article suggests that if we treat Pluto-Charon (located at the same spot on the chart we've previously been calling "Pluto") as a double planet, that means we should recognize Pluto as having a "double nature". That's fine as far as it goes, but I don't see it as really making much difference; it's just a hairsplitting distinction in how we interpret the same factor we've already been using for decades. If Pluto and Charon are really going to be treated as first-class planets, I want to give them some separate identity, beyond just pointing to one chart location and saying "that's both of them".
He also goes into some discussion of the mythology, suggesting that Minerva or Bacchus might be good handles for the "other side" of Pluto. They might indeed, if only to reduce the confusion between Charon and Chiron. Unfortunately, there are already named asteroids (the name "minor planet" is apparently planned to be retired) called 2063 Bacchus and 93 Minerva. There's no other Charon, even though there's a Chiron, so at the moment, I think Charon seems least ambiguous. See also Axel Harvey's article on Lilith/Charybdis. I'm not sure I would go quite so far as to say that the name doesn't matter and we should only look at astrological research in determining meaning, though; I'd rather say that I think because of the way humans are, it's likely that whatever name finally sticks will be one that has an appropriate meaning.
If we want to include Charon in horoscopes as an object in its own right, not just a second meaning for the point labelled "Pluto", I think the way of doing it that makes most sense is to find the direction, not the location, of Charon as seen from Pluto, and plot that direction on the Earth-based astrological chart the same way we plot the direction of Luna's North Node. I'd also - and this is important for reasons I'll get into - include a time correction for the light-speed delay from the Pluto-Charon system to Earth. To illustrate my proposal, here's a narrative:
Shortly before you were born, an observer located at the centre of Pluto looked at Charon and determined its apparent direction as a vector with respect to the J2000 inertial reference frame (basically, the fixed stars). The observer then sent that vector as a radio message. It arrived at Earth at the same time you were born, and that same direction, plotted on the zodiac as if it were a vector relative to the centre of the Earth, is your Charon position.
The main reason for using the position of Charon seen from Pluto instead of seen from Earth, is simply that the position of Charon seen from Earth isn't interesting - it would always be pretty much the same as the position of Pluto seen from Earth. That can be made consistent with the rest of an astrological chart if we say that instead of viewing everything from Earth, we really view satellites of the Sun from Earth and satellites of other bodies from their primaries - so the Moon from Earth, Charon from Pluto, and other moons if we were going to use them, from their respective primaries. That does create a new inconsistency in that maybe satellites of the Sun should be viewed from the Sun instead of from Earth, but still feels okay to me. And maybe satellites of the Sun actually should be viewed from the Sun; there is an heliocentric astrology and it does make some sense.
On the light-speed correction, which may be the most controversial part of this proposal: I think that ideally, the things we plot on the chart should bear some resemblance to things we could at least in theory observe with a telescope. With the light-speed delay as I propose it, the Pluto-Charon vector is the one you'd see if you could point say the Hubble telescope at the Pluto-Charon system and infer their orientation from what you saw. You wouldn't see Pluto and Charon as they really were at the moment you looked; you would see them as they were about 5 hours before you looked, because of the light-speed delay. It makes sense to me that what should go on the chart should be what you see, not what in some abstract sense "really" exists. Under the theory of relativity, that kind of "reality" is a bit hazy anyway (no objective time); any physical influence PLuto and Charon could exert on Earth would have to be similarly delayed if it propagated in the way that all known physical forces propagate; and we already use apparent, not geometric, positions for plotting everything else on an astrological chart - including, and especially, the position of the Pluto-Charon system itself.
It's important to know for sure whether we want to use the light-speed delay or not, because it makes a huge difference - much more so than in any other case I'm aware of. If you ignore the light-speed delay in plotting, say, the position of Neptune, it only makes a difference of a few minutes of arc. Everything that's far enough away for the time delay to be significant, is also slow-moving enough that it doesn't matter much. But Charon is special because Charon is extremely fast as well as very far away. The orbital period of Pluto and Charon around each other is only 6.4 days! That's 2.3 degrees per hour, measured around the nearly-circular orbit; it will actually be even faster around the zodiac in some parts of the orbit, because the orbital plane is highly inclined. So using, or not using, the 5-hour correction means getting totally different astrological answers.
Someone could ask, if Pluto and Charon are both going to be treated as first-class planets, doesn't it make as much sense to use the apparent location of Pluto seen from Charon, instead of Charon seen from Pluto? Maybe it does. The apparent location of Pluto seen from Charon would be exactly opposite Charon seen from Pluto, so it costs nothing to plot a second point 180 degrees away on the chart. Maybe it should be viewed as an axis the same way we view the Earth's Moon's North and South Nodes.
Talking of nodes, the Pluto-Charon system has nodes and apsides just like the Earth-Moon system. Maybe the North Node of Charon, and the apoapsis of Charon (equivalent to Lilith/Charybdis for the Earth-Moon system), are also worth looking at.
Then, of course, this same kind of calculation could also be done with any moon in the Solar System. Charon is special because it seems to also be in some sense a planet... but every so often people talk about giving astrological meaning to the moons of Jupiter and Saturn, for instance. This same kind of technique could be applied to them. It does seem to suggest, that if we're going to plot a lot of objects with respect to their primaries (Charon with respect to Pluto, Earth's Moon with respect to Earth, and so on) that then we should maybe start plotting the primaries with respect to the Sun instead of Earth. J. Lee Lehman's Ultimate Asteroid Book does talk a fair bit about the heliocentric positions of asteroids; maybe just making everything centered on the nearest bigger thing it orbits, would produce the most internally consistent system. But then it seems like we'd also have to switch to a sidereal zodiac, because the tropical zodiac is entirely based on the Earth's motion. All in all, there's a lot of potential for exploration here.
NEW: Here is an online ephemeris, to make the calculation easier. It's brand new and may still be buggy, but in limited testing it agrees with the method described below.
Here's my current procedure for getting an approximate location for Charon, with the definition I propose above. It is only an approximation - it neglects the lightspeed delay from Charon to Pluto (only a fraction of a second of time); nutation of Earth's axis; "aberration" due to the finite speed of light interacting with the motions of Earth, Pluto, and Charon, and the Solar System's motion through the galaxy; and it uses a first-order approximation for the lightspeed delay. I'm pretty sure that this should still give results accurate to within a degree or two, in the 1965-2049 date range for which NASA provides an ephemeris service. I've tested it to the extent I can, by applying the same calculation technique to other bodies in the Solar System and comparing the results with known good results from other sources. I don't have any "known good" results to compare to for Charon itself.
Before you start, here are the skills and tools you will need:
Note: you only need this if you're going to correct for light speed; otherwise, skip it and use your time directly for computing the Pluto-Charon vector. I think the light-speed correction is important for astrological validity, but depending on your point of view you might think it should not be done; see the discussion above. Be warned that you will get totally different answers depending on your stance on this issue, so you have to make up your mind one way or the other.
First, convert your chart time to whatever format your Pluto ephemeris needs. If you are using Swiss Ephemeris, you can use UTC and let the machine do the conversion to dynamical time. Example: my birthdate is August 1, 1976, time 10:22 PDT. Adding 7 hours for PDT, that is 17:22 UTC.
Find the geometric distance to Pluto for your chart time. You can do that with the Swiss Ephemeris test page. Use "9" in "planet selection" for Pluto, "PR" in "output format" for name and distance, and the options "-j2000 -true" for geometric distance in J2000 coordinates. You will also need to specify the time of day under "other options", using "-ut" if it's UTC or "-t" if it's dynamical "ephemeris" time. Example: I type "1.8.1976" into "start date", "9" into "planet selection", "PR" into "output format", and "-ut17:22 -j2000 -true" into "other options". Output below.
/ulb/swetest -b1.8.1976 -n1 -s1 -fPR -p9 -eswe -ut17:22 -j2000 -true date (dmy) 1.8.1976 greg. 17:22:00 UT UT: 2442992.223611 delta t: 47.077533 sec ET: 2442992.224156 Epsilon (true) 23°26'32.3733 Nutation 0° 0' 0.0000 0° 0' 0.0000 Pluto 31.067858046
Write down the distance to Pluto in astronomical units. If you're using Swiss Ephemeris, now is a good opportunity to start using dynamical-time Julian day numbers, shown as "ET", because that'll make later calculations easier. Example: my distance to Pluto is 31.067858046 au, and my dynamical time is 2442992.224156.
Divide the distance to Pluto by the speed of light, which is 173.1445988 au per day. The result is the light-speed delay, the number of days it took light from Pluto to reach Earth. Example: 31.067858046 au divided by 173.1445988 au per day is 0.17943302 days. I'm carrying excess precision in these calculations, but it's harmless.
Subtract the light-speed delay from the chart time to get the time of interest at the Pluto-Charon system. Example: 2442992.224156 minus 0.17943302 is 2442992.044723.
If you aren't already working with dynamical time, you must convert to dynamical time now, because HORIZONS requires it.
Visit the HORIZONS Web interface and start selecting options.
Under "Ephemeris type" select "Vector table".
Under "Target body", select Charon by typing "901" into the "Lookup" box and clicking "search", then choosing Charon in the list that appears and clicking "Select Indicated Body".
Under "Coordinate origin", select Pluto by typing "@999" into the "Lookup named location" box and clicking "search". Note the "@".
Enter your chart time, with light-speed correction if you're using it, as the start time for the query. If you have a Julian date, you can just type "JD (whatever)" into the start and stop boxes. If you don't, you can enter the dates and times in some other format, following the instructions on the page, but note that HORIZONS will not accept Universal time for this type of query, only dynamical time. Note that the difference is probably only about a minute of time or so anyway and could probably be safely ignored. Note that notwithstanding the instructions on the HORIZONS Web page, you must not enter any spaces in the time specification! Example: I enter "JD2442992.044723" for start time.
Enter a time one day later for the stop time - you only care about one emphemeris entry, but the HORIZONS system requires entering a time range and I haven't been able to figure out how to make it give just one entry of output. Example: I enter "JD2442993.044723" for stop time.
You want J2000 geometric positions referenced to the ecliptic and mean equinox of the reference epoch, using au as the units of measurement; those are the defaults and don't need to be changed.
Click "Generate Ephemeris" and find the X,Y,Z coordinates corresponding to your chart time. Note that these numbers are in scientific notation with "E" used to mark the power of ten. They represent Charon's position in J2000 coordinates. Example: partial output below.
******************************************************************************* JDCT X Y Z VX VY VZ LT RG RR ******************************************************************************* $$SOE 2442992.044723000 = A.D. 1976-Aug-01 13:04:24.0672 (CT) -4.109794481230587E-06 -7.231615924817409E-05 -1.093026914882060E-04 -9.449245654436223E-05 -7.142983909740253E-05 5.050293099710607E-05 7.573110981488223E-07 1.311243519169920E-04 2.575410985267728E-07 2442993.044723000 = A.D. 1976-Aug-02 13:04:24.0672 (CT) -8.232529082224226E-05 -1.006876869663091E-04 -1.795320908069566E-05 -4.920537034822100E-05 1.925792593165510E-05 1.172479785594147E-04 7.582835816335340E-07 1.312927322127443E-04 5.204349567048787E-08 $$EOE *******************************************************************************
My X,Y,Z coordinates are X=-4.109794481230587E-06, Y=-7.231615924817409E-05, Z=-1.093026914882060E-04.
Compute the arctangent of Y/X in degrees, using 90 if X=0 and Y is greater than 0, or 270 if X=0 and Y is less than 0. Then add 180 if X was negative. Add or subtract 360 if needed to bring the result into the range 0 to 360. What's left is the longitude of Charon in degrees in the J2000 reference frame. Example: -7.231615924817409E-05/-4.109794481230587E-06 = 17.5960524; atan 17.5960524 = 86.7473264; but X was negative, so add 180 to get 266.7473264.
NEW: Correcting for precession of the equinoxes is probably unnecessary if you're working with dates in the range handled by HORIZONS, but to really get it right, subtract the Julian day number (at Earth, no lightspeed correction) from 2451545.0, divide by 26141.153, and subtract the result from the longitude. Example: 2451545.0-2442992.224156 is 8552.77584, divided by 26141.153 is 0.327177, subtract from 266.7473264, the result is 266.420497.
Divide the longitude by 30 degrees into a whole number result and a remainder. Count the whole number result as a number of signs after Aries (not counting Aries) to find the sign of Charon. The remainder is the degree within the sign, which you can convert to degrees, minutes, and seconds if you wish - though at this point you might as well round off to a whole degree anyway. Example: 266 divided by 30 is 10 remainder 26. Aries(0), Taurus(1), Gemini(2)... my Charon position is 26 Sagittarius, which happens to be right on top of my IC.
Now figure out what it means.
There's my proposal on how to calculate an astrological factor for Charon, but I still have very little idea on what meaning should be assigned to it. That's an astrological research question. I note that Charon, calculated this way, will tend to move very fast, much faster than any other objects in the horoscope and roughly in the same range as things like the Ascendant. That seems to make it a very personal kind of indicator, which makes the connection to distant, impersonal Pluto-Charon as seen from Earth (the indicator we've been calling Pluto all this time) all the more interesting. I'd encourage you to write to me or post comments with the comment form below if you have ideas on what Charon ought to mean, what's the best way to define it, whether you'd be interested in free Linux-based software or a Web page calculator for computing it, whether you'd want to buy an ephemeris printed as a book, any ideas on an appropriate astrological glyph for Charon, similar computations for other moons, etc.
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