View Full Version : Newbie question

25-04-2010, 16:06
I've always wondered the method by which 'skywatchers' actually know where the planets are, is it just, 'eyes on' or is there a tool used in calculating their positions relative to the earth? I'm a bit confused as the closest thing to such a calculator I ever found was on Nasa's site that tells you the positions of the bodies of the sol system based on inputed dates.. its like a well guarded secret or something, can anyone enlighten me?

25-04-2010, 20:05
In the beginning, observation by direct skywatching was the only method of identifying planetary motion. By Babylonian times a body of written records based on observation, stretching back centuries, was used for prediction. These written records provided the basis for the next step - prediction from tables.

The Greeks applied complex mathematics to the process and developed theories of how planets moved, in time and space. These theories may not have been 'correct' by our modern standards but they provided a basis for refining a mathematical model of the solar system. Ptolemy provided a mathematics which was used up till the renaissance based on a geocentric view (though some Greeks had developed a heliocentric model). Ptolemy's model was used for the creation of ephemerides, tables giving the position of the planets with fairly good accuracy, though obviously it did not deal with the outer planets, asteroids or other bodies, which had not been discovered.

In the renaissance, Copernicus developed a model of heliocentric movement, based largely on the work of Arab Astrologer/Astronomers (which in turn can be traced back to Greek times). Refinements to the the theory of planetary motion came from Galileo and more importantly Kepler. Add in Newton's mathematics and you get a very precise means of predicting planetary position without ever having to look at the sky or through a telescope.

A mathematical model based on Newton and Kepler works very well for the prediction of planetary motion but not so well when you try to predict outside the solar system. Hence Einstein's theories provide modifications for much of NASA's modelling. Bigger and better computers, bigger and better telescopes allow for refinement but essentially you can predict using a PC and a mathematical model based on Newton's theory.

In practice you don't actually do this directly, you simply install the Swiss Ephemeris (or other ephemeris) on your PC, that contains the nescessary mathematical model and all you need to do is to ask for the positions at any given time on any given date. Virtually all Astrological software comes with an ephemeris 'built in' so the process never really impinges on the Astrologer any more.

I think it's still the case though that students learning Astrology have to master the use of an ephemeris and the calculation of planetary movement during the day, using two midnight positions from a hard copy ephemeris. Strictly speaking the mathematics is an approximation in that process but the error is so small it can be ignored,

26-04-2010, 08:18
Very detailed explanation, thanks for taking the time to outline that for me, I'll be looking up this 'ephimeres' calculator, do you have a link for any direct downloads for astrological software? also, is the moon included in these charts? if not, how hard of a time would I have including it or calculating it's position in relevant relation to the signs?

Also, a lil off the topic but, again, on topic as well

As the planets rotate around the sun, the spiral arm galaxy also rotates within the universe at large, the mayans had a calender wheel outside of the 'zodiac' wheel that depicted things we don't commonly associate with, well, anything. Could the mayans have been peering clean out of our galaxy and watching the rest of the universe and even understand the effects they have?

rough depiction

-- outside the spiral arm galaxy --
0000-ads09-f9a-0asd9f-ad asd9f0ae9f ad9f-as0df9ia-sd
-various signs and soforth- scrolling by same as the zodiac, on a larger scale?
i--^--i --arms
i-0-i -solar's position between the arms
o -centerpoint of spiral arm galaxy.

^ would be the view out from sol to the void between galaxies
==?== would be the gap and ?sign that passes current vision
Kinda makes sense in a creepy "how do I understand that" fasion, anyone agree? disagree? supporting evidence? demolishing evidence? any input in any regard will allow me to develope further this line of inquery.

26-04-2010, 09:17
You can find free Astrological software at:


I've not got personal knowledge of all of these so any you download aare in a real sense up to you. I have used three off the Western Astrology list - Morinus, Riayl3 and John Halloran's Astrology for Windows. The latter is a very good general purpose program for beginners, though to get the best out of it, you have to register it. So if you're not prepared to pay anything then the other two are all that I can mention. It's possible to add the Swiss Ephemeris to Morinus (instructions on their website) but for your use the built in ephemeris should be fine. Neither of these programs gives you anything in terms of built in interpretations (which to my mind is actually a bonus) and both assume that you know what you are doing with Astrology - so you will also need some books as well. If all you're looking for is something that will calculate planetary positions for any time on any day of any year, then all three will do that for you and you can ignore the other information.

I don't really know anything about the Mayan civilisation which would allow me to answer your question. Western Astrology is divided on the issue of other rotations. The majority use the 'Tropical Zodiac' based on the equinoxes and solstices and which doesn't really take any other movement into consideration (in terms of movement beyond the zodiac). The minority loosely follow the Indian and early Greek approach of using the Sidereal Zodiac, that is measured in terms of a star or other marker in the constellation of Aries. You will find other threads on that matter, so I'm not going into it in any detail, other than to say that my above statement on the Western Siderealists is OK as a basic statement of difference but by no means a fully accurate picture of their agreements and disagreements with Vedic and Greekk practices.

If you follow a Sidereal view then you have to recognise that the equinoctial position moves backwards through the zodiac at a rate of approximately 1 degree every 72 years. I'll leave it to you to work out how long it will take for the equinox to move entirely round the sidereal zodiac and return to 0 degree Aries (where it was som 1,800 years ago). This movement though is not the same as the rotation of the spiral arm, which I think is somewhere around 200 million years (though I stand to be corrected on that). Worse still the Sun is moving inside the Milky Way galaxy relative to other stars - it's moving in the direction of the constellation of Hercules.

For day to day Astrology these other movements are not really relevant at all. Over a century or so, precession might well be taken into account and you will find posts on this forum by Dadsnook2000 on the advantages of correcting for precession when making predictions for older people.

26-04-2010, 09:26
again, you enlighten me, I like the native american insight, as they are the original people from this continent and I carry some of their genes, I'll probably begin following their tradition, as it probably isn't as influenced by the eastern traditions we brought over. Thanks for the link, I'll find one to suit my purpose, the precession stuff is like, chinese to me, but, clearly it defines one point though, like our current calender and time system, the method for calculating the movement of the heavens is fatally flawed, its like no matter how hard we try math just doesen't seem to apply to the workings of our world.. only the parts we've 'created' ourselves.