Parallax, Aberration, Planets in Houses  - fine structure of Ephemeris 

written by Sergey Tarassov


I often receive a question from users regarding the difference in time for different astronomical/astrological phenomena calculated by different programs or even by the same program. While all programs claim the highest accuracy of their calculations, the result of these calculations is so different. 

Look at this example: 



Here you see two tables showing the culminations of aspects for the slow planets. The calculations are made by the same program. The difference for Saturn-60-Pluto culmination is more than 10 hours in these tables. This discrepancy is very significant and can affect the performance of the models based on this phenomenon. However, you may say that slow planets are responsible for long terms trends mostly, so 10 hours do not make a big difference for your purposes.

Ok, I will show you another example:

Here the colored bars show the position of the Moon in each degree of Zodiac calculated by one and the same program. The discrepancy more than one hour for intraday data is more than important.


It looks like we have a problem here. The first thing that may come to your mind is that it might be a bug in the software. No, it is not. All these discrepancies are related to well known astronomical phenomena - aberration and parallax. The possibility to take these options into account are present (or should be present) in all astrological/astronomical programs. In Timing Solution you can find these parameters in "Options":




If we look at the Moon, what we really see is the Moon as it has been one second ago. Watching at the Sun, in reality we observe the Sun 8 minutes ago. Jupiter prefers to show his face with 40 minutes delay. The closest star, Alpha Centauri, appears to us with more than 4 years delay. The most distant object observed by space telescope Hubble (2006) is as far as 13 billion years of light traveling. According to modern knowledge, the size of our Universe is about 15,000,000,000 light years. This is how much the Universe has increased in size from the Big Bang time.

This difference of a displacement in the apparent position of a celestial object from its true position caused by the finite light speed is called aberration. For the Sun, the aberration is 8 minutes; during this period the Sun travels over the sky and covers 20 seconds of its arc. So, the discrepancy between the Sun's position with/without aberration is the difference between apparent and true position of the Sun.

Do we need using the aberration or not?

The answer to this question is based on another question: how do the planets affect us? Do they immediately affect us or their effect is delayed? 

According to the modern science, the speed of the light is the maximum speed possible in our Universe. According to Einstein's theory of relativity, we live in four dimensional time-space continuum where time and space are not separated (so called Minkowski space-time). We cannot tell where the Sun is located now, because "now" depends on our own position in the space. The Sun is separated from us not only by 1,495,000,000 kilometers, not only by 8 minutes of time; we are separated by a reason. In other words, time is related to reason, reasonality. To help you understand this idea, imagine that you speak over the phone to somebody who lives on the Moon. It will be a little bit awkward conversation as there will be 1second delay between all sounds. However, the difference is not too big, and in a few minutes you will adjust yourself and continue the live conversation. Now, if you would speak over the phone to another friend who is in the spacecraft flying around Jupiter, - the live conversation will be impossible due to 40 minutes delay. According to the modern science, it is impossible to change this situation in the nearest future - because the speed of the light is the maximum possible speed in Nature. The world of your friend on Jupiter and your world on the Earth are separated from each other by 40 minutes. This distance is unsurpassable as the distance between me now and when I was 15 years old kid.

This is nowadays point of view. However, we do not know what the science will discover in 25, or 50, or 100 years from now. 

What we have now is this: setting the aberration option OFF, we assume that some planet affects our earth life immediately, without any delays. We do not know it for sure. Setting this option ON, we assume that the affect of celestial bodies on our earth life is delayed. We do not know it for sure either. The experiments and research are the best way to understand what works better.


Imagine now two friends. One of them lives in New York, while the other lives in Moscow. Both are looking at the Moon at the same time and measure accurately the Moon's position. They will be surprised as the position of the Moon will be different. This difference can reach 1 degree in longitude. It is called "parallax".

If somebody sets the parallax option OFF, it means that he calculates the Moon position for a happy observer who works exactly from the center of the Earth. In real world, we observe the Moon and planets from the Earth's  surface, and the planetary positions depend on the place of observation (i.e., country/town).

The parallax can cause very interesting effect. As an example, the transiting Saturn can change the direction of its movement THREE TIMES DURING THE DAY. Can you imagine that?!

Let me explain how this is possible. Everybody knows that on  April 19, 2007 the transiting Saturn ends its retrograde motion and starts the direct one. If we look at graphical ephemeris, this fact looks like this:


But let us look at April, 19 trajectory closer. Here it is:

Is this a mistake? Why the Saturn's trajectory is so irregular? Everything works OK here! These irregularities are caused by the Earth's rotation. When Saturn is stationary, the Earth's rotation has so strong effect on Saturn trajectory. This diagram is calculated for Toronto, Canada. As you see, Saturn starts its direct motion early morning on April 19, then around noon it starts its retrograde motion once again, and at midnight it starts the final direct motion. If we observe the Saturn's motion from another place, we will get different moments for turning points. This effect is especially strong for countries located around the Equator, while it is lessen for countries with high latitude.

It is very interesting to study this effect for progressive planets. Pay attention to the moments when the progressive planets change their direction. This is a very seldom event, and these turning points are located within a year. It may give you a valuable information. All this work can be done with Star Trax Millennium software.

Planets in Houses

The houses were invented to point out the planetary position regarding the horizon. There are dozens of different house systems. However, you can imagine any house system as an orange that consists of 12 pieces. When the planets fall into one of these pieces, we say that the planets are located in some houses. But there is one very important issue here. The house ("the orange") that we analyze is a three-dimensional construction while the horoscopes we used to see are just projections of this three-dimensional construction to some plain (usually ecliptic). This makes this approach inaccurate. For example, Pluto located in the first house of the chart can fall into another house (let it be the second house) of the twelve-piece orange, due to Pluto's incline to the ecliptic. In other words, the location of the planet in particular orange piece is a bit different than its projection. This is why the moments when the planets rise do not correspond to the moment of the exact conjunction of this planet and the Ascendant.     

Minding all the above, we use the special zodiac, "In Mundo". To understand better how it works, consider the chart calculated for January 12, 1977 9:14 PM GMT Russia, Moscow.  



According to this chart,  Pluto is in the first house. Is it really in the first house? No!

Look at "In Mundo" chart:


This chart looks like a cosmogram, though instead of Zodiac signs there are houses there. Now you see that Pluto is located in the twelfth house now.  Here we use very accurate algorithms  developed by Russian physicist Dmitri Osipov. The conjunction with zero degree of Aries corresponds to the rising point, there is no discrepancy here.

So whenever you wish to analyze the exact moments of planetary ingresses into certain houses, better use In Mundo Zodiac. This is especially important if the analyzed planets have a big geo latitude. First of all it concerns Pluto, especially in the current period of 1950-2008 years (Pluto's latitude is more than 5 degrees North). Also high latitude is typical for Venus and Mars as well.

Practical recommendations

1) When you calculate the Moon (lunar) return or charts for Moon phases, the use/not use of parallax can change the results drastically. The parallax for the Moon may reach 1 degree; it corresponds to 2 hours, and the Ascendant can go through the whole sign during this period. Besides the results strongly depend on the place where you observe this phenomenon, so take care while defining the location. Try both variants, with/without parallax, - and let us know about your results.

2) When you calculate the Solar return chart, the usage or not usage of aberration may lead to 8 minutes of time difference. It is enough to shift the house cusps for Solar return up to 2 degrees. Therefore, take a good care while defining cusp positions and positions of the planets in the houses. To analyze the planets in houses, better use In Mundo Zodiac. Try both variants, with/without aberration, and let us know about your results.

For Star Trax Millennium (v.6) users: To calculate Solar or Lunar (Moon) Return and other cycle charts, use "Techniques"->"Cycle Charts". You can display In Mundo chart right here:

Also check other available types of cycle charts:

With our program, you can calculate practically any possible cycle chart: Solar or Moon return, Moon phase return, Ingress of the Sun (or the Moon) to Zodiac signs or Houses, etc. For some types of the charts the choice of Tropical or Sidereal zodiac may be crucial. You can do the choice here:

The "Phase between planets" chart allows to find the moments when the angle between two transiting planets reaches exactly the same angle as it is in Natal chart. Try to set these options:

You will look for the exact moments when the transiting angle between Venus and Jupiter repeats the same angle in the Natal chart.

You can calculate the return of any planet. For example, to calculate Jupiter returns set these options:

You can immediately see all your Jupiter returns charts. The "Returns" table shows the repeating astrological phenomena. In this example, you see that both charts, natal and Jupiter return's, have Venus in the second house, Mars in the tenth house, the Sun aspecting the North Node and the aspect between Neptune and Pluto. This may give you some hints regarding upcoming returns.

Sergey Tarassov.

Toronto, Ontario

February 22, 2007

January 27, 2011