Take a Horizontal line,the top of your monitor, edge of a window or the horizon itself. close one eye and bring one finger in front of your face in a way that it crosses the horizontal line. close the open eye and open the other one without moving your finger. you will notice that your fingers position changes relative to the horizontal line. Each eye sees a different position of the horizontal line crossed by your finger.
we have the same phenomenon with the crossing point of moons orbit and the ecliptic. Moons orbit is very close to our eyes compared to the ecliptic (which is the suns orbit).
I don't know how exactly the Rishis wanted us to calculate the position of Rahu/Ketu but as @ernst explains astrology's roots are in observation of the astronomical events. So if we take Rahu/Ketu as an astronomical observable phenomena then this must be also true for them.
when we are considering an observable astronomical event such as an eclipse then finding Moons orbit junction with the ecliptic from the observer point of view becomes very important.
I was wondering if Kala is using Swiss ephemeris which is derived from NASA JPL ephemeris then how come Kala shows an eclipse could have happened at July 14th 1787 while NASA doesn't have it in it's data base.
I believe that for this particular date, the deference from the observer position has cause the confusion, and there was no solar eclipse on July 14th 1787.
I calculated the approximate maximum difference in the angle of view of 2 observers at opposite sides of earth one seeing the moon rise and the other the moon set at the same moment. It is:
1 54' 52'
Meaning if one is seeing the moon at 0 Aries, the other will sea it at +/- 1 54' 52 compared to the first.
Yes, the visual of an ecplise depends on the location of observer, as does combustion and planetary war. However, planets for purposes of sign position are calculated to the center of the earth as the ecpliptic is based on the center of earth. House positions in a bhava chalita chart, SHOULD BE, calculated based on observer, but they usually are not, they are in kala though. So if we use observer or center of earth depends on the plane of reference we are examining.
Thank @ernst
What about Rahu/Ketu, Are they considered planets and Calculated from center of the Earth ?
If yes, for calculating the Start and end of Solar Saros cycles when eclipses are partial and very mild and only observable at north or south pole we may not have enough information to find out if they are happening.
For example when Sun/Moon conjunction is about 17 degrees from Rahu/Ketu then the moons orbital plane inclination to ecliptic plane (measured by Latitude) and moons distance to earth may start playing a role for the eclipse to occur.
I'll give details on the eclipses given by Nasa and Eagle and the lark in an other thread.