Parallax and topocentric positions

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Namaste Anantarupa,

 

> Namaste Narasimha,

>

>

> Many thanks for pointing out that topocentric vs geocentric

> controversy is different from parallax.

> Would you mind to say a few more words about this

> parallax error as I dont really know what it is?

>

>

> Regards, Anantarupa

 

I am cc'ing this to vedic astrology list too.

 

Q: What is Parallax?

 

A: Take a glass that is half full of water. Put a pen in it in such

way that half the pen in inside water and half outside. If you

practically try this, it will seem as though the pen has bent at the

surface of the water. Between the portion of pen under water and the

portion above it, there will be an angle!

 

When light rays starting from a point under the water reach the water

surface while reaching us, they are " refracted " by an angle depending

on the densities of the two media (water and air) on the two sides of

the surface. When light leaves one medium and enters another, it

bends. This refraction is the reason for pen appearing bent.

 

Q: How do some people use it in Astrology?

 

A: Astronomy only tells us the " true " positions of planets. The

position where it " appears " to us will be slightly different, because

light from it is refracted when it enters atmosphere (vacuum and

different layers of atmosphere have different refractive indices).

This is just like the pen under water in the previous example.

 

Some people *speculate* that Indian sages did not use the *true*

positions of planets and they only used the positions where the

planets appeared to be (because that is what they could measure).

 

So they create the apparent positions from the true positions given by

astronomy by bringing in parallax. They use those positions in casting

charts.

 

Q: Are these calculations accurate?

 

A: No. Parallax can never be calculated correctly. It depends on the

temperature and pressure profile of the atmosphere above a place,

which changes considerably from time to time. Based on these changes,

the refractive index profile changes and the overall angle changes.

What most software programs give is only an approximation.

 

Q: Should we use parallax? Should we use true positions or apparent

positions?

 

A: I don't buy the parallax thing for two reasons:

 

(1) It is questionable to think that maharshis who knew the

fascinatingly deep subject of Vedic astrology did not know about

parallax to correct for it. Did they use wrong data, do statistical

research and come up with all this brilliant stuff? Probably not.

Parasara claims that he learnt these things from Brahma and Shiva.

 

(2) Parallax is defined only when a planet is visible. If we should

prefer the location where a planet *appears to be*, then what do we do

when a planet is not visible??? After all, planets are not visible

half the time! When a planet is not visible, what should its longitude

be?

 

Reason (1) is subjective and based on belief. But reason (2) should

knock down parallax. Obviously, we must use the true astronomical

positions of planets and not the positions where they appear to be.

 

Q: What are topocentric positions?

 

A: If we take the center of earth as the reference point and measure

the planetary positions from there, we get geocentric positions.

Topocentric positions are the positions with the reference point taken

at the birthplace (instead of the center of earth). This makes a few

seconds of difference for other planets and something of the order of

1 degree for Moon.

 

Q: Should we take geocentric positions or topocentric positions?

 

A: It is a tough question and we can argue either way.

 

Q: What do you use?

 

A: I (Narasimha Rao) use geocentric true positions, but I keep my mind

open. I will give the users of " Jagannatha Hora " software an ability

to experiment with everything (true vs apparent, geo vs topo).

 

May Jupiter's light shine on us,

Narasimha