Re: Benefic vs Malefic Planets

2
Those requiring explanation are the ones that are neutral/ambiguous in Greek astrology (the luminaries and Mercury) and the nodes. Indian systems of thought/knowledge often aren't very happy with things being ambiguous; they are very fond of classification.

In Indian culture generally, the sun is associated, quite naturally, with burning heat (the same word is used in the sense of 'suffering') whereas the moon is associated with coolness and moisture, so I think that pair is fairly easy. The Indian eclipse demon is, well, a demon, so the role of the nodes is not so strange either. (Ketu originally referred to comets, but they were generally regarded as bad news too.)

Mercury, I suppose, is a benefic mostly in the sense of not being a malefic. Indian texts do point out that Mercury is changeable; they also sometimes say that the moon is benefic when waxing but not when waning. And some authors make a distinction between fierce (which includes the sun) and malefic (which doesn't).
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5
Yes, later Indian astrology sometimes includes these calculated points known as upagrahas ('sub-planets'). What is your question exactly?
What is Gulika and how do you calculate it?
For Upaketu, they say add 16 degrees 40 minutes to Chapa, which will give Ketu (UpaKetu). What is the relationship and/or difference between Upaketu, Chapa and Ketu?

Appreciate your feedback Martin,
Blessings!

6
It might be easiest to think of the upagrahas as broadly similar to lots, in the sense that they are secondary points mathematically derived from the planets, and also in that different authors pay more or less attention to them. They are all regarded as more or less malefic, as far as I recall, but I never used them myself even when my own practice was exclusively Indian (a long time ago). They seem to have been more popular in the south, especially in Kerala (home to many unique divinatory/astrological traditions). I'm sorry I can't give more detail. I know there is some brief discussion of these points in the Ranjan Publications edition/translation of the Bṛhatp??r??śarahor??(ś??stra).
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