Combust Retrograde Planets
In Vedic Astrology all astronomical observations are done considering the earth to be the reference point. This system of observation is called 'geocentric'. In any system of measurements, the reference point is considered stationary, though it may actually be moving.
When a planet is retrograde it is closer to the Earth than at any other time during its orbit. Mercury and Venus (planets inside the Earth's orbit) are closest when their celestial longitude is exactly the same as the Sun. The planets outside the Earth's orbit (Mars, Jupiter, Saturn) are closest when exactly opposite the Sun...see below diagram.
Image Source: http://www.utm.edu/staff/nlillega/phil120.htm
From this we can easily understand that the outer planets (Mars, Jupiter, Saturn) cannot be combust whilst in retrograde motion.
Effect of Combustion (for retrograde inner planets)
I was recently asked the following question; "Some astrologers are of the opinion that combustion of Venus is not severe when it is retrograde as it is in between Sun and Earth and it's rays to earth are not blocked. It appears that this view could be correct. What do you think?".
All I can say is; "How very fortunate we are to live in this modern age of technology and be able to view, with our own eyes, the recent (2012) transit of combust retrograde Venus"
(5th June northern hemisphere, 6th June southern hemisphere)
See the below video from NASA and consider carefully what you see!
As we know, apart from the luminaries (Sun and Moon), Venus is the brightest object in the sky. Known in all ancient cultures as both the evening and the morning star, it shines like the brightest of diamonds. We all know, however, that a diamond lacking clarity and brightness is to be avoided as it will not be beneficial.
As evidenced in the video, combust Venus has no brightness whatsoever. What we see is a dark object crossing the Sun...confirming what the sages say; "If a planet is eclipsed by the Sun (combust) it proves impotent".
Yes, being closer to Earth during retrograde motion, Venus has gained a certain strength. This strength, however, should be judged along with the state of combustion. Just as a diamond devoid of clarity and brightness has a strong (negative) effect when worn next to the skin, so too does (combust) Venus when closest to Earth.
This is simple logic...confirmed by the ancient Rishi's and evidenced by the recent transit, recorded for all to see with their own eyes.
For those experiencing the dasa or sub-dasa of Venus, some adverse results are likely, relative (of course) to Venus position in horoscope.