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Rahu/Ketu and Eclipses

By Kshitij Sharma, August 12, 2005

When scientists announced discovery of a planet beyond Pluto, Times of India ran an editorial describing this as a failure of modern Astrology and it not being able to keep up with changing times.

I am of an opinion that this was totally unwarranted, especially in relation with Indian Astrology. Indian Astrology was concieved and developed when none of the outer planets, i.e. Uranus, Neptune and Pluto were discovered. It has withstood the tests of times and has been working well, if the ability of the astrologer in question is not suspect. Western Astrology did try to change its workings and did associate some qualities with these planets, but Indian astrologers stuck with the list of old planets. The new research, if it happens, is also based on the knowledge that is passed on from the old sages.

The Times of India article also ridiculed the practise of associating certain qualities with Rahu and Ketu as they are not real planets but are shadowy. They exist as mathematical entities and are given importance because they are instrumental in calculating eclipses, both Solar and Lunar. It is noteworthy that in Indian mythology, Rahu and Ketu were the demons that tormented Sun and Moon and caused eclipses. Astrologically both Rahu and Ketu tend to drain energy out of all planets, especially Sun and Moon.

You need to understand that as an observer on Earth, calculations done in Astronomy tend to be geocentric and not heliocentric. I know that this is kind of  Greek and Latin :-) but in layperson’s language it means that although all planets revolve around Sun (heliocentric), to know the position in sky and to view them, we need to make calculations with respect to our position, which becomes geocentric. Anyway, consider the plane of orbit Sun around Earth (ok, you have been taught the other way in school, but remember, we are working in a geocentric system of coordinates). We give this plane a special name – the Ecliptic.

In the figure above, the ecliptic is denoted by the black dashed circle with Earth at the centre. The plane of orbit of the Moon is at an angle to this ecliptic. The line at which these two planes intersect is the nodal axis, Rahu at one end and Ketu at the other end. Solar eclipse occurs on a new moon day when Moon comes between Sun and Earth. For an observer on Earth, they appear at the same point in space. Lunar eclipse occurs when Earth comes between Sun and Moon, on a full moon day, i.e. all three heavenly bodies are in the same plane, with Sun and Moon being diametrically opposite each other. Mathematically speaking, during Solar eclipse, the angular distance between Sun and Moon is almost zero degrees and during Lunar eclipse, this angular distance is almost 180 degrees. The angular distance between these two can be zero and a hundred and eighty on other days, but on the day of eclipse, both of them are on Ecliptic as well.

If you want to consult an ephemeris (i.e. the chart that displays degrees of all planetary bodies) to predict an eclipse, you should remember that an eclipse occurs when Sun and Moon are conjunct and coincide with either Rahu or Ketu. Conjunction with Rahu and Ketu is important because all three bodies need to be in the same plane. Conjunction means that the degree associated with the planets is almost same. I keep saying almost because both Sun and Moon are not point objects. Even if they come close inasmuch as one disk brushing the other, an eclipse is caused. Now do you see the importance of these two shadowy planets?

The table below gives an example of the longitudes of Sun and Moon and that of Rahu and Ketu for some eclipses.

Update: August 23rd. Now that Pluto has been demoted to a category of dwarf planet, what happens to the Time of India editorial?

Date Eclipse Type Sun’s Longitude Moon’s Longitude Associated Node Comments
Oct 24, 1995 Solar Eclipse 186.5 186.4 Rahu (182.82) Sun and Moon almost coinciding and conjunct with Rahu
Sept 27, 1996 Lunar eclipse 161.03 348.16 Ketu (344.3) Difference between Sun and Moon = 187 degrees. Rahu/Ketu also conjunct
Feb 26, 1998 Solar Eclipse 313.54 306.1 Rahu (316.5) Sun and Moon almost coinciding and conjunct with Rahu
Oct 28, 2004 Lunar Eclipse 191.18 11.8 Ketu (188.3) Difference between Sun and Moon = 180 degrees. Rahu/Ketu also conjunct



5 comments

  • Comment by Anonymous on July 23, 2006 at 11:14 pm

    HOw about the Mission Impact, in which one comet’s path was diverted using nuclear explosion? That should also affect the balance of the universe?

  • Comment by S. Anand on September 29, 2006 at 10:04 am

    The problem lies with the English language as it doesn’t have a good enough word to describe a “graha”. When you say “planet” people associate it with the 9 planets (or 8 if you’d like) and then ask how the sun, moon, rahu and ketu are planets.

    I also don’t believe that the Hindus of yore didn’t know about trans-Saturnine planets. All the profound calculations they did were done without the help of telescopes and calculators, and I am sure they did answer the question “What’s beyond Saturn?”.

    The sidereal period of Uranus (85 years), Neptune (165 years) and Pluto (246.6 years) are way beyond a normal human’s life span and hence it would have been difficult to measure their effects on terrestrial occurences. Observations would have to occur for centuries before you could exactly say what Uranus, Neptune and Pluto did/ influenced.

  • Comment by Nawal on July 6, 2007 at 12:49 pm

    I am not sure about the Kalsarp Yoga. However, I have prepared my mind to go-ahead with due respect and regard as a form of GOD, even then I would like someone to please through-some light on this YOGA, considering the name, DoB and PoB are Ekta Trikha, 5.1.1978, New Delhi. Regards,

  • Comment by ashish sapre on May 5, 2010 at 11:24 am

    excellent article and nice explanation. Only one suggestion. you repeatedly mentioned that eclipse occur when earth, moon and sun are in the same plane. I think three bodies/points are always on the same plane. In my opinion “plane” should be replaced by “line”. all the three bodies can be on ecliptic and still there may not be any eclipse. Hence the three need to be collinear in order to make eclipse possible.

  • Comment by SHRIRAM S.BARVE on December 26, 2013 at 12:10 am

    I think,original cosmic-rays or flux may not undergo any change while going through the points of Rahu & ketu.
    There maynot exist any atmosphere like Moon.
    Do you agree?

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