And Ketu.

Similar questions arise for Ketu too. Ketu is the other NODE of moon, the point on Ecliptic where moon crosses it from north to south. It will not be diametrically opposite to previous Rahu position but a little away. ketu is also only a position and at Ketu there is nothing. Like rahu, ketu also moves backwards in successive moon orbits. It can hardly be described as motion of Ketu as it is not a continuous motion like planets but a series of spots.

As in case of Rahu, I wonder whether our ancient Astronomers had the same concept of Ketu as the current one. With visual observation, how can one decide where the moon crosses the Ecliptic? As Ketu is supposed to cause Lunar Eclipse, did they understand Ketu as Earth's shadow? It is known that Lunar Eclipse is caused by Moon passing through Earth's shadow (Umbra and Penumbra). How do the old astronomers describe the movement of Ketu and specify its position at any given time?

Moon will pass through Ketu in every orbit. Only if it happens to be a Full moon night, there will be a Lunar Eclipse. Even if Sun and Moon are not exactly 180 degrees apart but + - 6 degrees, a partial Lunar Eclipse is possible when mMoon is at Ketu. This is probably the explanation why Lunar Eclipses are more frequent compared to Solar Eclipses. For Solar Eclipse to occur, Sun must be at Rahu Node, (which itself does not happen frequently. Does it happen once in each Year?) and moon too must be at the same place on Ecliptic, not too much above or below.

I am interested in knowing what exactly our ancestors understood by Rahu and Ketu. I am not convinced that they understood them as Nodes of Moon on Ecliptic. I invite readers to share their information on these points.

What is Rahu?

Rahu, I understand, is the NODE or point of intersection between Sun’s and Moons paths, where moon crosses the Ecliptic from South to North. So it is just a SPOT. There is nothing at the spot! I further understand that the position of Rahu in each consecutive Lunar orbit changes slightly, moving retrograde along the Ecliptic. This is the so-called motion of Rahu. Does the change in position move equally in each Orbit on Moon? I dont know.

I further understand that the location of Rahu goes around the Ecliptic , moving retrograde and takes about 18.6 years for one orbit of its own. I take it that these are Solar years. They equal how many Lunar months? 18.6 x 12 = 223 plus Adhik masas at 1 per 29 months or plus about 8 or total 231 lunar months or thereabout. If Rahu moves at a uniform rate, then each time it moves about 360/231 or 1.5 degrees approximately. After going round the Ecliptic does Rahu come back to the exact spot it started from? I dont think so but would like to know.

I am not sure of these calculations and would like to hear about them from readers.

My main question is different. Did our ancestors have the same concept about Rahu?

It is difficult to believe that thousands of years back, when there were no telescopes, anyone could identify a NODE of moon, leave aside its changing position per orbit of moon! So what did they understand by Rahu? Their concept was it was something which caused Solar Eclipse. We know that Solar Eclipse is caused by the moon coming between Sun and Earth. So was the old concept of Rahu, ‘something’ directly behind the moon as seen from earth? How do the ancestors describe motion of Rahu? How do they designate ‘location’ of Rahu at various times of the day month or year? I invite readers to throw some light on this issue.