let’s list down some facts:
- Earth revolves around Sun.
- Moon revolves around Earth.
- If all three align in a straight line, then (guess what?) eclipse happens. (If Moon is in the middle, then, Solar eclipse and If Earth is in the middle, then, Lunar eclipse.)
“Oh, Come on Buddy, we all know these, please don’t repeat basics”
Okay, alright but I’m gonna repeat them again but with extra details.
- Earth is tilted 23.5 degrees around its rotation axis, and it revolves around Sun; That is why, we have seasons.
- So, as an observer on Earth, we see Sun does not rise in the exact East ALWAYS.
- Moon revolves around Earth.
- Based on the above observations, imagine a trajectory of Sun and Moon around Earth. Both the trajectories are not Co-planar.
Now, observe closely, there are two points (nodes) of intersection of the trajectories in the Earth’s sky map. Eclipses happen only when both Sun and Moon enter those two particular nodes at the same time.
If both Sun and Moon are in same node, then Solar eclipse and if Sun in one node and Moon in other node then Lunar Eclipse. Since, Sun’s and Moon’s trajectories around Earth are not co-planar and have an angle of 5 degrees (as can see in the above picture), Eclipses don’t happen on every full moon day and new moon day.
Now, do you know what those 2 particular nodes are called generally (In India)?
HINT:
Did the picture ring the bell?
Okay, let me tell you. That is the picture of Rahu and Ketu. They both swallow Sun and Moon occasionally causing Eclipses.
Rahu being North Lunar Node and Ketu being South Lunar Node.
Before we getting the knowledge of Earth’s 23.5-degree tilt on its rotation axis, our ancestors knew it all and gave them fancy names as well.
Bonus: Have you observed that Sun rises in the exact east in the month of March and according to Hindu calendar, new year is celebrated in the same month known as Ugadi (in Karnataka). In other states, this festival may be known with other names. Uga + Adi which means start of the year.