Solar Eclipse – A Triangular Hide n Seek between Sun, Earth & Moon

“It starts with light, and ends with light, and in between there is darkness.”

Aryabhata, the ancient Indian astronomer and mathematician was the first to describe how eclipses occur and provided the first mathematical procedures to calculate eclipse dates in his book Aryabhatiyam.

His computational paradigm was so accurate that 18th century scientist Guillaume Le Gentil, during a visit to Pondicherry, India, found the Indian computations of the duration of the lunar eclipse of 30 August 1765 to be short by 41 seconds, whereas his charts (by Tobias Mayer, 1752) were long by 68 seconds.
Source – Ansari, S.M.R. (March 1977). “Aryabhata I, His Life and His Contributions”

The Triangle

An interesting plot of a popular Kannada (Indian) movie America America has a triangular love story between characters who are named after Sun, Earth and Moon. Earth is the female character, while Sun & Moon are male characters. The plot is based on the fact that, Moon might come between Sun and Earth, but Sun will never come in between Moon and Earth.

Astronomers and Astrologers like it equally

When the moon acts like a slow shutter in the celestial camera, and when the shutter closes completely the beautiful celestial photograph of a night sky with Sun and its Corona becomes visible.

Well, so the day on which moon comes directly in line between Sun and Earth blocking the Sun’s disc as viewed from Earth, is the day which all astrologers, astronomers and the public in general look out for. The astronomers and solar eclipse chasers in particular flock to those places where the total solar eclipse could be viewed. The astrologers are all out to make predictions both good and bad. Both, the astronomers and astrologers give warnings to the general public about what to do and what not to do during the eclipse period.

Confused Birds and Animals

Then we have the birds and animals who get confused during the total solar eclipse thinking that the day has ended and so start returning home only to get even more confused after the eclipse ends.

Apparent Size of Solar disc and Lunar disc make it possible

Now, the possibility of a total solar eclipse itself, isnt it an amazing fact? Just think about this fact which we take for granted. For a total solar eclipse to be visible on earth, in the first place, the size of the Moon as seen from earth (the apparent size of the moon) should be equal to or greater than the size of the Sun as seen from earth (the apparent size of the sun). Because if the disc of the moon as seen from earth is smaller than the disc of the Sun as seen from earth then we will never have a total solar eclipse at all!

The divine view of Solar Corona and the celestial Diamond Ring

Now what’s even more rare is the possibility of viewing corona, the sun’s outer atmosphere which otherwise is not visible from earth. For the famous Diamond Ring to be visible, the size of Moon as seen from Earth should neither be greater than nor smaller than the size of the Sun but should be almost the same as the Disc of the Sun, so that when the Moon completely obscures Sun, it exactly fits on to the disc of Sun so that the outer layers of solar atmosphere are visible to us. This would also cause the diamond ring effect immediately before and after the totality of the solar eclipse.

On a geological time scale we are fortunate enough beings to live in a time period where total solar eclipses is visible from Earth. Millions of years ago moon was much larger as seen from Earth and 600 million years later Moon will be much farther and hence Smaller and so will be unable to cause a total solar eclipse on Earth. Oh yes, moon is moving away from Earth by about an inch every year!

Moon’s Elliptical orbit – Total and Annular Solar Eclipses

The orbit of Earth around the sun is elliptic ie the orbit is an ellipse. So we have times when Moon is nearest to the Earth and times when Moon is farthest from the Earth. A total solar eclipse is possible only when the moon is nearest to the Earth so that the lunar disc is large enough to cover the entire solar disc. What happens when the moon is farthest from Earth and comes inline with Sun and Earth is an annular solar eclipse where in the lunar disc will be inside the solar disc causing the sun to appear as a bright ring around the Moon.

Note that the elliptical orbit of Earth around Sun also causes the size of solar disc as appeared from Earth to vary, but this is a relatively small variation due to the large distance between Sun from Earth.

Only on New Moon Days Please and why not every New Moon Day ?

Since it requires that the moon come directly in between earth and sun, a solar eclipse can occur only on new moon days. But, why can’t it appear during every new moon? Well, it would have been great to have a solar eclipse every new moon had the Moon’s orbit around Earth and Earth’s orbit around Sun been on the same plane. But unfortunately the orbit of Moon around Earth is tilted at an angle of 5 degrees with respect to the orbit of earth around Sun, and so only on those new moon days where both the orbits meet is it possible to have a solar eclipse.

Now since we have atleast two points where two planes inclined at an angle to each other can meet, there will be atleast two solar eclipses somewhere on the planet every year.

Lunar Umbra says Not more than 7 Minutes 31 seconds

Moon is rotating around the earth means that shadow of the moon on earth (Lunar Umbra) also moves at the same relative speed. Taking into consideration the speed of rotation of earth and the speed with which the moon’s shadow moves, a solar eclipse can never last for longer than 7 minutes 31 seconds at the most. But lo, the total solar eclipse of 1973 June 30 was viewed for full 74 minutes! How?

Well, aboard a Concorde flight which flew at a speed of over Mach 2 (Twice the speed of Sound) over Africa – the solar eclipse was chased all along its path and the totality was observed aboard the flight continuously for over 74 minutes. Read the fascinating story IN FLIGHT by Los Alamos about this popular solar eclipse chase. Learn more about Eclipse Chasers here.

Solar Eclipse Paths in the Future

Here is a link to Map of the total Solar Eclipses visible in the near future and their geographical paths.

Solar Eclipse – Explanation via Animation

And finally here is a beautiful page which explains in detail the mechanism of different types of solar eclipses via neat animations.

Happy Eclipse Watching Today :)

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  • xyz

    go to hell

    • http://www.hitxp.com Gurudev

      OK

  • http://www.sureshc.com Suresh

    Thanks for the clarification.

  • http://www.sureshc.com Suresh

    In the animation at http://alienworlds.glam.ac.uk/solarEclipse.html, sun is shown towards North direction. I didn’t get that! Any idea on this?
    Thanks!

    • http://www.hitxp.com Gurudev

      Its mid afternoon and the sun is directly overhead, and hence the 2d mapping of 3D space makes it look like it is in North.

  • http://twopaise.blogspot.com/ Suresh

    Very informative. To answer Divya’s question, as I’ve heard, it seems the rays of Sun and Moon and other planets have effect on human body. During the eclispse, these rays will have negative effect on the body (and in turn on the health). So, it is advised to have empty stomach during eclipse. Again, I don’t have any concrete scientific findings/proofs for this theory (which I’m trying to search).

  • Shashwat

    Dear Gurudev,
    I read on a China site some time ago (I don’t remember which site exactly) in which a Chinese was writing a lot about India’s culture – he said that the Industrial Revolution in Britain occurred because the Britishers took the technology of textiles from India, when the English East India Company had subjugated Bengal. I haven’t been able to find books which speak on this subject, but I want to know about it. If you know, could you please tell me.
    Regards
     
     

  • Divya

    Hi Gurudev,

    Glad to see you back !! Why do people say one should not eat during solar eclipse? any scientific insight to this ?

    • http://www.hitxp.com Gurudev

      Hi Divya,
      The reason it is advised not to eat during eclipse is because Sun is associated with digestion in Indian astrology and hence the absence of Sun when it is supposed to be present is believed to be reason for this advise. Another possible reason might be that Sun is the destroyer of harmful microbes and absence of sunlight will cause microbe population to multiply, probably people used to go out and eat when eclipse occured and hence this advise was given.
      But I am not sure about the precise reason for this :(

  • Sachin Purohit

    Interesting. Are Rahu and Ketu, the two points where the two planes intersect? With whatever vague knowledge I have about astrology, Rahu and Ketu are always at the opposite ends in a Horoscope. Something that should also be a characteristic of planar intersection points I think. Also I think the math involved in predicting the lunar and solar eclipses, take the positions of Rahu and Ketu into consideration. I do know that Rahu and Ketu are not real celestial objects.

    A slightly off the track question for you. The only relevance to this topic being, the motion of the moon. We see only one face of the moon. We also know that moon rotates around its own axis and revolves around the earth. We are told in School geography that we see only one face of moon because the rotation rate and the revolution rate are so well timed that we see the same half of the moon every time. Orbits are not known to follow rational numbers. What could be governing this coincidence that there is not even a small fraction of a difference that would show up in the form of a slight difference in the position of the spots I see on the moon?

    • http://www.hitxp.com Gurudev

      Rahu and Ketu are nothing but the ascending and descending lunar nodes ie the two points where the moon’s path meets the sun’s path ie the two places where total solar eclipse is possible :)