Awe-Science of Planetary Eclipse

Authors Date Time to Read License
ArunIssac + Ganesh + Surendar 05 Sept 2017
31 Jan 2018
30 mins. cc-by-nc-sa

We all have experienced enjoying atleast one eclipse in our life time. It is also emotionally rewarding for some. Every culture seems to have some kind of interpretation to it. However, for those who dared to question the normative rules, such astronomical events happening within Earth's vicinity help wonder about the possible reasons behind it. Scientific explanation in Astronomy so far has provided with tremendous amount of information that help realize the beautiful complexity behind it. After getting to know it, i personally realized how fortunate humanity is in time, to experience such awesome natural events.

It has also helped researchers, eclipse chasers, artists, by revealing the astronomical facts which apparently not visible or detectable without eclipse. At first, in fact we are being flattered by the shadows of one rock on another. The fact seems simple. But theorizing and proving the exact mechanisms are really really difficult. It simply takes time. We need to observe painstakingly. Some desperate researcher has to keep their eye glued to the telescopes in order to get reliable data to compile the observation.

Rare double eclipse image - with both Earth & Moon between Sun & SDO
Credits : NASA SDO

Since eclipses are phenomena that occurs when one enoromous rock in space casts shadow on nearby shadow for a brief duration, we are more interested in occultations that happens between star - Sun, planet Earth & its natural satellite Moon. I am not going into much details as like a wikipedia article or any other research institute could offer. I consider this writing as my view and learning from my peers ArunIssac & Surender. Eventhough eclipse is a pretty event, it is ArunIssac who have actually discussed with me about writing a interactive application that might probably help people to look into about eclipse and learn it from there. This stumbled upon while we were searching for personally entycing projects and seems to be a perfect candidate. Eventhough i do not know much of programming, i have immediately accepted to contribute to it.


Introduce me something that involves Electromagnetics, some Math, some Math which i can understand; Geography, Maps, Space; Complexity; Networks then i will make sure i am interested in it. Like everybody, i have known very little about eclipse stuff from what we have been taught in our schools. That is all for me. For looooong time i never cared about it much, than experiencing it for a very few times till now. Being friends of some communities around often we get to meet at someones place to discuss and deliberate of how things are going personally and socially. It ranges from hot burning socio-political-economics to sex-literacy; from movies to hacking stuff.

In one of such meetings, we have leaned to do things that we are individually interested in first place before going to do something collectively as a step towards to make individual more confident before taking the collaboration to next step. So everyone in had their own interests and likes. As usual, i am learning stuff that related to interaction, maps, modeling, etc... One fine day ArunIssac called me and asked What If ? there is an application of some sort that provides a neat interactive experience to the upcoming eclipse event that was bound to happen in the upcoming months. That is all i needed to set the ship in sail. It involves communicating about eclipse to others using some interactive thing, and i do know it involves usage of maps and visualization of some sort. Hell ya ! i am going to contribute in one way or other.


Several astronomers constantly study, look & observe several occultation events happening by scoping several planets from different observatories and artificial satellites, there is still much can be learned from the solar and lunar eclipses that we are fascinated with so much. Since most celestial bodies are governed by same natural laws that govern our local planets, whatever one learns about it, will eventually help to learn further and be wise in space exploration.

Well, i do not want to repeat stuff that are already available in Wikipedia and other wise websites contributed by clever researchers, and institutions that specialize in planetary occultation stuff. This is going to be like my personal lab diary and notes, and crediting my peers all along happily for the help they have provided me to learn this thing than i would have done myself. This writing/notes will represent a redepiction of what i have learned. It might be useful for someother folk like me. Since the eclipse events are a seasonal occurances, we believe it is not a niche thing to attempt and realized that its usage might be season based. Furthermore, we have media and internet to propagate the event. If at all used by researchers, students, amateurs then we might call it as a worthy contribution.

Planets move in relation to each other, based on their mass-gravitational relatonship. We generally know what orbits are, but yet not many of us know how they actually rotate around one another, why do they rotate in specific ways. This involves interpretation from lot of laborious, accurate & historical observations. Then building up the model from these tabulated data using techniques of mathematical modeling that makes the data sense and provides a meaning for the hardwork contributed to study & experiment.

All models are wrong, but some models are useful.

george ep box - George EP Box

It is wise to note how much physical and intellectual labour has been contributed in pursuit of understanding how nature works at this scale. I must thank for making it clearer, simple and interesting by Fred Espenak, through is Eclipse Wise website. It helped me like a wiki to learn about eclipse stuff.

It turns out that understanding besselian elements - a mathematical model trying to describe the details of eclipse phenomenon, called as occultation. But this might require a clever understanding of line, plane & spherical geometry. Or, one can just imagine about balls/spheres, papers/surface, shadows/projections to get a intution of what the mathematics is trying to explain. To understand its explanation, some ideations such as ideal sphere, are assumed. Once a proper model to workout the problem is in hand, it can further be complicated with several other real world variables and verify its validity with experimentation.

I hope i have tried properly to redepict what i have understood so far. Let's see how it goes.

Bit of Spherical Geometry

sphere with axis
We shall have a simple sphere with reference axis
sphere with surface cut
A plane surface (a paper) slicing the sphere
result hemisphere
If slicing goes well, we now have a hemisphere

Ideal Shadow Casting (Occulting)

Now one shall consider the ideal hemisphere as the slice of occulted body like Earth, so that when a occulting body like Moon casts shadow on it, the observer can realize them as circles, as illustrated below. However, this is only our mathematical thinking that provides us mental space to imagine for such a ideal case. And here we can see how the projections are simply circles.

shadows without perspective
Shadow casted by occulting body on the fundamental plane

Adding some Reality to it

Having a simple distortionless, non-perspective shadow casted on the hemisphere of a ideal occulted body like Earth with the help of a fundamental plane provides a framework to imagine and stick with mathematical and informational simplicity. On the other hand, reality is really complicated, thus necessitating us to add back reality by adding one parameter by one parameter that are carefully studied with theoretical analysis and accurately enough experimental measurement and verfication. In other words, from the humble simple mathematical realm, it extends itself to be dynamic by adding variables such as:

Let's see how it might look at one instance of shadows casted on the surface of the occulted body, or a complete sphere without slicing it down. Now, the shadow casted upon the surface of sphere is not a simple circle, instead looks like a real perspective projection that changes shapes based on the place where the shadow is casted. This depends upon where & how far the light source is? where the occulting body within the field of view of the occulted body is ?

shadows with perspective
Shadow casted by occulting body on the Surface of Sphere/Occulted body

This seems more like what we experience in reality. Besselian elements helps us to describe the movement of shadow on the fundamental plane, which in turn needs to be reproject the shadow cone back to the surface to make it more pragmatic. The above described parameters/variables comes in the play here and helps us describe the dynamics of occultation caused by one body on another even before it tends to happen. As our observation and measurement instrument gets more and more accurate, more and more data shall be added to the model making it express more reality. At the same time, we will also end up finding limitation of the models description accuracy, as atleast one of the variables involved might end up creating more error in the possible outcome. Since this is a astronomical space-time event involving an observer, its range of description becomes naturally time bound.

with rotation axis
Shadows on the Sphere with rotation axis of planet Earth

Furthermore, there are are several other models that help express the data required for the besselian computation. These models can describe the shape of occulting and occulted body, their rotation and revolution dynamics, eccentricity, etc... which might add to the propagation of error.

We can see that the besselian model for predicting the shadow casting (occultation) phenomenon is not unique for earth-moon-sun astronomical positions. It is also useful to determine occultation for planets transiting sun, which we can observe through telescopes from ground or from space telescopes. Moreover, both Solar Eclipse and Lunar Eclipse helps learn about the planets involved, their orbital position dynamics, actual shadows and lot other specific details involved. Patterns extracted from the observed data using sub fields of mathematics, really enables us to imagine in several different perspectives. Then the models are further evaluated to determine their accuracy in calculating the data even before experimentally observing it, eventually reaching a predictive boundary limit for the applying the model.


Certainly, it is about designing a interactive computer application that uses Free Software libraries with the goal of communicating eclipse stuff, and would inherently provide a educative package along with it to know how things work behind the screen unlike the proprietary software applications that was shoved for students and budding researchers. Fuck capital business models in Science. Even if someone has already done something similar, i would like to do something for it.

It is very clear that i had to learn a lot of things that usually an Astronomer would have taken in a College. But it is reasonable and fun. So far, i would not have learned about it unless i get stumbled upon it. This seems to involve fairly a straight forward process:

What i would personally imagine to have is something like the following image. Content of the image is not boring and illustrates reality happened over a time period in that particular place. On seeing the image, many of us still wonder how could it have been between the provided timestamps, and that is where our imagination kicks in like in a comic the action sets itself in motion between the frames. So i personally hope a design offering such interaction would be useful for anybody who is engaging it, and will remain in their memory that comes back when they again hear about eclipse.

Solar eclipse with timestamp
cc-by-nc-sa Solar Eclipse illustrated with Timestamp Information (like a comic)

Moreover, not everyone can have the liberty or facility to enjoy such awesome natural event. Even when somebody has both, they just cannot do their from their own position. That is what it makes a natural gift. With the rise of Internet, Information sharing platforms, it is very much possible to live video stream the event for those who could not atleast come to those places where it is vieweable. But it must also carry the knowledge along with it. A live video stream may stream the natural effect, but what caused it, what are the reasons behind it still needs to be communicated to people who are interested in learning it. Learning can be seriously fun. We need to atleast try to attempt it. If Learning needs information and tools that convey the information they need to be Free. It must be flowable without any blockades.

Upon understanding its place of requirement, i immediately understood if i am imagining it, then definetely people better than me and who have good interest, experience and expertise would have done a good contribution to it. So my web search yielded the following results which i considered as neat, informative & interactive - based on its purpose and usage. This further helped me expand my bookmarked list of designers.


What we have done so faaaaaar ?

Me being not good at coding and only familiar with basic programming have no idea where to start with while starting this project. On the other hand, ArunIssac as far as i know, who is great at programming and coding at his computer language of interest does not like programming in javascript for few reasons. But people have made it so, that any application must be either be developed for android or else for the web browsers. So our plan is to first make some web application so that indirectly we can learn about the web development so that we can adapt to some of its goodies - although we hate centralization, obfuscation and minification to the core.

Gathering Required Resources :

Even before starting to design the prototype, we made ourselves little more aware about the theoretical, mathematical stuff that underpins the scientific explanation behind the solar and lunar occultation as viewed by an observer from Earth. We found the following resources are very much helpful :

Step 1: Drawing

So... for me visual thinking works ease and nicer than a procedural/algorithmic thinking. It makes me wonder how i would be playing with such a tool if one is provided. I would : play around all the optimal functions manifested through the widgets in the screen (that does not make me feel dumb); i would probe to see if it is playful and to what degree it is entertaining; does it make me feel smart and simple at the same time ? i would see why such a tool is built; i would see what logic & math works behind the tool; i would surely like to see whose labour is contributed to make such a useful tool; if all goes fine, i would spread share it to all my friends.

To start with i have seen some of the images offered by NASA eclipse shadow plotted on a static 3D globe. But it is all static. It is honest, informative, but could not interact to let the exploration flow. You know, if a thing craves itself for exploration, it must be flexible to the let users explore it. Moreover, with very rapid advancement in web based data visualization and story telling techniques, visual designers have done some neat work in visualizing the solar eclipse stuff. Obviously it has helped me visualize further why these designers have explored and presented the same data in such ways.

Mockups tried out for Visual Layout

Thus i find the following features are necessary to be provided to user:

  • Option to choose between 2D Map or 3D globe
  • Use calendar to select the recent event or any one within range
  • Use interaction in Map/Globe - based on existing mental models
  • Show numerical data to give a little bad ass touch
  • Dont overload with excess options

Step 2: Coding

I know one thing for sure, coding for fun stuff is hyper fun. But somebody got to code it. I do know that i am not good at coding or programming either. But contributing a little like how i would spend some sleepless nights in order to bring some css and js in making this website itself - trying to figure out how they work is addictive too. :)


  1. Besselian Elements
  2. JSEX
  3. JLEX
  4. NASA Goddard Space Flight Center
  5. Washington Post - Denise Lu
  6. Washington Post - 2017 Eclipse Graphics Story