Continuing the massive scope of the show, episode three tells the story
of how mankind abandoned the notion that the Heavens were instructions,
left to us by the Gods. Changing only the seasons, the stars and 
movement of the planets told us about when to harvest, when to hunt, 
when to migrate. Stories of the gods were painted on the night sky, as 
constellations, different from culture to culture. But every culture saw 
the universe as created and controlled by the gods, the view of a 
newborn baby in a basket.

In such a static universe, the apparition of comets were thus, 
understandably, seen as portents of doom, across cultures. As different
cultures saw different patterns in the stars, they also interpreted 
comets differently, thinking they caused hunger, smallpox, death of a 
leader, or calamity for the state. Pattern recognition is a two-edged sword.

But what are comets? The host, Neil deGrasse Tyson, takes us on a 
beautiful journey, to the Oort cloud, and explains what comets are, and
why they appeared to the ancient cultures, at infrequent intervals.

Why is this important? Tyson tells the story of Edmond Halley, whose 
friendship with Isaac Newton, and their strained relationship with 
Robert Hooke, curator of experiments at the Royal Society, and the 
discoverer of the cell, eventually resulted in the explanation of why 
the planets moved the way Kepler had shown, almost a century earlier.

Halley, himself a scientist, whose discoveries and scientific work has 
earned him a place among the greatest in science, believed there had to
be a mathematical law to describe how the force who keeps the planets in 
orbit around the sun. Hooke claimed to have the solution, but never 
delivered. Halley then turned to Newton, who feuded with Hooke over 
discoveries such as the mystery of the spectrum of light. Newton, whose
work on alchemy, biblical codes, and the Second Coming had taken him 
nowhere, told Halley the solution at once, that the attraction of 
gravity weakens with the square of the distance. Newton had done the 
math five years earlier, but couldn’t find his papers. He promised to 
send Halley the calculations, which he did. This in turn evolved into 
Newton’s masterpiece, the Philosophiæ Naturalis Principia Mathematica. 
However, the Royal Society had no money to publish it. Fearing it would
never be published at all, Halley agreed to do it, accepting payment in
the form of the book that had caused the pecuniary predicament, “History 
of Fishes”.

The value of “Principia” cannot be overestimated. With this work, we no
longer needed a master clock-maker to explain why the Heavens moved. 
Without the question-stopping concept of an intervening God, new 
questions could arise, and even be answered. One example was the 
discovery, by Halley, that the fixed stars were not at all fixed – they
moved, but this could only be observed, if they were tracked for centuries.

If planets and stars moved in ways that could be calculated and 
predicted by mathematics, wouldn’t this also apply to comets? Halley 
discovered that comets returned on a regular basis, by finding old 
accounts, and painstakingly calculating their paths: Comets were bound 
to the sun, just as planets were. This meant that the advent of comets 
were not portents of doom, of punishment sent to us by the gods, but 
could be predicted, with much greater accuracy than any of the mystics 
who had hitherto predicted anything. One such comet, returning each 76 
years, was named after him, Halley’s Comet.

This is one of the strongest characteristics of natural laws: They 
enable us not just to explain what happens in the present, but also to 
predict what happens in the future, as well as explain what happened in
the past. We can therefore say that, in several billion years from now,
our own Milky Way galaxy will merge with the Andromeda galaxy.

The baby in the basket is learning to walk, and to know the Cosmos.