What do you think of when you hear or read the term ‘celestial mechanics?’ Some guy in greasy overalls giving Halley’s Comet a lube job? Replacing the Sun’s spark plugs? Let’s hope not! It’s a much more grand and complicated subject.
The Principia of 1687 was the beginning of modern analytic celestial mechanics. It is a 3-volume set of books by Isaac Newton on his laws of motion and of universal gravitation. The book brought to light the laws of planetary motion first expounded by Johannes Kepler in 1609. Kepler claimed to be able to track the orbits of all the known planets, so that astronomers would know where to look for, say, Venus, on any given night. But his mathematical proofs were not detailed enough, and his planetary tables languished in obscurity until Newton was able to show with his advanced calculations (otherwise known as calculus) that yes indeed all the planets in our solar system had a set orbit that never varied. You could set your watch by them.
More recently, the term “celestial mechanics” came into use as a way to differentiate it from ‘classical mechanics,’ which dealt with the movements of machine gears and projectiles. In other words, you would use classical mechanics to build a rocket ship to travel to Neptune, and then use celestial mechanics to figure out exactly where to point your rocket to score a bullseye.
The discipline should be dubbed “rational mechanics,” according to Isaac Newton.
Gottfried Leibniz coined the word “dynamics,” while Pierre-Simon Laplace coined the phrase “celestial mechanics” more than a century after Newton.
There was little relationship prior to Kepler between accurate, quantitative predictions of planetary locations using geometrical or arithmetical approaches and contemporaneous debates of the physical reasons of the planets’ motion. What that means in plain English is that before Kepler claimed to be able to track and predict the motions of celestial bodies, the motions of the planets was ascribed to all sorts of fanciful things – like angel armies wafting from one battle against Satan to another, or invisible shooting stars ramming planets at odd hours of the day and night to make them go faster or slower.
Which brings us now to the French mathematician and astronomer Urbain Le Verrier, who lived in France from 1811 to 1877. During much of his lifetime the extent of the solar system was thought to consist of the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Uranus. And Uranus wasn’t discovered by telescope until 1781 by William Herschel.
But astronomers suspected there might be more planets way out past Uranus, so far from the Sun that they would not reflect enough light to be seen by regular telescopes. And they were right. But it took a mathematical genius like Urbain Le Verrier to prove it with celestial mechanics backed up by mathematical calculations.
What tipped Verrier off that there might be something out there past Uranus was the observation that Uranus did not exactly follow the orbit it should have, had it been completely obedient to Newton’s law of gravity. After months of painstaking observation (and you’ll notice throughout the history of science that nobody ever observes something leisurely, but always painstakingly and/or thoroughly!) the French astronomer began to compose a series of complex mathematical equations to explain Uranus’ unruly straying from its dutiful orbit around the Sun. In 1846 the French astronomer mailed the fruits of his feverish mathematical conjuring to Herr Johann Galle of the Berlin Observatory. Galle pointed the mighty Berlin Fraunhofer refractor telescope where Le Verrier told him the new planet would be, and there it was!
Since then astronomers have been studying this distant ice giant intensely, slowly making it give up its frozen secrets. The orbit of Neptune, as you can imagine, with it being over 30 astronomical units away from the Sun, is pretty long. Neptune completes one complete cycle around the Sun every 165 years. So each of the four seasons on that remote planet lasts nearly forty years. A forty-year summer sounds rather nice – but the opposite side of the coin is that winter would also drag out to forty years!
The core of Neptune is a freezing mass of watery slush and silica rocks. Surrounding this core is a seething globe of water and liquid methane, with a touch of ammonia. Above the globe swirl massive clouds of hydrogen and helium. With just a hint of methane to make the planet appear to astronomers to be a deep rich blue.
Winds on the planet, according to radio telescope readings, can reach up to twelve-hundred miles per hour. Which means they break the sound barrier to create what some scientists call a continuous deafening thunder.
Neptune has rings, just like Saturn, composed of rocks and ice crystals. It also boasts 14 moons, and may possess many more that we can’t track just yet.
The largest moon is named Triton, and appears to harbor an underground aquifer that could actually be a full-bodied ocean in disguise.
Neptune’s secrets and mysteries continue to be well guarded by distance and an extremely active environment. Only one satellite, Voyager 2, has gotten close enough to snap a few photos back in 1989.
Neptune is classified by astronomers today as an ‘orphan’ planet, because while there is general interest in it there is no specific intent by NASA or other space agencies to spend much time or money on further research of that cold blue ball way out there. Mars and the Moon are the hot ticket items among the public and the scientists nowadays.
It doesn’t look like Neptune is going viral anytime soon . . .