Tuesday, August 07, 2007

Book Review - The Neptune File

Last spring I was given a copy of The Neptune File. It’s been quietly sitting on my shelf, but I finally picked it up a few weeks ago.

As anyone that’s familiar with the history of science should be able to tell you, it’s not the quiescent field of fact finding that it often appears to be. Rather, new discoveries can often cause contentious situations (although such situations are not necessarily indicative of discoveries).

I’ve written about one such situation before in which there was a large debate over the so called “spiral nebulae” and the subsequent realization that these were actually “island universes” or, as we call them today, galaxies.

Neptune File illustrates another situation of this sort: The discovery and aftermath of the discovery of Neptune.

The story as it is told here, starts with an even earlier discovery: that of Uranus by William Herschel in 1781. At that time, the big thing for astronomers to do was to determine precise orbits of known planets, comets, and other celestial bodies. Knowing where they should be allows one to determine their location on the Earth, so having precise coordinates was especially important to seafarers long before the invention of GPS satellites.

Before precise measurement techniques were available, rough orbits were good enough, but eventually, astronomers realized that the planets weren’t behaving as predicted by the simplistic models. What was needed was to add in the gravitational effects of the other planets (namely Jupiter and Saturn since they’re the most massive by far).

But even adding in these perturbations from the innermost gas giants couldn’t quite account for why Uranus’ orbit would slowly drift off from predictions. Many hypotheses were given to explain this, such as some sort of ether, differential gravity, or even comet impacts, but none of them stood up to any scrutiny.

It slowly became clear that the only possible explanation was that there was another planet yet to be discovered, that was exerting gravitational influences. But how to find it? Uranus’ discovery was somewhat serendipitous when Herschel stumbled upon it almost by accident. Hoping to find another that way, especially one that should be further away and thus move slower, be smaller, and fainter, seemed somewhat unlikely.

Undergraduate astronomer John Couch Adams realized that it should be possible to predict this planet’s position mathematically. Quietly, he began working out the location and sent his results to Britain’s chief astronomer, George Airy. But Airy dismissed the predictions, replying to Adams with an inquiry as to whether or not his hypothetical planet could also account for some other errors in Uranus’ orbit. Instead of replying immediately, Adams decided to work on refining his calculations.

In the meantime, French astronomer Urbain LeVerrier began his own calculations and published them in a series of papers. When Airy caught word that a second person had predicted a location for the hypothetical planet very close to that of Adams, he secretly directed the observatory at Cambridge, under the direction of James Challis, to begin a methodical search for it by scanning an area of the sky the two predicted, and looking for any objects that moved.

The problem with this is that this required determining the positions of a large number of stars repeatedly for long periods of time. Doing positions a single time for that large an area alone would take weeks, but having to do it repeatedly meant the search would take months.

While Airy conducted his search, LeVerrier worked to find someone to search for the planet. He finally convinced Johann Galle to conduct a search. Galle compared recent star charts with a high degree of accuracy to observations at the eyepiece. He would describe the positions of the stars to student Heinrich d’Arrest who would make sure the stars Galle saw were on the map. Any star that wasn’t would presumably be the moving planet.

On their first night of hunting, they discovered an object less than 1ยบ from LeVerrier’s predicted position that did not correspond with any known star. They had just beautifully confirmed the mathematical predictions made by LeVerrier and, unknowingly, Adams.

Since Adams’ work had not been published, LeVerrier was initially given all the credit. But Airy, eager to keep the French from getting all the credit, revealed that Adams had also predicted the new planet’s position quite accurately. Furthermore, the Cambridge search under Challis had actually observed the planet on several occasions. But since Challis had not compared his observations with one another yet, the English lost out on the chance to make the discovery first.

The result of this was an intense nationalistic rivalry in which each country accused the other of trying to steal credit. Eventually the dispute died down and the consensus was that Adams and LeVerrier should receive equal credit.

This introduced an entirely new era of attempting to look for planets through their gravitational influences. It led to the prediction of the infamous “planet X” due to problems with orbits of Uranus and Neptune. However this was eventually resolved to be due to inaccurate estimations of the mass of these planets. It was also thought for a time that there may be another planet between the Sun and Mercury due to some strange properties of the innermost planet’s orbit (which was resolved with the incorporation of relativistic motion). But despite the failed predictions of those two planets, the technique has been refined and similar ones are now used to detect planets around distant stars.

Overall, this book is quite an entertaining read. It’s a very quick read (took me 3 days) and has almost no technical jargon (the most technical bit is the use of arcseconds which are defined early in). I’d highly recommend this book to anyone interested in the field as a wonderful reminder of how amazingly well science can make predictions, even if the politics gets somewhat muddled.

6 comments:

The Ridger, FCD said...

I read that when it first came out and enjoyed it enormously.

William said...

Oddly enough, I just finished this book as well (thanks to interlibrary loan and the Lawrence, KS public library system), and found it to be a very quick and entertaining reminder of everything I'd forgotten from my History of Astronomy class a fifteen years ago. Standage is a good, solid writer, and his two previous books ("The Turk" and "The Victorian Internet") are also worth reading. Highly recommended.

Anonymous said...

I know this entry of yours is from almost a year ago, but I just saw it tonight for the 1st time, so I hope that gives me a pass to quote you in your blog on the Neptune Files: (and sorry I'm a "God" person... just wanted to give you fair warning)

"Before precise measurement techniques were available, rough orbits were good enough, but eventually, astronomers realized that the planets weren’t behaving as predicted by the simplistic models. What was needed was to add in the gravitational effects of the other planets (namely Jupiter and Saturn since they’re the most massive by far)."

I wanted to say that this passage reminded me instantly of the way we can measure whether God exists or not. At least for me, it would be a way I'd ask someone seeking to know if I really believe it or not to judge me. Since we cannot use a telescope to see God, or a scale to measure the weight of a human soul, we measure what we can: the lives of those who claim to know God. While this leaves the scale wanting in many ways when considering the failures of public figures 'who have gone before', there are many more who live quiet lives that tip those scales - these are the 'gravitational effects' of God on the lives of those who seek him.

This is not to say that considering the pure and un-fooled-around-with rudiments of the mechanics of planets and orbits is not inspirational in itself. I don't mean to say I need to add this commentary in order to enhance the beauty of planetary operations: beauty for beauty's sake, ars gratia artis... as Metro Goldwyn Mayer had on it's lion's crest: "Art for Art's Sake." Astronomy for astronomy's sake is noble and pure, a celebration of applied science for the utmost goal - discovery of truth. I love it. I'm not in school, but I do what I can in my spare time after work: watch The Universe on the History channel, read some books when I can, especially ones about the elements.... I dont know why but I've always loved rocks. I just love the earthy basic-ness of them and the ways the elements interact, surrounding us and sustaining life. It's something I can't not be fascinated by. So I'm going to be reading your blogs... along with others...and I'm sure you're not complimented by someone of no credentials such as myself taking an interest in your blogs, but I have never really been a blog-reader, and tonight after seeing (ugh) Expelled and Google led me to yours, I saw some common interests and got hooked. I kindof wish I could have studied science in college, but I was one of many sheep herded into college after high school and had no idea what I wanted to do. I kindof see myself as a sort of Ben Franklin, a life-long self-learner. My Grandfather never went past the 3rd grade, b/c in the 20's he was sent to an orphanage with his brothers and sisters because his dad died and his mother could not afford to feed them. He worked on farms until he was in his 30's when he took up welding... before there was appropriate equipment, and he ended up legally blind by his early fifties. But in one of the last visits I had with him, he was talking about some physics he had been learning about in his books on tape. So I guess in a way, determining to be a lifelong learner is also a tribute to him... and a sign of some of his dna in me. Thanks for letting me add to this string.

Anonymous said...

I know this entry of yours is from almost a year ago, but I just saw it tonight for the 1st time, so I hope that gives me a pass to quote you in your blog on the Neptune Files: (and sorry I'm a "God" person... just wanted to give you fair warning)

"Before precise measurement techniques were available, rough orbits were good enough, but eventually, astronomers realized that the planets weren’t behaving as predicted by the simplistic models. What was needed was to add in the gravitational effects of the other planets (namely Jupiter and Saturn since they’re the most massive by far)."

I wanted to say that this passage reminded me instantly of the way we can measure whether God exists or not. At least for me, it would be a way I'd ask someone seeking to know if I really believe it or not to judge me. Since we cannot use a telescope to see God, or a scale to measure the weight of a human soul, we measure what we can: the lives of those who claim to know God. While this leaves the scale wanting in many ways when considering the failures of public figures 'who have gone before', there are many more who live quiet lives that tip those scales - these are the 'gravitational effects' of God on the lives of those who seek him.

This is not to say that considering the pure and un-fooled-around-with rudiments of the mechanics of planets and orbits is not inspirational in itself. I don't mean to say I need to add this commentary in order to enhance the beauty of planetary operations: beauty for beauty's sake, ars gratia artis... as Metro Goldwyn Mayer had on it's lion's crest: "Art for Art's Sake." Astronomy for astronomy's sake is noble and pure, a celebration of applied science for the utmost goal - discovery of truth. I love it. I'm not in school, but I do what I can in my spare time after work: watch The Universe on the History channel, read some books when I can, especially ones about the elements.... I dont know why but I've always loved rocks. I just love the earthy basic-ness of them and the ways the elements interact, surrounding us and sustaining life. It's something I can't not be fascinated by. So I'm going to be reading your blogs... along with others...and I'm sure you're not complimented by someone of no credentials such as myself taking an interest in your blogs, but I have never really been a blog-reader, and tonight after seeing (ugh) Expelled and Google led me to yours, I saw some common interests and got hooked. I kindof wish I could have studied science in college, but I was one of many sheep herded into college after high school and had no idea what I wanted to do. I kindof see myself as a sort of Ben Franklin, a life-long self-learner. My Grandfather never went past the 3rd grade, b/c in the 20's he was sent to an orphanage with his brothers and sisters because his dad died and his mother could not afford to feed them. He worked on farms until he was in his 30's when he took up welding... before there was appropriate equipment, and he ended up legally blind by his early fifties. But in one of the last visits I had with him, he was talking about some physics he had been learning about in his books on tape. So I guess in a way, determining to be a lifelong learner is also a tribute to him... and a sign of some of his dna in me. Thanks for letting me add to this string.

The Ridger, FCD said...

I read that when it first came out and enjoyed it enormously.

William said...

Oddly enough, I just finished this book as well (thanks to interlibrary loan and the Lawrence, KS public library system), and found it to be a very quick and entertaining reminder of everything I'd forgotten from my History of Astronomy class a fifteen years ago. Standage is a good, solid writer, and his two previous books ("The Turk" and "The Victorian Internet") are also worth reading. Highly recommended.