H'ad Astra Historia - Ep. 305: You're So Predictable

0:00It's the 365 days of Astronomy PodGa. Coming in 3, 2, 1. I'm Loretta Cannon with the Historical Astronomy Division of the American Astronomical Society. And this is Hadastrath Historia, our official podcast. We're here to share stories from and about the people who study the stars, planets, and the cosmos. We'll be hearing from individuals who not only study the history of astronomy, but also

1:02those who lived it, who were in the room during pivotal events within the last 50 years or so. So please sit back and get comfortable for today's stories. Welcome to Hadastrath Historia Episode 305. Our theme today is the discovery of Neptune. This is a story of missed opportunities, undisclosed data, a bit of professional rivalry and a controversy that some still argue today. 180 years ago, on the night of September 23 to 24, 1846, which was the automno equinox

2:07that year, astronomer Johann Gottfried Gala, with assistance from Heinrich Darest, found the planet Neptune using the 9-inch frownhofer refracting telescope at the Burzlin Observatory. But that is not what makes this discovery so interesting. Gala was specifically looking for planet number 8 based on calculations sent to him by French astronomer Erbain L'Avériee. This was made because the known orbit of Uranus indicated that something was perturbing it. So basically, Neptune was identified or predicted first with mathematics using pen and paper and then confirmed with a visual observation. What a hoot, eh? Now, I get in things here and this would be the shortest podcast ever. But today's story is just a little bit more interesting.

3:11But first, let's start with some basics about Neptune. Though discovered in 1846, it would be another 140 years before we saw it up close and personal. On August 25, 1989 Voyager 2 made its 5-hour close flyby of Neptune and its largest moon triton. Though I should note, that Voyager spent 4 months observing Neptune both on approach and a bit afterwards while heading for interstellar space. Voyager 2 was the first and only spacecraft to visit our systems far this planet, a trip that took 12 years, with stops along the way to visit Jupiter, Saturn and Uranus. By the time it reached Neptune, it was traveling about 42,000 miles per hour, but still managed to acquire stunning and useful imagery and science.

4:14The ice giant Neptune is the only planet in our system that cannot be seen with the naked eye. It is so far out there that, when discovered, the existence of that planet almost doubled the size of the dead-known solar system. So listeners, there is this awesome short film, about 7 minutes, long from 2015, called To Scale, the solar system, in which these two guys and a couple friends built an accurate scale model of our solar system in a dry lake bed in Nevada. The sun was a balloon, about 1.5 meters in diameter. The earth was a blue marble, located 176 meters, or 579 feet away. The orbit of Uranus was 3.4 kilometers, or 2.1 miles, away from the sun.

5:15The orbit of Neptune was 5.6 kilometers, or 3.5 miles, away. I highly encourage you listeners to pause the podcast here, click the link in the transcript and watch this short film. It's such fun. Oh, and the other film worth watching for Info on Neptune is The Farthest Voyager, a full length documentary from 2017 that tells the story of the Voyagers, there were two. R2. Voyagers mission to the outer planets and beyond. The part about Neptune starts at 1 hour 13 minutes into the film. NASA's webpage for Neptune gives us a wealth of information, which I'll share some of that with you now. Earth, cold, and whipped by supersonic winds, ice giant Neptune is more than 30 times as far from the sun as Earth.

6:17In 2011, Neptune completed its first 165 year orbit since its discovery in 1846. It is an equatorial diameter of approximately 50,000 kilometers. Neptune is about 4 times wider than the Earth. Sometimes Neptune is even farther from the sun than dwarf planet Pluto. Pluto's highly eccentric oval shaped orbit brings it inside Neptune's orbit for a 20 year period, every 248 Earth years. This switch, in which Pluto is closer to the sun than Neptune, happened most recently from 1979 to 1999. Now Pluto can never crash into Neptune because for every three laps that Neptune takes around the sun, Pluto makes two.

7:17This repeating pattern prevents close approaches of the two bodies. Neptune's axis of rotation is tilted 28 degrees with respect to the plane of its orbit around the sun, which is similar to the axial tilts of Mars and Earth. But the main axis of Neptune's magnetic field is tipped over by about 47 degrees compared to the planet's rotation axis. Like Uranus, whose magnetic axis is tilted about 60 degrees from the axis of rotation, Neptune's magnetosphere undergoes oil variations during each rotation because of this misalignment. The magnetic field of Neptune is about 27 times more powerful than that of Earth. Neptune has 16 known moons. The largest Triton was discovered on October 10, 1846 by William Leselle, just 17 days

8:21after Gala discovered the planet through his telescope. Since Neptune was named for the Roman god of the sea, its moons are named for various lesser sea gods and nymphs in Greek mythology. Neptune is the only large moon in the solar system that circles its planet in a direction opposite to the planet's rotation. It's called a retrograde orbit, which suggests that it may ones have been an independent object that Neptune captured gravitationally. Triton is extremely cold, with surface temperatures around minus 391 degrees Fahrenheit, which is negative 235 Celsius. And yet, despite this deep freeze at Triton, Voyager 2 discovered geysers spewing icy material upward more than 5 miles.

9:22Triton's thin atmosphere, also first discovered by Voyager, has been detected from Earth several times since and is growing warmer. And scientists do not yet know why. Neptune has at least 5 main rings and 4 prominent ring arcs that we know of so far. It is one of two ice giants in the outer solar system, of course the other is Uranus. Most about 80% or more of the planet's mass is made up of a hot dense fluid of, quote unquote, icy materials, water, methane, and ammonia above a small rocky core. Of the giant planets, the outer four, Neptune is the most dense. Oh, scientists think there might be an ocean of super hot water under Neptune's cold clouds. It does not boil away because incredibly high pressure keeps it locked inside.

10:26And the planet does not have a solid surface. Neptune's atmospheres made up mostly of hydrogen and helium with just a little bit of methane. Uranus has a similar makeup. The methane absorbs other colors but reflects blue, giving these ice giants their similar hue. Many images of Neptune that came from Voyager 2's flyby in 1989 show Neptune as a much deeper blue. Now this was because the Voyager team tweaked the images to better reveal clouds and other distinctive features on the planet. Researchers in 2024 reprocessed the images, showing the planets, Neptune and Uranus, look much more alike than we have thought up till now. Neptune is our solar system's wu-ndiest world. Despite its great distance and low energy input from the Sun, Neptune's winds can be

11:31three times stronger than Jupiter's and nine times stronger than Earth's. These winds whip clouds of frozen methane across the planet at speeds of more than 1200 miles per hour or 2000 kilometers per hour. One Earth's most powerful winds hit only about 250 miles per hour. Pretty cool planet A. Yeah, and it's my favorite planet too. So let's dive into the story of how Neptune was discovered. Oh, and listeners, just so you know, most of the story I'll be sharing next comes directly from the wiki entry, though I do paraphrase here and there. Interestingly, some astronomers had observed Neptune prior to 1846, but they didn't know it was a planet.

12:32Galileo's drawings of his observations indicate that he observed Neptune on December 28, 1612, and again on January 27, 1613. At the time of his first observation in December 1612, it was stationary in the sky because it had just turned retrograde that very day. This meant that Neptune's motion was too slight to be detected, and its apparent size was too small to appear clearly as a planet in Galileo's small telescope. However, there is evidence that Galileo was aware there was something unusual about this star. On January 28, Galileo recorded in his notebook that a background star, Neptune, had appeared to move, and drew its position with a dot in a different colored ink to the fixed stars. This suggests that Galileo had compared his January 28 observation to an earlier sketch drawn

13:38on the night of January 6, which would indicate a systematic search among his earlier observations. Unfortunately, there is no clear evidence that he identified this moving object as a planet. Nor did he ever publish these observations or attempt to observe the moving source again. Sears Walker of the US Naval Observatory searched historical records and surveys in 1847, specifically looking for possible pre-discovery sightings of the planet Neptune. He found observations made in 1795 by Michel Le François de La Lance staff at the Paris Observatory that those observations were in the direction of Neptune's position in the sky. In the catalog observations from May 8, and again on May 10, 1795, a star was observed

14:39in the approximate position expected for Neptune. The uncertainty of the position was noted with a colon. This colon notation was also used by Le Lance staff to indicate an observation error. So, it was not until after the original records of the observatory were reviewed that it was identified as Neptune, and that the position error in the observations made two nights apart was due to the planet's motion across the sky. In 1830, John Herschel almost discovered Neptune the same way his father William had discovered Uranus back in 1781 by a chance observation. In an 1846 letter to Wilhelm Strue, John states that he observed an object during a sweep of the sky on July 14, 1830. Although his telescope was powerful enough to resolve the object into a small blue disk,

15:45he did not recognize it as a new planet at the time and mistook it for a star. So listeners, you may be thinking, what prompted Le Vary a to undertake the pain stakingly complicated calculations that predicted where Neptune could be seen in a telescope? I'm so glad you asked, here's what I read. Quote, in 1821, French astronomer Alexis Bouvard published astronomical tables for the orbit of Uranus, including predictions of future positions based on Newton's laws of motion and gravitation. But subsequent observations revealed substantial deviations from the location predictions in his tables. This led Bouvard to hypothesize about the irregularities that were observed in both the planets' ecliptic longitude and in its radius vector, or distance from the Sun.

16:49Among his hypotheses were A, the effect of the Sun's gravity at such a great distance might differ from Newton's description, B, the discrepancies might simply be observational ever, or C, perhaps Uranus was being pulled or perturbed by an undiscovered planet. Meanwhile, across the channel, prior to 1843, British astronomy student John Couch Adams learned of these irregularities while still an undergraduate and became convinced of the perturbation hypothesis. These believe that he could use the observed data on Uranus and Newton's laws of gravitation to deduce the mass, position, and orbit of the perturbing body. After his final examinations in 1843, Adams was elected a fellow of his college and spent

17:52the summer vacation in Cornwall beginning his calculations. In modern terms, it's an inverse problem, an attempt to deduce the parameters of a mathematical model from observed data. Although the problem is a simple one for modern mathematics and electronic computers, at the time, it involved, during the time of Adams' work, it involved much laborious manual calculation. He began by assuming a nominal position for the hypothesized body using the empirical BODES law. He then calculated the projected path of Uranus, given the assumed position of the perturbing body, and then computed the difference between his projected path and the recorded observations of Uranus. Next, he adjusted the characteristics of the perturbing body based on these differences

18:54and repeated the process, essentially performing a regression analysis. Then, on February 13, 1844, James Chalice, director of the Cambridge Observatory, contacted astronomer Royal George Biddle Erie at the Royal Observatory in Gretich and requested data on the position of Uranus for Adams. On September 1, 1845, Eugene Bovard, Alexis Bovard's nephew, presents new tables of Uranus to the Paris Academy. And on September 22, Francois Arrigo of the Paris Observatory asked Herbain L'Avériee to investigate the Uranus orbital perturbations. I know, I know, listeners, you're thinking, wait, who was that John Couch Adams? I thought you said L'Avériee sent his calculations to Gala for observations.

19:58Well, yes, I did. But while Gala carried out his telescopic observations using L'Avériee's calculated data, the young British astronomer Adams had performed calculations also, calculations that weren't made public until after Gala's observation and didn't result in a confirmed planet sighting. And this, my dear listeners, is at the heart of the sticky wicket. So let's get back to that timeline. On November 12, 1845, Adams finds a solution to his radius vector problem, but he doesn't know that L'Avériee is working on the same problem. The following year on June 1, 1846, L'Avériee presents his first location prediction to the Paris Academy for an object perturbing Uranus's orbit.

20:59By the 23rd of June, George Biddle-Ari in Britain receives L'Avériee's first prediction. At a July 1846 meeting of the Board of Visitors of the Greenwich Observatory with Chalice and Sir John Herschel present, Ari suggested that Chalice urgently look for that planet with using the Cambridge 11.25-inch equatorial telescope. The search was begun by a laborious method on July 29. Adams continues his calculations, providing the British team with six solutions from his work in 1845 and 1846, which sent Chalice searching the wrong part of the sky. Only after the discovery of Neptune had been announced in Paris in Berlin, did it become apparent that Neptune had been observed by Chalice on August 8 and August 12.

22:03But because Chalice lacked an up-to-date star map, it was not recognized as a planet. So back on the timeline, the following month on August 31, L'Avériee publishes his final prediction that also includes both mass and orbit for the new predicted body. On September 2, Adams sends his first letter on his predicted location to Ari, George Biddle Ari, but does not publish. Meanwhile, over in France, no one at the Paris Observatory is looking for the predicted planet. So, on September 18, 1846, L'Avériee writes to his colleague Gala at the Berlin Observatory. On the very day he receives the letter, which was the 23rd of September. Gala begins his observations.

23:03And thanks to a suggestion by Darest, they use as a reference a newly published sky chart, the Hora XXI. Listeners, it was the Roman numerals of Skychart, was Hora 21 and they did the Roman numerals. Okay, at 15 minutes after midnight on the 24th, Gala and Darest found the planet using the frown Hofer Telescope in a location only one degree different from L'Avériee's prediction. Woohoo! Over the next two evenings, a proper motion of the celestial object of four seconds of arc was measured, which confirmed it as a planet. Gala always refused to be acknowledged as the discoverer of Neptune. He attributed the discovery to L'Avériee. On September 29, Jorffbittl Erie hears news of the new planet while on vacation in Germany.

24:07Chalice gets the news on the 30th. And that same day John Russell Heind is the first Englishman to observe it. On October 1, L'Avériee sends letters to European observatories announcing the name Neptune. Also on the first Heinds letter announcing the new planet, the same new planet is published in the Times of London magazine. By the 11th of October, L'Avériee's final theory is published in, and I apologize to the listeners, I'm going to probably mispronounce this, Astronomisch Nakatrichtin. This translates as astronomical notes and is claimed as being the oldest astronomical journal ever. Ok, so then on October 17, Chalice and Adams proposed the name Oceanus for the new

25:09planet. On the 19th of October, Erigo, over in France, addresses a stormy meeting at the Academy of Sciences in Paris. A month later, on November 13, Adams calculated predictions are finally revealed at a meeting of the Royal Academy of Sciences with Adams, Chalice, and Erie in attendance. Ho-ho, a keen controversy arose in France and England as to the merits of the two astronomers. Adams and L'Avériee. Adams was a definite young man who was naturally reluctant to publish a result that would establish or ruin his career. Erie and Chalice were criticized, particularly by a James Glacier, for failing to exercise their proper role as mentors of a young talent. Chalice was contrite, but Erie defended his own behavior, claiming that the search for

26:10a planet was not the role of the Greenwich Observatory. In France, the claims made for an unknown Englishman, Adams, were resented as detracting from the credit due to L'Avériee's achievement. Though some claim the French themselves found L'Avériee to be arrogant and assertive. Interestingly, the Royal Society awarded L'Avériee the co-plie medal in 1846 for his achievement without any mention of Adams. As the facts became known, some British astronomers pushed the view that the two astronomers had independently solved the problem of Neptune and ascribed equal importance to each. But Adams himself publicly acknowledged the L'Avériee's priority and credit, not forgetting to mention the role of Chalicee in the paper that he gave to the Royal, he being Adams,

27:12gave to the Royal Astronomical Society in November of 1846. More recently, in 1999, Adams correspondents with Erie, which, and get this listener, it had been lost by the Royal Greenwich Observatory. But was rediscovered in Chile. That's right, I said, Chile, you know, South America, among the possessions of astronomer Olen J. Egan after his death. And in a 2003 interview, British historian Nicholas Collestrom concluded that Adams claimed to Neptune was far weaker than had been suggested, as he had vacillated repeatedly over the planet's exact location with estimates ranging across 20 degrees of arc. Others who have reviewed both sets of predictions acknowledged that Adams's were not as close as L'Avériee's to the actual observed location for Neptune.

28:17But I don't recommend getting too drawn in by Collestrom's further exploration of the issue. And I'm only going to tell this short story about Collestrom because I think it's important for you listeners, especially for your young researchers, that when you read something, always look at the references and look into who's writing that article and try to get a feel for what their viewpoint or what their agenda might be because sometimes you will be surprised. If we look closer at him, which I did, we discover a person with a burgeoning penchant for stirring up controversy. Back in 1999, this mostly newly minted PhD science historian received a grant from the Royal Astronomical Society to work on the classification of correspondence related to this. This discovery of Neptune, and he and his co-authors have an article in the December 2004

29:19Scientific American describing how the British had wrongly taken credit. According to them, while the attempt to take credit started with James Chalice and George Biddle Erie, subsequent to Gala's observation, it was promulgated by five English historians and or astronomers who wrote on the subject between 1852 and 1947, noting that each of the five authors were at some point president of the Royal Astronomical Society, and Albert One were from either Trinity or St. John's College, which was Adams's alma mater, and it goes on from there. But do keep in mind, Collestrom himself took a hard right turn from mainstream science around that same time, and became involved in quite a number of strange, highly controversial and political subjects, one of which got him sacked from University College London in

30:222008 for engaging in Holocaust denial propaganda. Yikes! So, regardless of those whose agenda is to drag us down rabbit holes, what can we conclude from all the published through Ha Ha concerning the discovery of Neptune? Well, first of all, the controversy was a long time ago. Second, the mathematical prediction for the location of a new body in the outer solar system was a great intellectual feat, calculated with more precision by Le Vierier, who was more experienced than Adams at the time. Gala and Darest also deserve accolades for immediately diving in and looking for the new planet. Chalice is on record expressing his regret at not searching sooner, and for not having

31:27an up-to-date star chart. And one thing I found interesting in my reading is this. These prediction calculations showed that Newton's law of gravitation, which Erie had almost called into question, prevailed even at the limits of the solar system. Oh, and don't forget that it is still an issue today that scientific research teams want to get credit for publishing something new and earth-shattering before their competition does. Ha Ha! Now, wasn't that a good story? Please stay tuned for our next episode in November when you'll hear my interview with the winner or winners of HAD's 2027 Oster Brock Book Prize. We don't know who's won yet, and I can't wait to find out. I'd like to thank the folks at CosmoQuest and the folks with Patreon who generously support

32:28365 days daily podcasts, including ours. Thank you. Now, if you're curious about any of the people or science discussed today on the 365 days webpage for this episode, click on the Read More button to access episode information that includes the transcript in which I write a list of links for fun, facts, and further reading. And, though I am continuing to post the podcast transcripts on my LinkedIn page, I learned earlier this year that the suits that manage LinkedIn had their teenage computer programmer's make it so that you can no longer download PDF documents from a person's page I am so sorry. Well, that's all for now. Thank you for listening. Goodbye. You're listening to the 365 Days of Astronomy Podcast. Cool. The 365 Days of Astronomy Podcast is produced by the Planetary Science Institute.

33:48Audio post production is by me, Richard Jerome. Project management is by Aviva Yamani, and hosting is donated by libson.com. This content is released under a Creative Commons Attribution Non-Commercial 4.0 International License. Please share what you love, but don't sell what's free. This show is made possible thanks to the generous donations of people like you. Please consider supporting our show on patreon.com, forward slash CosmoQuestX, and get access to bonus content. Without your passion and contribution, we won't be able to share the stories and inspire the worlds. We invite you to join our community of storytellers and share your voice with the listeners worldwide. As we wrap up today's episode, we're looking forward to unraveling more stories from the universe. With every new discovery from ground-based and space-based observatories and each milestone and space exploration, we come closer to understanding the cosmos and our place within

34:52it. Until next time, let the stars guide your curiosity.