A compilation of episodes all about the history of space exploration.Discover our full back catalogue of hundreds of videos on YouTube: https://www.youtube.com/@astrumspaceFor early access videos, bonus content, and to support the channel, join us on Patreon: https://astrumspace.info/4ayJJuZ
Chapter 1: What led to the discovery of Neptune?
However, being overzealous could lead to being remembered for all the wrong reasons. I'm Alex McColgan and you're watching Astrum, and in today's video we're going to be looking at the fascinating discovery of a planet in our solar system closer to the Sun than Mercury. It was observed dozens of times by various astronomers. The only problem? It doesn't actually exist.
Let's rewind to the year 1846, when something astounding had just happened in the scientific community. A bon Jean-Joseph Le Ferrier, a French astronomer and mathematician, had just helped discover the planet Neptune using nothing but pure mathematics. He had been examining the rotation of the, then, seven planets when he noticed that something was off about Uranus.
It didn't seem to be moving in line with the theories of gravity proposed by Newtonian physics. Le Verrier reasoned that the only explanation for this was that there must be a planet out beyond the orbit of Uranus that was perturbing its motion to account for this discrepancy. He did some maths, and then declared that his eighth planet must exist at an exact point in the night sky.
The incredible thing was, after hearing his prediction, Le Verrier's friend, Johann Gottfried Galle, got out a telescope, searched in that location, and sure enough discovered the planet Neptune in a single hour. It was almost exactly where Le Verrier had predicted that it would be.
The scientific community went wild with this discovery, and Le Verrier was rightly celebrated for his incredible deductions. So it's not surprising that a decade later, when he predicted the location of a ninth planet using the same methodology, the scientific community listened. In fairness, he had not been the first to predict that such a planet existed.
It was as far back as 1601 that German astronomer Christoph Scheine had claimed to have noticed a strange black spot moving in front of the Sun, and had claimed that this was a planet. In reality, it was most probably a sunspot. Other alleged sightings had been made throughout the years. Kapel Loft in 1818,
Franz von Greutheusen in 1819, J. W. Pasdorff between 1822 and 1837 all claimed to have seen an object or objects orbiting the Sun. Pasdorff claimed to have seen it at least 12 different times. People had even begun to spitball a name for this hypothetical planet. In 1846, French astronomer Jacques Babinet suggested calling it Vulcan, after the Roman god of volcanoes, fire and metalwork.
This would have been an appropriate name, as any planet closer to the sun than Mercury would have been exceptionally hot. Mercury already experienced temperatures of 427 degrees Celsius. Vulcan would have been even hotter. And yet, for all these sightings, confirmation of the planet remained elusive. But what made Le Verrier's claim stand out was the way he had come to make it.
In 1845, before his discovery of Neptune, Le Verrier had been asked by the director of the Paris Observatory to apply Newton's laws of physics to the orbit of the planet Mercury, to see if the two lined up. Le Verrier did so, laying out a theoretical orbit that Mercury would take around the Sun based on Newtonian physics.
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Chapter 2: What was the significance of the predicted planet Vulcan?
He got to speak at meetings of learned scholars. There was only one problem. The planet he had discovered didn't actually exist. There were numerous proofs of this. For one, naturally, other scientists wanted to take a look at this new planet Vulcan.
Le Verrier calculated from Lescarbeau's observations that Vulcan must orbit 21 million kilometres out from the Sun and did so every 19 days and 17 hours, so it would be easy to spot, as it would be calculable when it would pass the Sun again next. Astronomers pointed their telescopes towards the Sun at the appointed time, but Vulcan was a no-show.
Le Verrier was troubled by this, but by then more reports were coming in of the planet's sighting. Other astronomers were going back through their records, and were matching up phenomena they had seen with the new planet Vulcan.
Some of these were years out of date, and not even listed as to when in the year they had happened, but Le Verrier still used these to tinker with his model, reasoning that perhaps his maths were just out. So he would predict, and would not see Vulcan, and would rework his theory, and would not see it again. Another piece of damning proof came from Emmanuel Lieu, another French astronomer.
Lieu claimed that he had been coincidentally looking at the Sun at the exact moment Lescarbol had with the twice as powerful telescope, and had not seen the planet Lescarbol had claimed to have observed. Vulcan's existence floated through murky waters, as there were renowned scientists who did claim to see it from time to time.
Le Verrier died in 1877, but just a year later in 1878, two well-renowned astronomers both claimed to have seen Vulcan at the same point in the sky at the same time during a solar eclipse. They even both claimed that the planet was reddish in colour. The corroboration was compelling, yet Vulcan still did not exist. In science, if a fact is true, then it is repeatable.
And in spite of all these observations throughout the years, Vulcan was never repeatedly observed. It was never seen during a solar eclipse again. In time, that corroborated sighting was put down to calculation errors and misidentifying a known star. But ultimately, the one who finally put the idea of Vulcan to rest was Albert Einstein, and he did so by thinking of something completely different.
Numerous scientists over the years had attempted to see Le Verrier's planet Vulcan, because mathematically, they were certain it had to exist. Newtonian physics demanded that it did. They strained to see it, and in that confirmation bias, they did see it, again and again, just never in the same place. But Einstein realised that it was Newtonian physics that was at fault.
In 1915, he proposed a model of physics that accurately described the motion of the universe, but relied on things like curvature of spacetime rather than gravity. At slow speeds, it looked a lot like Newtonian physics, but when you placed objects like Mercury next to very massive objects like the Sun, Special relativity predicted a different path for their orbits.
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Chapter 3: How did the scientific community react to the discovery of Vulcan?
The 28th of October will mark the 50th year anniversary of the launch of this special satellite, and although it no longer functions, it will likely remain in orbit for another 50 years yet. There is something strangely sad about this unique satellite that only ever ran a couple of scientific experiments, yet we can learn inspiring lessons from its story. But why is it unique?
Prospero is the result of the only time a nation developed its own rocket capacity to put a satellite into space, and then later discarded that capability. I'm Alex McColgan and you're watching Astrum. Join with me as we uncover the early days of space exploration history of my home nation, and the first and only time they put a satellite into space using a rocket of their own making.
Today we will be exploring Prospero and the Black Arrow program of the United Kingdom. The UK officially joined the space race in 1962 when they became the third country to operate a satellite in space after Russia and the United States. However, that satellite, Ariel-1, was not launched using a UK rocket, but was instead carried into orbit by NASA.
And as America and the USSR were starting to gear up for their journey to the moon, the United Kingdom was eager not to be left behind. The Royal Aircraft Establishment, which was the closest equivalent the UK had to their own space agency at the time, first proposed the idea of developing their own rockets in 1963. Up until then, UK rocket science was mostly military in nature.
Blue Streak and Black Knight rockets were developed using the scientific knowledge of German scientists who'd been brought to Britain after World War II, much like what happened in America around the same time, and they were intended to carry nuclear payloads. However, the RAE wanted to make rockets carry satellites into space for scientific and communication purposes.
Their initial request was for a low Earth orbit rocket that could carry a 144kg satellite into orbit. The request was approved in 1964, but was quickly put on hold due to an upcoming general election. A new government came in and restarted the process, but decided to reduce the number of test flights from 5 to 3.
This was the beginning of the slow withering of the UK's rocket abilities, before they had even really begun.
Using the technology of the Black Knight rockets, RAE scientists began to develop the Black Arrow, a three-stage rocket that, although it used a lot of the same technology as the Black Knight, was considerably more powerful, producing an initial 256kN of thrust compared to the Black Knight's 96kN.
The first stage would carry the payload for the first two minutes or so of the launch, before falling away. The second stage would burn for two more minutes, before splitting in half, releasing the third stage and the payload. After separation, the third stage would burn for a minute, and a minute later again, the payload and final stage would separate.
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Chapter 4: What were the challenges faced by the Black Arrow program?
Astronauts would also need to practice doing spacewalks, in case work on the outside of a spacecraft became necessary during transit. And finally, more practice would be needed with re-entry techniques, particularly touching down at a pre-selected location on land, although in the Apollo missions this last idea was dropped.
On top of that, the Soviet Union was ahead, and America needed to catch up. So while the Apollo team set to work developing its rockets and modules, these extra challenges were handed off to a support mission to work out. The mission was given the name Project Gemini. Project Gemini, which launched 12 missions between 1961 and 1966, built on the foundations of Project Mercury.
The Gemini capsule was essentially a larger version of the one used on Mercury, now able to hold a crew of two. The rocket used was a Titan II, another adapted military missile redesigned for a new purpose of discovery. Gemini also saw an expansion on that technology. For Project Mercury, the Mercury spacecraft could do little to redirect itself once it made it into orbit.
If a space rendezvous was going to happen, this would need to change. The Gemini spacecraft was given an orbit attitude and manoeuvring system to allow it to change its orbit and orient while in space. The Gemini spacecraft was also developed to be able to support a crew in space for longer. By the launch of Gemini 5, astronauts were able to spend an entire week in space.
To play it safe, in later flights this time was extended to 14 days by Gemini 7, six more days than would be required for a trip to the moon. While there was a lot of success with these missions, there were some scares too. Neil Armstrong flew on Gemini 8. The purpose of this mission was to meet up with and dock with an uncrewed Agena target vehicle which had been launched earlier.
The first part of the mission went smoothly, with the docking being a success. But while Armstrong and his co-pilot David Scott were still in the target vehicle, they noticed that the ship had started spinning in space. This could be catastrophic. If the spinning ship hit their Gemini ship while the two attempted to undock, it could cause fatal damage to their craft.
Furthermore, they were not exactly sure why the craft was spinning. If a thruster was firing when it shouldn't be, then it would be using up valuable fuel, fuel that was needed to orient themselves for the correct way for re-entry. If they were not facing the right way, the heat shield would not protect them from the incredible heat generated.
The two astronauts worked quickly, and by firing one of the opposing thrusters, they were able to slow the two crafts enough that they were able to get back into the Gemini craft and just about undock safely. They realised then that it had been one of the Gemini craft's thrusters that had been firing.
Both astronauts were close to passing out, however they managed to fix the fault, and using the re-entry thrusters, Armstrong calmly got the craft back under control, stopping his tumble. He managed it, with only 30% fuel remaining. Moments like this reinforce the importance of being able to perform EVAs, or extravehicular activities.
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Chapter 5: What were the key missions of Project Mercury?
The airbags were heavily worn, and that leaky snorkel valve from earlier was also allowing water in. By the time the capsule was rescued, it had taken in roughly 360kg of water on board. After a three-hour recovery, the capsule and its precious cargo were airlifted to the nearest Navy ship, when NASA scientists waited on Han to see the fate of Ham.
A lot had gone wrong with this mission, but was he still alive after all of that? And if so, what state was he in? Scientists and Navy personnel worked quickly to get him out, The cover came off and Ham was… fine. He had done it, and he was safe and well, still his happy self, almost as if nothing noteworthy had happened.
He survived everything relatively unscathed, his only injury was a bruised nose. Hamm retired from spacefaring shortly thereafter and lived a good 20 years after his voyage in a number of zoos. He passed away in 1983. His skeleton was sent to the US National Museum of Health and Medicine. His other remains buried and honoured by the International Space Hall of Fame in New Mexico.
because of the success of this mission. A few months later, the US successfully sent Alan Shepard into space on board another Mercury-Redstone rocket, called Freedom 7. However, the US didn't win this space race. The Soviets successfully orbited around the Earth with a human on board called Yuri Gagarin aboard Vostok 1.
But the legacy of this mission can still be felt today, with humans now on board the International Space Station, and even now with a space race to get humans on the moon a second time. So, there we have it, the story of the chimp who beat all humans to space, Ham. In 1977, two pioneers embarked on what might be one of the most epic feats of exploration ever undertaken. Their goal?
To unravel the cosmic mysteries surrounding the solar system and our place in it. Not only did they provide us with some of the first and best imagery of our solar system's outer planets, but they continued to send us incredible new information about our universe from interstellar space, some 47 years and 24 billion kilometers later.
The Voyager 1 and 2 probes are more than just instruments and circuitry. They are a symbol of humanity at its best. Curious, audacious, ambitious and resilient. Voyager didn't just capture dazzling photos of our gas giants and their moons. It captured the hearts and minds of generations back home on Earth. When I look back,
I realised how little we actually knew about the solar system before Voyager," says Voyager mission project scientist Edward Stone. We discovered things we didn't know were there to be discovered, time after time. I'm Alex McColgan and you're watching Astrum.
Join me today as we trace Voyager's iconic journey in pictures, from the splendour of Jupiter, to Saturn's icy rings, to the topsy-turvy world of Uranus, to the mighty storms of Neptune. We explore what this mission taught us about our planetary neighbourhood. On the 20th of August 1977, NASA launched the Voyager 2 space probe from Cape Canaveral, Florida.
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Chapter 6: How did Project Gemini contribute to space exploration?
This data was suggested by Voyager data, but it wasn't until we flew Cassini out there that we could confirm it to be true. Further geological data and imaging shows that Enceladus' terrains are an unexpected mixture of old and new. The left side, which appears smooth, is the newer side, and the right side, with densely packed impact craters, is the older side.
This suggests Enceladus is a very geologically active moon, which it wasn't previously thought to be. Before we make our way to the wonky world of Uranus, we have to say goodbye to Voyager 1. After its flyby of Titan and Saturn's rings, its path was bent upward out of the ecliptic plane. From here, the probe headed straight for interstellar space.
Of course, it would be another 32 years before it would reach that. But not to worry, Voyager 2 took a slingshot around Saturn instead, to propel it on to Uranus and Neptune. These would be the first and only flybys of the planets in human history. Five years after arriving at Saturn, NASA's Voyager 2 arrived on approach to Uranus in January 1986.
At its closest, the probe came within 81,500 km of Uranus' cloud tops. Voyager 2 revealed an absence of visible cloud features in Uranus' atmosphere. Unlike Jupiter and Saturn, Uranus displayed a serene, featureless cloud deck, challenging scientists' preconceptions about the atmospheric dynamics of gas giants.
The false colour image on the right brings out the subtle differences in the atmosphere of the polar regions, which are tilted on a 98 degree axis. But it was another tilt that stunned Voyager scientists. It was previously unknown whether Uranus had a magnetic field, but Voyager data showed us that not only does Uranus indeed have a magnetic field, it is also tilted at an astonishing 59 degrees.
That means its magnetic and rotational poles are not at all in the same place. Until then, it was thought that these poles were always aligned. It certainly is here on Earth, our magnetic and rotational poles are only shifted by 12 degrees. The stark deviation found on Uranus defied conventional planetary magnetic field models and forced scientists to rethink their assumptions.
One side effect of this misalignment of poles is that as the planet spins, its magnetosphere, the space carved out by its magnetic field, wobbles like a poorly thrown football. Scientists still don't know how to model it, but it might look something like this. Voyager 2's observations unveiled more details about the known rings of Uranus, and discovered two more.
It is the first to capture images of these dark rings, like its outermost ring visible in this photo. The rings are composed of fine dust particles, Voyager 2 also discovered two Shepard moons orbiting one of the newly discovered rings, similar to its findings with Saturn's to the F ring. Here they can be seen from 4 million kilometres in a photo from the 21st of January 1986.
This mission significantly increased the known count of Uranian moons. Prior to Voyager 2, we only knew about 5 moons orbiting Uranus. Voyager 2 sent us the first ever images of these moons, which you'll see in a second, but it also discovered 11 more moons, bringing the total to 16 moons.
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Chapter 7: What was the impact of the Apollo program on space travel?
every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species lived there on a moat of dust suspended in a sunbeam. This sentiment rings with as much power today as it did 33 years ago.
Both Voyagers 1 and 2 are still operational today, though Voyager 1 is experiencing a bit of a tech glitch at the moment. Still, an incredible feat that we've managed to get both probes into interstellar space further than any other man-made device. Provided this glitch can be fixed, the probes are estimated to remain viable for a few more years before running out of power and going dark forever.
While we aren't certain what these pioneering probes will encounter in the depths of space, we can be sure that the incredible images they provided back home have inspired generations of scientists, engineers, stargazers and dreamers. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world.
To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known. Thanks for watching. I was honestly blown away by all the incredibly kind comments and messages you've sent me, and by the numbers of you that signed up to the Patreon.
Like I said in the replies to your DMs on Patreon, everyone here at the Astrum team is so grateful to have such an amazing community. If you haven't joined the Patreon party yet, we're still on our long-term thousand patron member drive, so you can go to the link in the pinned comment to become a part of that effort.
When you join, you'll be able to watch the whole video ad-free, see your name in the credits, and submit questions to our team.
Meanwhile, click the link to this playlist for more Astrum content. I'll see you next time.
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