Holst’s Planets: where astrology and astronomy collide! (Part Two)
— Paul Cornish, Assistant Planetarium Producer
Part One can be read here!
Last week I began attempting to stave off my yearning to get back into the We the Curious Planetarium by investigating the science and history behind one my favourite Planetarium Shows — Holst’s Planets 3D. (Read Part 1 here!) The show involves Gustav Holst’s famous seven-movement orchestral suite played over specially created 3D visuals of the Solar System. A member of our Planetarium Team (sometimes me!) controls the visuals in a live performance in front of an audience.
I began to examine the images conjured by Holst’s music, and the astrological beliefs of the composer that inspired the show. Holst was a devotee of Alan Leo, “the father of modern astrology” and so I began to compare the astrology evident in Holst’s music, and Leo’s book ‘The Art of Synthesis’ to see if there were any parallels between them and modern astronomy. There were little similarities to be found in Mars and Venus, but maybe we’ll have more luck with the rest of the Solar System?
Jupiter
“Jupiter governs a combination of feeling and thought. It includes humanity, benevolence, compassion, honour, candour, good humour, and the higher moral and social qualities.”
“The planet Jupiter is especially related to the magnetic aura that surrounds every living creature.”
“Jupiter may be said to represent the aspect of power, of harmoniously balanced expansion, growth; that which urges evolution.”
Alan Leo, 1912
Holst echoes Leo’s image of Jupiter as governing “benevolence,” “good humour,” and “harmonious balanced expansion” with his majestic and uplifting movement. Looking at what we’ve learned from Jupiter over the years it seems that they weren’t too wide of the mark.
Gas giant Jupiter is certainly majestic and powerful — it’s the largest planet in our Solar System. Over 1300 planet Earths could fit inside it.
It’s notable that Leo described Jupiter’s relation to the “magnetic aura that surrounds every living creature” as Jupiter has a magnetic field that’s fourteen times as strong as Earth’s. Just like on Earth, this magnetic field is a big factor in the existence of beautiful lights in the vicinity of the northern and southern poles — the aurorae. On Earth these aurorae are caused by charged particles from the Sun interacting with Earth’s magnetic field. On Jupiter the aurorae are believed to be caused by other factors — for example, the plasma produced by the volcanic moon, Io and the transport of this plasma within the planet’s magnetic field — as well as by charged particles from the Sun. When presenting the show I can display Jupiter’s aurorae in all their glory.
Jupiter could also be seen as the “benevolent” host of 79 known moons, although “harmoniously balanced” might not be an accurate description of their wonky orbits. Eight of Jupiter’s moons are regular moons that move in the same direction as the planet’s rotation and roughly along its equatorial plane. But the rest are irregular moons that are much more distant from Jupiter. Many of them move in the opposite direction to Jupiter’s rotation and at different angles to its equator. The regular moons most likely formed long ago from a ring of gas and solid debris around Jupiter, while the irregular moons probably once orbited the Sun but were snatched into orbit around Jupiter by the planet’s gravity. The orbital paths of Jupiter’s moons can also be displayed during the show.
These moons aren’t the only thing orbiting Jupiter. In 2016, after a journey of 2.8 billion kilometres that lasted five years, the NASA space probe Juno reached Jupiter. Since then Juno has been swooping close to the planet every 53 days, investigating its gravity and magnetic fields, and searching for clues about how the planet formed. Among Juno’s scientific instruments is a colour camera called JunoCam. Over the past four years it’s sent back some stunning images. It’s given us a closer look at Jupiter’s swirling storms, including the Great Red Spot, a gigantic storm, more than twice the size of Earth! Many of the images captured by Juno can be displayed during the show.
Saturn
“Saturn is the most important planet in all horoscopes…marking the critical stage between the real and unreal, the true and the false, the subjective and objective, light and dark, good and evil.”
“Where Mars is passional and impulsive, Saturn is slow, cold, and deliberate.”
Alan Leo, 1912
Leo’s description of Saturn as a “slow, cold, and deliberate world” is certainly conveyed by Holst’s music, but may not be a truly appropriate description of the planet. Saturn could be described as slow when compared to Earth. After all, Saturn orbits the Sun once every 29.4 Earth years. But when it comes to rotational speed, Saturn is a lot more speedy — it takes 10 hours and 34 minutes to turn on its axis.
Saturn is also home to some extremely fast winds. During the show our presenter has the option of focusing on the Rose (also known as the Hexagon) — a storm that’s twice the size of planet Earth. It surrounds Saturn’s north pole and has winds that blow at more than 500km per hour — faster than Earth’s strongest hurricanes.
If “slow” isn’t the best description of Saturn, then neither is “cold”. Saturn averages 1.4 billion km from the blazing heat of the Sun — nine and a half times Earth’s average distance. But its interior is very hot, reaching temperatures of up to 11,700°C.
As for being “the most important planet”, it depends on what you mean by important. It’s not the biggest planet — that honour belongs to fellow gas giant, Jupiter — but it’s still very big. Over 800 planet Earths could fit inside it. Saturn does have more known moons than Jupiter, although this was a title it only won recently. In 2019 20 new moons were discovered orbiting Saturn, bringing its total of known moons up to 82 — three more than Jupiter.
If Saturn does have a greater claim to importance than the other planets, it’s probably because of its magnificent rings. All the gas giants have rings, but Saturn has the most extensive ring system of any planet in our Solar System. In terms of size, if Earth were at the inner edge of Saturn’s rings, the Moon would be at the outer edge. These mighty rings are so famous they have made the image of Saturn synonymous with our Solar System, and astronomy in general. The rings are made from trillions of pieces of ice, with some rock too. Most are so small you could hold them in your hand. A highlight of the show for me is flying through the rings and seeing these trillions of pieces up close.
Uranus
“Uranus governs the Will in the highest degree, and it can be associated equally with thought, feeling, and action… It makes thought active, original, ingenious, and powerful.”
“(Uranus) is a planet of great power and energy and may be compared in some respects to chemical explosives.”
“Like a violent explosive we have to look upon (Uranus) as containing an unusually large quantity of energy, apparently ready to exert its characteristic effects suddenly and on slight provocation.”
Alan Leo, 1912
Holst’s Uranus is confident, energetic, and enthusiastic. The piece reflects Leo’s description of a world with an “explosive” influence. But Uranus is far from “explosive” or “energetic”. It is in fact an ice giant. That doesn’t mean that the planet is a huge ball of solid ice. Most of its mass is a hot, dense fluid of “icy” materials — water, methane and ammonia — above a small rocky core.
Uranus has the coldest atmosphere of any of the planets in the Solar System and its internal heat appears to be lower than that of the other giant planets. We’re not sure why Uranus is colder than Neptune, despite Neptune being further from the Sun. One possible explanation is that a long time ago Uranus was hit by something huge from space — maybe a rock the size of the Earth, which caused it to expel most of its heat, leaving it with a depleted core temperature. This could also explain why Uranus rolls around the Sun on its side, relative to the other planets (my favourite Uranus fact).
Holst’s Uranus is cheerful in tone, but in fact Uranus is a lonely world that has only ever had one visitor, way back in 1986. An inspiration to us all in this period of social distancing. Voyager 2, who remains the only spacecraft to ever visit Uranus, discovered a lot about the planet, including the existence of 10 moons. Since then more moons have been discovered orbiting the planet, and today we know of 27. While presenting I have the option of displaying Voyager 2 during the show and of sharing some of the images that the probe captured of Uranus.
I can also take the audience through the rings of Uranus. Uranus has at least 13 rings that we know of. They’re made from countless pieces of water ice and probably formed when two moons of Uranus collided, and smashed apart. They’re quite young, around 600 million years old. That’s old to us but compared to some of the other stuff out there in space those rings are in the first flush of youth.
Neptune
“Neptune is supposed to be the planet of Chaos, representing a state of things undifferentiated, disordered, without shape or definite form.”
“Unstable as water is suitable description of Neptune, unstable, constantly changing, unreliable, and not to be depended on.”
Alan Leo, 1912
Holst’s Neptune, with its use of an eerie sounding choir, reflects the mysterious, nebulous and ever-changing qualities described by Leo. Neptune is indeed a mysterious world. At an average distance of 4.5 billion kilometres from the Sun, Neptune is the most distant planet in our Solar System and we still have much to learn about it.
Despite this, we have managed to learn a few things about Neptune over the years. It was first observed through a telescope in 1846, but its existence was known of before that. A French astronomer named Alexis Bouvard was able to predict Neptune’s existence from observing changes in the orbit of Uranus. These changes led him to believe it was being affected by the gravity of another planet. Other astronomers were then able to use Bouvard’s observations to calculate Neptune’s position.
Far from being as “unstable as water”, Neptune is an ice giant, just like Uranus. The methane in its atmosphere is what gives the planet its distinctive blue colour. During the show I like to take the audience down into this gassy, blue atmosphere.
The surface of Neptune has even been photographed by a space probe. In 1989, Voyager 2 sent back our first photos of a Great Dark Spot on the surface of Neptune. A Great Dark Spot is another potential destination in the show. Great Dark Spots are big storms — about the size of Earth — that tend to last just a few years before fizzling out. It’s then never long before another one develops somewhere else on the planet. It’s thought that the storms could actually be gaps in the upper atmosphere of Neptune, allowing us to peer through the blue methane gas and glimpse deeper into the planet.
Beyond the Planets
“Neptune is the remotest planet of our solar system known to physical science, although it is believed by many occultists that two more lie beyond…They must therefore dominate senses of which at present we can have no conception, states of being and existence which have not as yet dawned on us.”
Alan Leo, 1912
As interesting as they are, most of the parallels between the writings of Alan Leo and modern science are coincidental. Leo’s astrological beliefs about the Solar System are largely at odds with our modern scientific understanding. But to his credit, Leo knew that there were things out there that we have yet to discover - beyond the planets.
Since Leo wrote ‘The Art of Synthesis’ we’ve learned a lot more about the farthest reaches of our Solar System. We’ve discovered five dwarf planets in our Solar System — Ceres is in the Asteroid Belt between Mars and Jupiter, while Haumea, Makemake, and Pluto are beyond Neptune. There may be many more dwarf planets waiting to be discovered.
We now know that our Solar System is surrounded by the Oort Cloud — a shell of icy bodies that stretch out an incredible nine trillion kilometres from the Sun. That’s a quarter of the way to the next nearest star!
Voyager 2, and its twin probe Voyager 1 are still travelling away from us. In 2012, Voyager 1 left the Solar System and reached interstellar space. It is the first object made by humans to do so! Voyager 2 managed the same feat in 2018.
Holst’s Planets — both the orchestral suite and the Planetarium Sounds show — cover the worlds of our Solar System. But the ethereal, haunting sound of Holst’s Neptune hints at what lies beyond the most distant planet of our Solar System. Likewise, during the show I can zoom far out from our Sun and offer the audience a glimpse of the galaxy of which our Solar System is only a tiny part — the Milky Way.
Both Alan Leo and Gustav Holst knew that the Universe is a huge place, full of many wonders. Eventually I’ll be able to share these wonders with you in the Planetarium again, and I can’t wait.
