— Paul Cornish, Assistant Planetarium Producer
Of all the the shows on offer by the We the Curious Planetarium, Holst’s Planets 3D is probably the one I’m going to miss presenting the most during our temporary closure. Not only does the show literally allow me to make the heavens dance, but it’s also based around a clash of ideas that I find fascinating. All of the visuals used in the show are based on the very latest astronomical data available, but when Gustav Holst composed The Planets between 1914 and 1916 he was inspired by astrology rather than astronomy.
The show involves a pre-recorded performance by the London Philharmonic Orchestra of Holst’s famous seven-movement orchestral suite. Accompanying the music are specially created 3D visuals of the Solar System created by our Planetarium Developer, Anna Henley using the Planetarium’s Digistar 6 software. A member of our Planetarium Team controls the visuals in a live performance in front of an audience— making the planets, moons, and space probes reflect the music in whatever way we see fit. I’m happy to say that sometimes the person controlling the visuals is me!
Unfortunately I’m not going to be able to present the show again for a while. But one of the advantages of being stuck in the house for the foreseeable future is that I now have the time to do a bit of research on the seemingly conflicting ideas that inspired this show. Are they really so contradictory? Maybe there are parallels to be found between Holst’s beliefs and modern astronomy?
Holst and Astrology
In 1912, while on holiday in Spain, Gustav Holst got into astrology in a big way. For the rest of his life he would cast horoscopes for his friends. He referred to astrology as his “pet vice” and each of the movements of The Planets were based on what astrologers believe to be the influence of each planet on the psyche.
Holst was a big fan of the work of an astrologer named Alan Leo — a man often described as “the father of modern astrology”. Leo is credited as being responsible for moving horoscope analysis towards a more psychologically orientated approach that predicted trends of experience rather than specific events. He made astrology less Nostradamus and more Mystic Meg.
Alan Leo’s ‘The Art of Synthesis’, published in 1912 is said to have been a probable influence on Holst as he composed The Planets. I was excited to find that the entire book is available to read online. It’s fascinating to see the same “personalities” evoked by Holst’s music written down, and even illustrated. But how close to the truth did Leo and Holst come? I decided to compare what we know of each planet in our Solar System today with the ideas laid out in ‘The Art of Synthesis’, and the images conjured by Holst’s music.
“The whole of the purely animal nature in man is under the influence of Mars… In every nativity Mars shows … courage, capacity for heroism, endurance, strength and power.”
“The nature of the planet is positive, hot, and dry…it greatly increases the vitality, energy and activity of the body.”
Alan Leo, 1912
Holst’s Mars is stirring and powerful. It evokes images of heroism and courage, possibly on some fiery and turbulent battlefield. But, like Leo’s writings on the subject, this bears little resemblance to the reality of Mars as we currently understand it. In fact both men managed to evoke images of a world that’s pretty much the complete opposite to the actual Mars.
Leo was way off when he described Mars as “hot”. Mars is sometimes known as “the Red Planet” because of its colour, caused by iron oxide on the surface. But it’s a cold world! On average, the temperature on Mars is about minus 60 degrees Celsius, because its further from the Sun than Earth and has a thin atmosphere which doesn’t hold the heat from the Sun for very long.
It’s far from the turbulent, fiery place conjured up by Leo and Holst. Mars has volcanoes — its home to the tallest volcano in the Solar System, Olympus Mons, which, at 24km, is around three times the height of Mount Everest — but these volcanoes don’t seem to be active. There is some evidence to suggest that Mars may still experience some volcanic activity deep underground, though none has been directly observed on the planet.
Leo was closer to the truth when he described Mars as “dry”. It is indeed dry, and as far as we know, lifeless. Billions of years ago its thought that Mars had lots of liquid water on the surface. Scientists think that asteroids may have struck the ancient oceans of Mars, causing tsunamis that reached up to 300 metres in height. Perhaps the powerful activity attributed to Mars by Leo and Holst did in fact occur, billions of years before either of them were born.
Eventually Mars lost all the liquid water on its surface. Mars lacks a magnetic field to protect it from charged particles emitted by the Sun. These charged particles stripped Mars of most of its atmosphere and there wasn’t enough pressure to keep the water on the ground. Most of it turned to gas and drifted off into space, although some froze as ice at Mars’ polar caps, where it can still be found today.
There is evidence that Mars may have liquid water deep underground. In 2018 equipment on the Mars Express orbiter detected a 20km wide lake, deep under the southern polar ice cap. Unfortunately this sludgy lake is likely to be too salty for life as we know it. During the show I’m able to make the waters of Mars reappear on the planet’s surface, as well as display images captured by the Mars Express probe.
“Venus is the planet of refined taste. It is the planet governing the soul as apart from or opposed to the senses.”
“All things that are sweet and pleasant come under the rule of Venus…It governs all things that are lovely, ideal, and excellent.”
“…its essence is harmony and pure bliss.”
Alan Leo, 1912
Holst’s Venus is calm and beautiful. Like Leo, Holst imagines a sweet and pleasant world. But the real Venus isn’t quite the harmonious, blissed out chill-fest they envisioned.
Even before we discovered what lay beneath the thick, cloudy atmosphere, science fiction writers were predicting a much more hostile world than the one conveyed through Holst’s music. Fiction from the latter half of the 19th Century and the first half of the 20th Century spoke of dense jungles, carnivorous vegetation, dinosaurs, and warrior tribes! It sounds pretty awesome to be honest, but its hardly relaxing.
The reality of Venus is even less blissful! If we suddenly found ourselves trying to walk around on the surface, we wouldn’t encounter any dinosaurs but we would be crushed flat by the atmosphere. It’s 90 times as thick as Earth’s atmosphere!
When the Soviet spacecraft Venera 4 reached Venus in 1964, it revealed that Venus is extremely hot and dry, with clouds of sulphuric acid in its carbon-dioxide atmosphere. Years later, on December 15, 1970, Venera 7 landed on the surface and relayed a steady surface temperature of 475 °C for 23 minutes, before it was crushed by the pressure of the atmosphere and melted by the intense heat.
There is however, still beauty and serenity to be found in the study of Venus, but it takes a bit of imagination. Eight Earth years are roughly equal to thirteen Venus years. This means that if we were to imagine a line stretching from Venus to Earth, the two planets approximately trace out a symmetrical pattern as they orbit the Sun. A similar symmetrical pattern, known as the pentagram of Venus, can also be made by observing the apparent path of Venus from Earth. Using the Planetarium to visualise both of these amazing astronomical patterns is one of my favourite parts of the show.
“Mercury chiefly governs thought for its own sake, especially abstract thought, apart from any practical application. It may give much restlessness and love of change.”
“In the horoscope, Mercury stands for intelligence in all shades and degrees of development, from the merest superficiality and cunning, up to the sublimest genius.”
“…it signifies, thought, understanding, reason, intelligence, intellect…cunning, craft, subtlety, speech and memory.”
Alan Leo, 1912
When Leo spoke of Mercury providing the human psyche with “restlessness and love of change” and Holst composed his playful, flighty, and fast ‘Mercury’ movement, they were both pretty spot on in terms of our modern scientific understanding of the world.
Mercury could indeed be described as a “restless” planet — it makes a complete orbit around the Sun in just 88 Earth days. A year in Earth time is around four years in Mercury time, so on Mercury you could have four birthdays in a year! Your birthday celebrations could last a long time — one day on Mercury (the time it takes for Mercury to complete one rotation) takes 59 Earth days.
Mercury’s not actually that great as a party destination. It’s unlikely life as we know it could survive there, as it’s just as changeable as Leo and Holst imagined, but not quite as subtle. Being the closest planet to the Sun it gets very hot — daytime temperatures can reach a scorching 430 degrees Celsius. However, the thin atmosphere is not enough to retain that heat, and by night the temperature drops to a freezing cold minus 180 degrees Celsius.
The surface of Mercury has also changed a great deal over the years. It’s the most cratered planet in the Solar System as its thin atmosphere is not enough to protect it from asteroids and comets. It’s interesting that Leo associated Mercury with the intellect as most Mercurian craters are named after famous writers and artists. In fact, Holst has a crater named after him!
During 1974 and 1975 Mariner 10 flew by Mercury three times, and mapped just under half of the planet’s surface, and in 2004, Mercury was visited by the Messenger probe. During the show I have the option of switching on a global colour map of Mercury’s surface that was created by mosaicking thousands of images obtained by Messenger’s camera. The colours highlight different points of interest on Mercury. For example, streaks, or rays spreading out from fresh impact craters are shown in light blue or white, reminding us of Mercury’s restless, changeable nature.
So far Holst and Leo’s view of the Solar System is looking pretty far removed from what science has revealed to us. But there’s still four more movements to go. Come back next week as we explore the gas giants — Jupiter, Saturn, Uranus, and Neptune — with Holst and Leo as our guides.