the painting that launched a thousand careers

"How did you get into astronomy?" is a question that you tend to get asked a lot when you do what I do. I'm not one of those people who can tell you that I looked through a telescope at Jupiter when I was 5 and decided there and then I wanted to do astronomy and only astronomy. I have always been interested in astronomy, for sure. But not exclusively! Along the way I wanted to be a writer, a teacher, a historian, a paleontologist (dinosaurs!!)… even an actor, briefly (I really sucked at it). My parents were pretty awesome and always encouraged curiosity in whatever I did - one of my favourite book series as a kid was the "I Wonder Why" series, they're still around!

But! I do in fact remember looking at a book when I was little, and it did happen to be an astronomy book. It was about the Solar System, and it had an artist's impression of Saturn viewed from one of its moons. Saturn was on its side as viewed from this moon, and unlike our Moon or the Sun, filled most of the horizon sky in that direction. It was amazing! I thought then, wouldn't it be so absolutely fantastic to stand on that moon, looking up into the sky and seeing the gigantic bulge of Saturn taking up so much of it? It would be surreal.

Thanks to the wonders of modern technology, you can now check out what the various Solar System planets would look like viewed from Earth, if they were at the same distance as the Moon. Check out the sexiness of Saturn! Actually, all the planets look pretty cool. But I also read the text of the article, and I laughed a bit at this section:

"Of course," he continues, "the role of being an inspiration is important, too. Space artists have in fact been an important factor in the history of the development of space flight and have additionally inspired hundreds of people to pursue careers in astronomy or astronautics." He points to a painting by Chesley Bonestell from 1944 of Saturn as it would appear from its moon, Titan, once described as "the painting that launched a thousand careers."

Looks like I'm not the only one intrigued by such imagery of Saturn! I looked up which painting this was talking about, and found a page with that same quote on it (must be pretty famous). Looks like this is the painting the quote is talking about:

But the one closer to what I saw as a kid (and it wasn't this one) was the view from a different moon, Mimas, as imagined by Bonestell:

I was relieved to see these paintings labelled, because at first I thought the Mimas painting was supposed to be the view from Titan and didn't think Titan was orbiting anywhere near that close to Saturn to have such a view. But Bonestell was not your average space artist, it seems, and I think he got the relative sizes quite accurate.

But did he? Let's find out!

Data
We need some basic data about Saturn, Titan and Mimas first.

Saturn's diameter (no rings): about 120,000 km
Saturn's diameter (with rings): about 280,000 km
Saturn-Titan average distance: about 1.2 million km (!)
Saturn-Mimas average distance: about 185,000 km

The size of Saturn, and its distance from each moon, determines how big it will appear on the sky. This is called the angular size of Saturn.

A bit of math
Here enters a little bit of math. Trigonometry, to be specific! Have a look at this schematic:

The purple triangle on the left uses the small angle approximation, which basically means that for small angles, sin(x) is roughly the same as x. But the "proper" way of doing the trigonometry is shown on the right. Not convinced they are the same? This is the difference between the two for the angular diameter of Saturn (no rings) as viewed from Titan, courtesy of my lovely friend WolframAlpha:

Results

In tabulated form:

Saturn (no rings) Saturn (with rings)
Titan 13º
Mimas 37º 87º

Without even going into any more detail, we can already conclude that Saturn is really big in the sky for both these moons. For comparison, our Moon is about 0.5º in Earth's sky. So just the body of Saturn is already 12x the Moon's diameter from Titan and 74x the Moon's diameter from Mimas!

How good was Bonestell?
Pretty darn good in my opinion. It's a bit tricky to judge his paintings and their scale because we don't really know how big the land features are, or how far away they are meant to be. But the relative scale of Saturn in Titan's sky is pretty good, since it's bigger than our Moon but not ridiculously big. Same with Mimas, it takes up a much larger fraction of the sky as it should given that 37º is a huge chunk of the view of a horizon.

But we can do better than just agree that he was pretty good. I hadn't used it before tonight, but Stellarium is some amazing free software available cross-platform - easy to use, and so powerful! You can view the sky not just from Earth but from various moons and planets of the Solar System. Too awesome. And perfect for checking this out further. I changed the location to Titan and Mimas respectively, and played around with the position on each moon as well as the date (which affects how the sky and Saturn appear).

Here are the results for Titan, shown next to Bonestell's 1944 imagining:

And the results for Mimas, again next to Bonestell's visualisation:

Not bad, eh? I'm seriously impressed by the accuracy of an artist who lived in a time before space travel and probe exploration! Before we got the first images of the planets from space. If you handed me a piece of paper and said "draw the view of Saturn from Mimas", even with the distance data included, I doubt I'd get anywhere near as close as Bonestell did. Wikipedia tells me that the fog on Titan might ruin any chance of seeing the planet so clearly as in Bonestell's art, but this is a fairly minor criticism.

So there you go! Chesley Bonestell was a pretty amazing artist, and I think must have been someone who paid a lot of attention to detail. Wernher von Braun (one of the founders of modern rocketry) seems to have also noticed this characteristic:

Wernher von Braun, the German rocketry genius and chief architect of the massive Saturn V booster that catapulted men to the moon, wrote about Bonestell: "My file cabinet is filled with sketches of rocket ships I had prepared to help him in his artwork — only to have them returned to me with penetrating detailed questions or blistering criticism of some inconsistency or oversight."

Incidentally, I also found a really nice painting much closer to what I saw in that picture book all those years ago, by John E. Kaufman:

I don't think I have a 'career' yet, and I think it's an oversimplification to say that a single painting is capable of launching a thousand careers. There were lots of important steps on my path to astronomy: my parents, the telescope I got for my 10th birthday, my high school physics teacher, one of my first university supervisors… not just a painting!

That said, the work that space artists has the power to amaze and inspire, and definitely (even now) plays a critical role in bringing the research that astronomers do on other worlds, faraway stars and distant galaxies to life in a way that words and plots never can.

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