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It’s what you can’t see that counts
It’s what you can’t see that counts
By Tom Benjamin
This article is about a most important but overlooked instrument in astronomy: perspective. We use perspective all the time. Our binocular vision is an example. The two eyes give us 3D imaging. The movement of our eyes also contributes. It is the change that gives us ‘perspective’.
I referred to this in my previous Cloudy Nights article “The Best Views of the Universe are From our own Backyards”. In that article I mentioned that we needed to view things through different angles, distances and modalities to understand their nature.
Astronomical objects can’t be perceived in 3 Dimensions with our eyes because they are too far away. However in the 20th century we have available tools that can give us perspective: -ie- the automobile and airplane. Moving significant Earth distances allows just enough change to give us some cosmic perspective. There are other perspectives available. We can use faintness and tininess to understand brightness and gigantic size.
Using one eye requires movement to get a 3D perspective – our brain does the rest. On the larger scale we use our book knowledge to help our brains flesh out that which can’t be seen directly. If we know the globular cluster we’re looking at is supposed to be a sphere it helps us perceive its shape. This can be a mere illusion as there is no guarantee that what appear to be the foreground stars in the ball are actually such. They might merely be brighter stars further back in the ball! But does it matter? - Only for scientific purposes. For visual purposes such an illusion would only enhance the 3D effect.
Similarly, knowing the shape of a typical barred-spiral galaxy helps us perceive the shape when it’s just a faint smudge in the eyepiece. Book knowledge prepares the brain for what to see. Overly graphic portrayals such as sci-fi epics or animated documentaries can actually impede perception if they presented images so unreal that our brains expect something too different from what we see in the telescope eyepiece.
So books are important astronomical tools and so is the automobile
One evening we realized the power of the automobile for perspective. We were travelling East and going up an extended incline. Orion was rising and the road managed to keep Orion straight ahead of us. Orion spans around 14 degrees which is really only about the size of my hand held up to it. In the car, however, this loomed much larger because trees blocked out the sky above the sides of the road, effectively giving Orion domination of our view through the car windshield. What made particular impact was the effect of ‘driving to Orion’. Once this had gone on for many minutes, the clear impression was that it was not moving at all. It was the backdrop to everything. Other very large objects passed by at their usual rate – clouds, trees, towns … but we easily got the feeling that we could drive forever and never get to Orion. It would always be at the same distance. With the M42 Nebula 1400 light years away, ‘forever’ would be no exaggeration for a car trip. Suddenly the vast size of the constellation hits us – far bigger than anything we could experience.
Yet from my Sydney balcony it just looks like a handful of lights in the sky. It took the automobile to get the perspective. And the automobile is a fairly recent invention. Most Earth people do not have one.
The Milky Way is even more of a perceptual challenge. It surrounds us. It’s hard to connect the ‘summer Milky Way’ and the ‘winter Milky Way’. Again, the astronomical perspective used is a vehicle – the airplane. If I fly to a really remote area (the sort of place where there are no radio stations), civilization gets smaller and fainter and the Milky Way gets that much brighter and its extent gets wider. And this is the perceptual impact. Having come this far you realize that if all were stripped away – the trees, the clouds, the very ground beneath – the Milky Way would still be there – and brighter! And it would be around us in all directions, unchanging. The Milky way is the backdrop to everything. Our mind would see the foreground stars as merging away into its vastness. But it is only the travel that has made this perspective possible. I’m not likely to get any such sensation from the faint glow visible from my city balcony.
How can we use faintness to let us see brightness?
Well, the problem is that galaxies are huge yet faint. However far I travel from the city, the Milky Way is no match for moonlit clouds. Yet it is that very faintness that makes it impressive. Once you understand that the Sun and foreground stars are merging off into its clouds you can gauge just how far away the centre must be, hence how vast its entirety. And the faintness speaks to its sparseness. Galaxies are not dense clouds as seen in time exposures and animations. They are sparse fogs. Their density is less than any vacuum we create on Earth. It is only because each point is a nuclear furnace that we can see them at all. Neighbour galaxy M33 is a face-on neighbour with a span like part of the Moon but it’s a mere feeble glow, visible only with optical aid. Even the nearby Clouds of Magellan which span larger than the moon look like a fog.
Ancient civilizations could not know the scale or significance of the Milky Way. It was not until after the 1500s that anyone proposed that it included the foreground stars but the ancients at least knew it was a central part of the fundamental backdrop to their world. They couldn’t miss it. It was there every dark night.
The best way to see the Milky Way with my eyes is to focus on the dark lanes. This allows peripheral vision to pick up the shape from the glowing bits at the sides. Even then, it’s only because I’ve seen wide-field time exposure photos over the years (i.e., in good old-fashioned books) that my brain can make out its familiar shape.
Only recently have astronomers perceived the Andromeda Galaxy and M33 as its companions. The fact that these are so faint and small makes them all the more impressive. Once one has comprehended the vast sparse Milky Way one can appreciate that these are indeed neighbours. They are like the Milky Way but in space being neighbourly means very, very, very far away.
Another perspective vehicle is the satellite. I’m not talking about being aboard it. Rather, I’m talking about following one with binoculars or telescope as it flies through our field of view against the black backdrop of stars. Again it is what is not moving that is significant. Sci-fi movies often portray stars as moving past the spacecraft porthole like clouds past an airplane window. They get away with this artistic license by positing ‘warp speed’ and other sci-fi. Watching a real satellite against a real night sky clearly shows the stars as a vast backdrop. We know that the satellite is moving quickly. We can see that it rides higher than a plane. Because of the 2-dimensional appearance of the stars we can see that they are a backdrop and that the satellite is a speck moving against this infinite backdrop rather than through it. Indeed, it takes some shift of consciousness to break away from the sci-fi images of rockets moving amongst the stars. But that is the point – to see what things actually look like in space.
We can use the moon and planets for perspective
Again, I’m talking not of visiting planets but of observing them from Earth. Planetary conjunctions are commonly associated with astrology but they have much to offer as perspectives. When two planets are close enough together to fit in a field of view at 20x or higher it gives us a chance to see them in perspective. If Venus and Jupiter are in the same field it becomes easy to see that Venus is a superbright reflective object and Jupiter is a much-faded but larger object off in the distance. Knowing their relative sizes aids the effect. A bit of thought tells us that Jupiter is probably on the other side of the Sun to our position, given that it is in the same field as Venus, which travels in an inner orbit. So we can see that one is a giant object far way from Earth and Sun and the other a smaller near neighbour. Combinations of Mercury, Venus, Mars, Saturn, and Jupiter can all show these effects. Even with the naked eye we can see the difference in their radiance. When similar in magnitude, Jupiter has a much more pale hue than Venus.
Colours through a telescope thus give us perspective. Jupiter in a large (14 inch+) telescope shows the same colours as an Earth sunset. Some amateur photos on YouTube capture this well, whereas some false-colour enhanced Hubble and Voyager photos mislead our brains. A true-colour image immediately helps our perspective because we’ve seen so many Earth sunsets. Our brain can instantly recognise these as cloud colours faded because of the great distance from the Sun. This familiarity helps us get the ‘feel’ of Jupiter as a distant cloud ball. Venus is more like clouds in bright sunlight, still a familiar Earth sight. The other gas planets are more of a perceptual challenge because their yellow, green and blue colours aren’t common to much on Earth.
The brightest object of all ought to help us understand stars and galaxies, yet it is very difficult to comprehend that the Sun is a star. A few of the ancient Greeks proposed the notion but it was not taken up again until the 1600-1800 era. It is not obvious to the eye, if not least because the Sun blocks out the stars! Nor is it obvious that the stars are at differing distances from us or that they merge into the clouds of the Milky Way. All this we take for granted only thanks to the efforts of generations of star gazers who have put this into books.
Not everyone has books. There would be many on Earth who know little of any of this. World literacy is now as high as 84% but this refers to basic reading. Astronomical literacy is a refinement built on top of basic literacy. Having known university post-graduates who didn’t know why the moon had phases or the difference between a planet and a galaxy I suspect Astronomical literacy to be much lower. TV documentaries give a sketchy and always confused picture by conflating interstellar cosmology with local so-called ‘space travel’ as though astronauts hovering above Earth were on their way to the stars. This was the stuff of 50s sci-fi, not space-age reality. We haven’t even made it back to the Moon and I no longer want to be a Space Cadet.
So space travel helps very little with seeing the cosmos. But book knowledge of the cosmos is also limiting. When we read about galaxies our mind travels but that is very different from seeing them, let alone perceiving them for what they are. The artificial imagination offered by software may also work against direct perception of the cosmos.
So is astronomical literacy of any significance in daily life?
This is no trivial issue. People still attribute to the sins of some folk calamities that others regard as natural events. Understanding the scale of the cosmos and the forces of nature has constantly changed human perspective. For example, no modern religions regard lightning as bolts hurled by gods. They don’t pray to river gods. Since the Atomic Age we’ve come to realize that even cataclysmic events that wipe out much of Earth life can be caused by a ‘mere’ 10 kilometre rock crashing into Earth. We also know that this was once a common event, indeed the very method of the Earth’s formation.
Such knowledge changes our world views. Modern societies become less likely to see even large events such as earthquakes and hurricanes as much more than natural, explicable events. But traditional societies, even today, look for a human, sorcery or godly intention in every occurrence. A true traditionalist like an Inquisitor can be trained to a high level in understanding modern theories but still asks: “Ah, but which jealous neighbour sent the germs to inflict him?” “Who caused the tornado to hit this particular town?”
Thus there have always been political implications. Even as recently as World War II German scientists were employed to prove the ‘cosmic truth’ of Hörbiger’s World Ice Theory, which viewed the Milky Way as a ring of ice and the stars as ice particles. As with Galileo and Bruno centuries earlier, it was heresy to oppose these views.
At least such debates always led early societies to look for higher levels of abstraction than what was obvious to the senses.
Many intelligent species on our own planet have no hope of cosmic knowledge. Dolphins, however large their brains, are unlikely to make much of stars, if they can even see them at all with eyes built for underwater. So it might be that denizens of planets with many moons, overly bright suns, liquid or cloud covers might never learn of a cosmos. Even educated people in many urban environments see little of the stars and nothing of the Milky Way.
So understanding of the cosmos may well help people to identify their own nature. Sometimes it takes a change in perspective from an ‘event’ to get people to see what they have in common. Catastrophes or positive things like sporting triumphs often bring people together as they are forced to acknowledge their neighbours.
Once early humans learned that the stars, the backdrop to their lives, did actually move, albeit very slowly, it gave them perspective on how vast was their past and future. Having to wait perhaps generations to document the small angular changes in star risings may well have forced a certain amount of patience on humankind. This, in turn, may have had a settling effect as did the time and effort required to build monuments to align with these phenomena.
Modern conceptions of the scale of billions of unreachable galaxies and the complexities such as String Theory proposed to explain our world are bound to have a long term psychological impact. All this will take some time to sink in. In the meantime, why not just help more people start to comprehend our own cosmic neighbourhood?