Well today I’m gonna reveal a secret, something you probably didn’t expect and might disappoint you a little. You know all those pretty astronomical pictures you see in Calendar and on web site… Well the object probably don’t look like that, and sometimes not at all. Now, you must understand that the intention is not to deceive but to show the science and what is spectacular about a object and it is also because of the physical limitation we have to work with.
Let me explain, first off let us remember that the eyes is an amazingly complex organ that coupled with our brain can make advanced image manipulation in real time. Also despite of all its power the eye and brain system is still very limited. It can only see in a very tiny part of the electromagnetic spectrum, what we call obviously the visible part of the spectrum.
If you let me go on a tangent here the light our eyes let through is an interesting thing, it is though by many that our eyes see the way it does because we evolved around a G type star that emits most of it’s light in the visible. It stand to reason the argument goes that the most effective way to see is to look into the part where the most light is. However, if you look closely at the light the eyes transmit you find a starting revelation, it is almost exactly the same kind of light transmission than water would transmit. Now, if we think that the eyes is filled with water and that it might have evolved underwater it becomes much more logical don’t you think?
Now knowing that and that we use our telescope not only in the visible part of the electromagnetic spectrum but in every part of the spectrum we can think of a way to detect you might star to see the problem. We have data that our eyes cannot see that we wish to show to our eyes, brining about the concept of false color, i.e when you represent with a color something that is invisible to the eyes. Then there is the fact that the eye is quite wasteful when it comes to light, it doesn’t transmit a lot of the light it receive, which isn’t a problem when you are looking in a brightly lit area like the earth but if you want to look at a faint distant object like a galaxy well losing that light might make the difference between seeing it and not seeing it. To compensate for that astronomer use filters that are design to let in as much light as possible. What does that mean for images? Well it means that some colors have more light then you eyes would sees, making them brighter and more apparent. Now, there is another problem, the fact that eyes always see all the light in the visible, while thanks to our filter we only see a small part of the light. In most case what is done is to take many monochromatic images, i.e. black and white images in a small region of the electromagnetic spectrum. We then gather more of those images (usually around 3, to have a “red”, a “green” and a “blue” image) which we combine using software (like Photoshop).
It is in the combinations process that we try to make the images attractive to the eyes and in most case scientifically relevant. We also correct the images for flaws (for example high-energy cosmic ray, no not the kind that give super powers) and irregularity in the detectors) and then select the colors for each of these images. Sometimes to make the physics of the object more apparent we “cheat” a little with the orders of the colors, we makes things that “should” be green, blue or stuff like that.
But, still despite all this the images are still true to reality, just not the reality our eyes shows us. Astronomers try to make the images beautiful to attract the eyes and make people think about the sky above. Who knows maybe one day someone will come back home from a trip around the Milky way with digital camera pictures of all those nebula and show the world how wrong we where, but until them please enjoy our images, you eyes can see those and they can’t see the object we are showing you.