What we “see”

by S. Prasad Ganti

We heard in the last couple of lectures how the data from the James Webb telescope is processed by visual specialists using tools like specialized algorithms and Photoshop to come up with the stunning images of the universe. A grand intersection of science and art. The fact that so much processing is done before the images are produced is due to what our eyes are geared to see. To overcome the limitations of human sight. 

That brings us to the question of what is sight, what does it mean to “see” ? At a high level, light emitted by an object or light reflected off an object is received by our eyes and the image of the object is perceived by our brain. Light is a small part of the spectrum of electromagnetic waves. The spectrum comprises radio waves, microwaves, infrared waves, light, ultraviolet waves, x-rays and gamma rays. Radio waves oscillate at the lowest frequencies while gamma rays do so at the  highest frequencies. Different colors represent different frequencies of oscillation. Other than light, the rest of the spectrum is invisible to human eyes. In fact it is a boon to mankind that we cannot see other forms of radiation. Else, the radio waves all around us going from our cell phones to the cell towers would block our vision and we would not be able to “see” beyond a few feet due to the ambient haze.        

All bodies in our universe emit radiation. The type of radiation depends on two factors. One factor is how hot the body is. Hot bodies like the Sun emit visible light, largely yellow. Hotter bodies than the Sun emit blue light. Colder bodies than the Sun emit red light. Still colder bodies like Earth emit infrared light. Infrared light is basically heat, which we feel but cannot see unless we wear the special night vision glasses.

Second factor which governs the type of radiation is if the body is moving away from us or towards us and at what speed. Our universe is expanding, which means the galaxies are moving away from each other very rapidly. Due to “Doppler effect”, the radiation from receding objects drops in frequency. The waves get stretched or are  “red shifted”. Faster the object is receding from us, the more red shifted it is. As Edwin Hubble discovered, the further an object is, the faster it is moving from us.  Most of the light from distant objects is so red shifted that it falls in the infrared region by the time it reaches us. The James Webb space telescope operates in the infrared region – both near and mid, as opposed to the Hubble space telescope which is visible plus near infrared region. Due to this factor and the bigger size of the mirror, James Webb can see farther than Hubble. Seeing further means looking backwards in time.      

Now back to the eyes. Ants can see ultraviolet light.Some birds, fish and reptiles can detect ultraviolet light. There are some photo receptors in the eyes which consist of proteins called “opsin” which can absorb a photon. There are different types of such pigments. Humans are trichromatic meaning that they can see three colors – red, blue and green. Every other color is synthesized from these three colors. Birds are quadchromatic, which means they can see four colors as primary colors. That could be the reason some birds can see ultraviolet light.  Also, in human beings, our lenses block out the ultraviolet light. It is reported that  the French painter Claude Monet lost his eye lens at the age of 82. He then started seeing ultraviolet light. It is supposed to be perceived as whitish blue. His later paintings of water lilies show this kind of a hue.

Another feature of the distant objects is that the  radiation from them is very feeble, having traveled millions and billions of light years in its journey. More radiation needs to be collected over a period of minutes or hours before any sense can be made out. Eyes are very poor at staring at some object for a longer time to collect enough light to form a sensible image. Cameras contained within the James Webb telescope can collect and tabulate the data received. 

The collected data is manipulated so that it is shifted to the visible spectrum to show colors which humans can perceive. What is the utility of “photoshopping” such data to produce artistic images ? Because the basic data collected is good for doing research and drawing conclusions. My 2 cents is that the artistic touch is for the purposes of public outreach. When billions of government dollars are spent on complex scientific instruments, we cannot just throw a table of numbers or a graph to educate the taxpayers. Besides, scientists who spend most of their lifetimes on such missions need some visuals to feel good about. Increasing sophistication of each generation of such images represents the progress being made in development of more complex scientific  instruments. 

At some point in the future, when the universe might stop expanding, we might see light from distant objects without any manipulation ! But Earth-like planets will still emit feeble infrared radiation. 

This entry was posted in April 2023, Sidereal Times and tagged , . Bookmark the permalink.

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