What You See Ain't Exactly What You Get
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One of the most disappointing times for a newbie backyard astronomer comes when he or she looks for the first time through a brand new telescope and sees pretty much nothing. Well, nothing like what one sees on the covers of Sky and Telescope or Astronomy magazine or on websites like Astronomy Picture of the Day.
All those amazing images that have been pouring into the public mainstream for decades - grand and colorful spiral galaxies, kaleidoscopic nebulae, far-flung remnants of supernovae - are seemingly nowhere to be found.
Why is that, though? Why is it that when one looks, for example, in the astronomy journals at images of our sister galaxy, Andromeda, that the rich detailed blue spiral arms and central yellow fireworks come to life, but using our own eyes through even a good amateur telescope we see nothing much more than a grayish-green faint celestial fuzzball?
It’s a question of design and engineering.
Our eyes have been designed for life on a sunny planet. They are amazing works of art, able to capture photons of energy and translate them into electrical messages for the brain where those messages are turned into images.
But our eyeballs are inefficient in the best way. They are actually able to capture and process less than one in a thousand photons that make it in. Which is great, if you think about it.
If our eyes could suddenly process more photons, like one of a hundred or one of ten, all around us would seem intensely bright. We’d need some sort of filters to reduce the photon count.
Not capturing a lot of photons is not the only “problem.” Our eyes also don’t store photons to make the images we see.
Say some lucky photons enter the eye and react with the chemicals in the retina, the layer at the back of our eyes. These chemicals send their message to the brain but then “reset” for the next photon strikes.
This resetting allows continuous and successive images to be made and translated quickly so we can get constant and accurate updates from the outside world. Without this chemical process the entire world would seem more of a blur than it is already.
Try staring at something for a minute. Then close your eyes and see the image still there quickly fading away. Those chemicals are resetting; the image is soon gone.
Those beautiful space images we see are processed differently. Nowadays nearly all telescopes have charged couple devices (CCD) hooked up to them that act sort of like an artificial retina for astronomers. But these “retinas” work a little differently than human retinas.
First, they can capture and use more than half the photons that strike them! That is great efficiency.
Moreover, in CCDs the energy from the incoming photons can be stored. Heavenly objects appear very dim and fuzzy to our eyes because we can’t get enough photons to make a discernible image. But in one of these fancy cameras the energy from photons can build up over time until an image can finally be seen.
Some of the great images we have now are a result of minutes to hours of exposure to a single heavenly object. Some of the Hubble images of the faintest, most distant galaxies out there required over 30 hours of exposure! We’d never see those staring through a telescope ourselves.
And of course the images nowadays can be digitally manipulated to bring out colors and different textures and hues, things we are unable to do with our eyes.
On top of that some telescopes can “see” in wavelengths we cannot, such as infrared, ultraviolet, and X-ray.
Modern technology has allowed us to see incredible wonders of the skies in breathless detail, to be sure. But it doesn’t beat a walk out on a clear moonless night where most of us can - with our very own eyes - observe and absorb the awesome glories of the starry heavens.
Posted by Mark Ritter at 2005.01.29 09:30 PM | Comments (0)
