Blog #4 - Reading Summary - Seeing

Seeing 

Despite the advanced technologies of telescopes in their ability to improve resolution and focal length through improving optics, there are still some factors for telescopic observation that are out of humankind's hands. One of these important factors is known simply as seeing. Seeing is the ability to get a clear image through the natural distortion caused by changes in density and temperature in Earth's atmosphere. Changes from the centimeter to meter scale can cause significant decreases to an image's resolution. Seeing is actually what causes stars to "twinkle" when the light from a point source star is diffracted through the atmosphere.

I found it particularly interesting that seeing is the main reason that many observatories are located where they are. I have always heard that remote places like Hawaii and Chile have "better" night skies but did not realize that these locations have less dense atmospheres and less variable atmospheric temperatures giving the incoming light waves less distortion on their way to large optical telescopes.

In fact, the best location for seeing is out of the atmosphere all together! The telescope currently with the least diffraction is the Hubble Space Telescope located 380 miles above the surface of the earth. At this location there is nearly 0 diffraction limitations and only manmade errors in the grinding of telescope mirrors cause obscuration of the incoming light from galaxies, stars, planets, and other celestial bodies. According to calculations in the book, the resolution of the Hubble Space Telescope is .0127'' or enough to see a quarter from over 400km, a true mind bending thought.