The Sun
The McMath-Pierce Solar Telescope at Kitt Peak

As the sun nears the horizon it appears to be flattened out.

The sun sets behind mountains as seen from Kitt Peak.

The control room and lab of the McMath-Pierce Solar Telescope where the above images were taken, and an outside view.

The setting sun reflects off of the table top projection from the McMath Solar Telescope.  From left to right:  Dr. T.A. Clark, John and Diane Smith and Alex Mandel.

These images were taken by pointing my Nikon D100 with a 35mm f/2.8 Nikor lens down at a table top on which the McMath-Pierce Solar Telescope had projected an image about 2' across.  The telescope is able to track the sun all the way down to the horizon.  

The reason gets redder as it begins sun begins to set, is that the light must travel farther through the atmosphere before it gets to the observer.  The shorter wavelengths of light, especially blues, are scattered in the atmosphere. Only the longer wavelengths, red and oranges, are left in the direct beam that reaches your eyes.  The lower the sun the greater this effect.  The narrow band of green at the top of the sun is what is not fully scattered of  the shorter wavelengths.  This effect is always present near sunset but is only visible to the naked eye when atmospheric conditions are right and the sun actually has dipped below the horizon, and is then known as the "green flash."

My sincere thanks to Dr. T.A. Clark, Professor, Department of Physics, University of Calgary, for letting me observe and photograph the setting of the sun through the McMath-Pierce Solar Telescope.