The air molecules in our atmosphere are more efficient at scattering shorter wavelengths (cooler colors like blues and purple) than longer wavelengths (warm colors, like orange and red). Looking up at the midday sky, we see blue from preferentially scattered blues. The air molecules absorb and reradiate the shorter wavelengths more efficiently than longer wavelengths. When the sun is low in the sky, the light reaching our eye has gone through so much scattering that the bluish colors virtually all scattered from the sun’s rays. The resulting light is orange-red.

When the sun is very low in the sky, at sunrise or sunset, the sunlight is warmer in color due to Rayleigh scattering in the atmosphere.  In this photograph the warm colors are reflected to our eye from the bottoms of clouds and from the snow surface.  As the sun dropped lower this evening the clouds really lit up brightly.  Below the horizon the sun has a longer path through the atmosphere and becomes redder.  If there are some clouds that can be underlit by that red light the sunset sky explodes in color.

The star effect of the sun behind the spruce tree is due to diffraction of light as it passes through the very small aperture in the lens.  Diffraction is the bending of light around an opaque object.  It is a result of the wave nature of light.  The effect is more pronounced when the aperture is very small.

In 2019, a beautiful blue spruce from the Carson National Forest in New Mexico was chosen as the Christmas Tree for the U.S. Capitol.  On this evening as I took this photograph of the sunburst behind this stately tree above Santa Fe it reminded me of a Christmas Tree.  I am hopeful that this tree will see many more sunsets for decades to come as it watches over Santa Fe.