31 October 2014

Amazing Sunset and Sunrise Colors

Every sunrise and sunset provides a wide range of visual effects, ranging from the elongation of the disk of the Sun as it hugs the horizon, to the amazing range of colors you see in the minutes before and after the Sun’s passage through the horizon. One of my favorite effects is the curious coloration of the opposite horizon from the sunrise or sunset where one sees a colorful and rapidly changing band of sky called the Belt of Venus.

Belt of Venus at 35,000 Feet
Despite the name, the effect does not have anything to do with Venus the planet. Rather, the effect is due entirely to the shadow cast by the Earth into space, and our perception of that shadow as we observe the horizon from our vantage point along the Earth’s terminator. As we gradually rotate out of the darkness of night (at sunrise) or into the darkness (at sunset), we have a short-term view into the shadow of Earth which occupies the opposite horizon from the Sun. The colors are quite vivid with dark blue low along the horizon, and the refracted colors of the sunrise or sunset above that, creating a layered effect of blue and pink.

Belt of Venus on SF Bay
The images to the left and right show two interesting views I had of the Belt of Venus over the past many months. The first one was taken from 35,000 feet above the United States where I had the very unique vantage point of looking sideways into the sunset belt from high altitude rather than seeing it from sea level. I still cannot figure out why there is a white glow below the belt itself. The second image was taken from the Exploratorium in San Francisco, looking east after sunset toward Treasure Island and the Bay Bridge. The colors and pattern on the horizon were to be expected, but the rays of dark and light blue extending up into the sky were not. Here in this situation, I still cannot figure out the atmospheric phenomenon that would cause such an unusual ray of dark blue to extend upward into the sky. But in both cases the interplay of color and light was indeed remarkable and although pictures from an iPhone camera cannot do justice to the magnificence of the real thing, it’s something I felt compelled to document and write about.

So next time you are watching an amazing sunrise or sunset, be sure to turn around and take in the drama on the other horizon, or you will have missed out on some of the most beautiful parts of the sky.


Paulie said...

Thanks for sharing those gorgeous photos of the Belt of Venus from 35,000 feet, and the sunset glow. I have also seen and photographed light and dark rays like that after sunset. I suspect they are crepuscular rays, but I do not know for sure, or what the true cause might be if not. They're always beautiful, nonetheless.

The Urban Astronomer said...

Hey Paulie - good comment. I just did a quick bit of research and in fact the rays on the image of the Bay Bridge are anticrepuscular rays, since I observed them in the opposite direction of the Sun. http://en.wikipedia.org/wiki/Anticrepuscular_rays

Nice to learn something new today! Thanks for sharing.

-- Paul

Paulie said...

Very cool! I will have to look for those sometime.