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.
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