A rocket obliterates a sundog
On February 11, 2010, as NASA’s Solar Dynamics Observatory (SDO) launched into space, its path took it directly through an atmospheric optical phenomenon known as a sundog. And in the video above, you can hear observers gasp in surprise when the rainbow-hued sundog disappears as the spacecraft passes through that part of the atmosphere. Indeed, it was an auspicious beginning for a spacecraft that has aided in our understanding of our local star. And the launch also brought to light a new form of ice halo and taught those who love and study sky optics new insights into how shock waves interact with clouds.
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What is a sundog?
A sundog is a bright rainbow-colored spot in the sky, formed by refraction of sunlight through plate-shaped ice crystals drifting down from the sky like leaves fluttering from trees. Les Cowley of the website Atmospheric Optics explained what’s happening in the video at a post at Science@NASA:
When the rocket penetrated the cirrus, shock waves rippled through the cloud and destroyed the alignment of the ice crystals. This extinguished the sundog.
A column of light
In the video, keep a close look out for the luminous column of white light that appears next to the Atlas V rocket that powered SDO’s 2011 launch. Although Cowley and other sky optics experts understood why the sundog disappeared, they didn’t understand the events that followed, specifically that white-light column. Cowley said:
A luminous column of white light appeared next to the Atlas V and followed the rocket up into the sky. We’d never seen anything like it.
Cowley and colleague Robert Greenler at first couldn’t explain this column of light. Then they realized that the shock wave from the Atlas V organized the plate-shaped ice crystals. So Cowley explained:
The crystals are tilted between 8 and 12 degrees. Then they gyrate so that the main crystal axis describes a conical motion. Toy tops and gyroscopes do it. The Earth does it once every 26,000 years. The motion is ordered and precise.
Love it!
By the way, NASA’s Solar Dynamics Observatory has now been observing the sun for 13 years. It’s one of multiple observatories that keep an eye on our sun, part of NASA’s Living with a Star program. The video below highlights some of SDO’s achievements over the past decade.
Bottom line: On February 11, 2010, a solar observatory that was launched into space ripped apart a sundog as it passed through clouds, and created a new ice halo that amazed scientists.
Via Les Cowley’s Atmospheric Optics
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