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Today in science: A spacecraft obliterated a sundog

On February 11, 2010, as NASA’s Solar Dynamics Observatory (SDO) was launched into space, its path took it directly through an atmospheric optical phenomenon known as a sundog. 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. 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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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.

Diagram of sun with halos and enlarged, labeled ice crystals.
In this simulation, the sun is surrounded by a 22-degree halo and flanked by sundogs. Read more at Les Cowley’s Atmospheric Optics.

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.

Distant glowing rocket exhaust surrounded by thin circular lines in the clouds.
View larger. | When the Solar Dynamic Observatory (bright streak in lower left quadrant of photo) lifted off from Cape Canaveral on February 11, 2010, its launch enabled optics experts to discover a new form of ice halo. Image via NASA/ Goddard/ Anne Koslosky.

Cowley and colleague Robert Greenler at first couldn’t explain this column of light. Then they realized that the plate-shaped ice crystals were organized by the shock wave from the Atlas V. 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.

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By the way, NASA’s Solar Dynamics Observatory has now been observing the sun for 11 years. It’s one 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 launched into space ripped apart a sundog and created a new ice halo that amazed scientists.

Via Science@NASA

Via Les Cowley’s Atmospheric Optics

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February 11, 2021

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