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A tail of copper

Two views of the same meteor
RELATED TOPICS: METEOR SHOWER
OMearaStephen
On August 13, 2015, Astronomy Senior Editor Michael E. Bakich shared the experience of watching the Perseid meteor shower with his wife, Holley. Around 4h UT, they saw a magnitude –8 fireball that boasted a brilliant, 35°-long path.

“The coolest thing about it was the color,” Bakich blogged on Astronomy.com. “It started as a classic lemon yellow, but the last 10° of its run took on a distinct coppery hue.” Bakich wondered if this was a “true shift in the meteor’s color or if the red and green cone cells in his eyes were fatigued with an overload of yellow.”
Image1
The streaks on this page show the perceived colors of a meteor seen by Michael and Holley Bakich, who were observing north of Milwaukee, Wisconsin, and Deborah Carter and the author, observing in Maun, Botswana. The author asked Michael Bakich and Carter to select the color of the meteor trail from a color chart. The choices show a slight difference.
All images: Stephen James O’Meara
Curiouser and curiouser
When we focus on a color for an extended time or if the source of color is exceedingly bright, our eyes’ color-sensitive cone cells can become desensitized (fatigued), leading to an optical illusion called an afterimage — a lingering pseudo-image of the source but of the opposite color. Because the complement of yellow is blue, the copper color Bakich and his wife saw was not an afterimage.

However, an afterimage projected onto the color that stimulated it can alter the original color — a phenomenon known as successive contrast. As color-theory expert David Briggs of the National Art School in Sydney, Australia, explains, “Successive contrast resulting from adaptation is the actual explanation of the phenomenon sometimes mis-labeled ‘fatigue’ of the eye.”

When a blue afterimage is superimposed on yellow, the yellow turns … copper! Is this the end of the story?
Image2
When both choices appear against a similar dark background, however, they look even more like each other. These observations of the same meteor, taken some 8,200 miles (13,200 kilometers) apart, were a spectacular coincidence.
Shared experience
Around 4h UT on August 13, Deborah Carter and I saw a similarly long and bright Perseid fireball from Maun, Botswana — and the meteor was copper colored! The principal difference is that we saw the fireball against the bright blue of dawn, so contrast effects did not affect our cone cells as strongly. That’s why high beams from a car do not overpower the eyes as much in the dawn as they do at night.

Curious, I asked Bakich and Carter to select from the same color chart the shade of copper they saw; I independently did the same. The results, shown here, are amazing. Carter chose a slightly redder shade of copper than Bakich, but that difference disappears when seen against a dark background.
Image3
Adding the author’s color selection shows that he saw a slightly redder trail, but he was looking away from the meteor toward a brighter part of the sky, so a contrast effect may explain the difference.
I selected a slightly darker shade than Carter, but I was also looking away from the fireball when it appeared, concentrating on a much brighter part of the sky, so a successive contrast effect may have had a role in my observation. Still, when I compared all three observations against the same dark background, any color difference is slight. Was the copper color a true color shift?

According to the American Meteor Society, “The dominant composition of a meteoroid can play an important part in the observed colors of a fireball, with certain elements displaying signature colors when vaporized.” Iron, one of the most common elements found in meteors, glows yellow to yellow brown, while sodium produces an orange-yellow hue, similar to the colors we observed.

A rip in heaven
One final note: Carter did see an additional afterimage effect. As the meteor moved across the sky, she saw it tear open a rift in the meteor’s wake, as if allowing her to see the darkness of space beyond. The rift was the lingering dark-blue afterimage of the copper meteor streak, which remained visible briefly against the dawn’s light as the fireball moved rapidly across the sky. As always, send your meteor observations and any thoughts to sjomeara31@gmail.com.
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