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Astro Bob: From auroras to prismatic grass, light touches us all

I thought last night's aurora was spectacular. Then I woke up to my lawn.

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After the aurora, many of us awoke Thursday, Nov. 4, 2021, to frost-covered lawns. I deliberately threw this image out of focus to better see the intense colors in the grass from sunlight refracted by billions of minute ice crystals. Contributed / Bob King
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Are you still rubbing the sleep from your eyes? Let me guess. You were up late watching last night's northern lights show. At least I hope so. After watching some great action around 11 p.m. I went to bed at 1. Too early apparently. The display peaked around 2 a.m. and then again around 4. I laid my head on the pillow suspecting that this would happen, but for once, I needed sleep.

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Striking rays of northern lights stretch upwards into the northern sky Wednesday night, Nov. 3, 2021, around 11:10 p.m. CDT. Both the green and red colors are caused by oxygen atoms excited by the influx of solar ions during the auroral storm. Contributed / Bob King

Although space weather forecasters predicated a moderate G2 event, it evolved into a full-blown G3 geomagnetic storm with aurora spotted as far south as California. Once again, coronal mass ejections — blasts of solar particles from our increasingly active sun — stoked the cold flames of green light. Good news. There's a fair chance we'll see more aurora tonight (Nov. 4), although on a smaller scale. Be on the lookout from nightfall till midnight .

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In this fisheye view from Wednesday night, Nov. 3, 2021, the aurora and Milky Way, top, make opposing bows. The red glow is a faint auroral band that appeared colorless to the naked eye. Contributed / Bob King

After getting dressed this morning, I looked out the window to an equally amazing sight. The cold, clear night spangled the grass with a thick frosting of ice crystals. From my vantage point the sun shone through the frozen gems, which refracted its light into vivid prismatic colors. Tilting my head this way and that the colors shifted and sparkled like rainbow glitter.

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This ground view shows frosty blades of grass and the prismatic colors created by the ice crystals that coat them. Contributed / Bob King

I couldn't wait to get a close-up look at the tiny grains responsible for the incredible sight. I quickly found my camera and was soon slinking around the grass like a ferret. Ice crystals, just like lenses and prisms, have the ability to bend light and spread it into its component colors like a turkey fanning its tail.

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Ice crystals can act like prisms and bend (diffract) white light into every color of the rainbow. Contributed / Wikimedia Commons

This spreading of light is called dispersion, where each color is bent by a different amount and becomes separated from its kin. The same thing happens inside countless, falling water droplets to create the familiar summertime rainbow.

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Up close we can see the simple complexity of built-up ice crystals (frost) on a single blade of grass. Contributed / Bob King

Through the lens I could make out hundreds of tubular crystals comprised of thin, stacked hexagons. Like a stone mason erecting a brick wall, molecules of water in the air fit themselves into place overnight to create these miniature fortresses. No hand was needed. Simple physics based on the atomic structure of H 2O set them in place. The result? Glints of intense color that can make our hearts soar.

As I write, the show is over. Sunshine has warmed the air and melted the ice. The lawn is wet and will soon be dry. But just like the aurora, the morning glitter will return again when conditions are right.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob .

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune.
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