"Looks like the mystery is solved," adds Chester. "Although technically the trail is closed dusk to dawn, I know of many folks who use it as a bike commuter route after dark, especially this time of year. The beads enhance visibility. I got plenty of strange looks from passersby as I was taking the pictures!" www.spaceweather.com
Usually rainbows are seen near storm clouds. A few days ago, Geoff Chester was riding his bike in Arlington, Virginia, when he looked down and found one in the asphalt. "Here's a picture from my cellphone camera," says Chester. "You can see the rainbow arc to the right." According to atmospheric optics expert, this is not a rainbow, but rather a glass bead bow. He explains: "Crews marking paint lines on roads often scatter small glass beads onto the paint. The glass beads retro-reflect light and this enhances the visibility of the markings at night. The glass beads - if sufficiently spherical - also produce rainbows. The difference is that the refractive index of glass is greater than that of water and the bow is only about 21° in radius compared to the rainbow's 42°. The glow around the shadow of Geoff's head is an antisolar point phenomenon - a heigenschein - produced by refraction through the glass spheres."
"Looks like the mystery is solved," adds Chester. "Although technically the trail is closed dusk to dawn, I know of many folks who use it as a bike commuter route after dark, especially this time of year. The beads enhance visibility. I got plenty of strange looks from passersby as I was taking the pictures!" www.spaceweather.com
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Image credit and copyright: David Hathaway/NASA/MSFC The apparition might be connected to hurricane Sandy. The core of the storm swept well north of Alabama, but Sandy's outer bands did pass over the area, apparently leaving behind a thin haze of ice crystals in cirrus clouds. Sunlight shining through the crystals produced an unusually rich variety of ice halos. "By my count, there are two sun dogs, a 22o halo, a parahelic circle, an upper tangent arc, and a parry arc," says Chris Brightwell, who also photographed the display. "It was amazing." If the display really was a result of Sandy, sky watchers might not have to wait a decade for the next show. Some researchers believe that superstorms will become more common in the years ahead as a result of climate change, creating new things both terrible and beautiful to see overhead. Sky watchers in the storm zone should remain alert for the unusual. GROUND-HUGGING RAINBOW: Most rainbows arch up into the sky, but on Oct. 27th, Stefan Elieff of Punta Arenas, Chile, photographed one that seemed to hug the ground: "Scattered rain clouds were rolling in low over the hills behind the city when this unusually low rainbow appeared," says Elieff.
Although low rainbows are seldom seen, they are actually quite common. They appear whenever raindrops are illuminated by a high-hanging sun. "A rainbow's center and the sun are always on opposite sides of the sky," explains atmospheric optics expert Les Cowley. "So when the sun is high, the rainbow is low. Indeed, as the sun climbs, the rainbow sinks--sometimes right into the sea." www.spaceweather.com |
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