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SOLAR WIND: Earth is entering a solar wind stream. The encounter could cause a geomagnetic storm and auroras over Alaska and Canada. Northern sky watchers, pay attention!
SOLAR ACTIVITY: The sunspot number is zero, but that doesn't mean solar activity is zero. John Stetson of Falmouth, Maine, photographed an enormous prominence erupting on May 17th:
Above: The sun viewed through a Coronado solar telescope.
How big is it? If you placed one end of the glowing filament on Earth, the other end would stretch almost to the Moon. Because of its location near the sun's limb, the eruption did not fling any material toward Earth. That's the best kind of solar activity: Pretty, with no harmful side effects.
more images: from Greg Piepol of Rockville, Maryland; from Adrian Guzman of San Jose, California.
DEWBOW: Not all rainbows are in the sky. Look carefully at this field of grass photographed on May 9th by Laurent Laveder of Chateaulin, Brittany, France. Can you see the rainbow running faintly down the middle?
"Dewbow" would be a better name for it, says Laveder. He's right. This rainbow is caused by dew. Little droplets of water hanging on to blades of grass catch the rays of the morning sun, spreading them into the colors you know so well. (True rainbows are formed in the same way, only the droplets are up in the air.)
In a second picture, Laveder caught a strange halo around the head of his shadow. This is caused by dew, too. It's called heiligenschein.