ASTEROID FLYBY: Approaching from the direction of the sun, mountain-sized asteroid 2015 JO25 will fly past Earth on April 19th approximately 1.8 million km away. NASA says there is no danger of a collision. This unusually bright space rock is about twice as reflective as the Moon. Amateur astronomers may be able to see it in backyard telescopes as a magnitude 11 speck of light during and after the flyby. Got an image? Submit it here.
SOLAR WIND STREAM APPROACHES EARTH: A hole has opened in the sun's atmosphere and it is directly facing Earth. NASA's Solar Dynamics Observatory photographed the structure bisecting the solar disk on April 16th:
This is a "coronal hole"--a place where the sun's magnetic field opens up and allows solar wind to escape. Solar wind emerging from this hole could reach Earth as early as April 17th.
NOAA forecasters estimate a 55% chance of polar geomagnetic storms when the solar wind arrives on April 17-18. Arctic twilight will mute the visibility of Northern Lights, but might not overwhelm them completely if the auroras are bright. Monitor the aurora gallery for sightings. Free: Aurora Alerts.
DOUBLE RAINBOW: Whenever you see one rainbow, look for another, because rainbows always come in pairs. Consider this example, photographed by Kamila Mazurkiewicz Osiak of Trzcianki, Poland, on April 13th:
"This huge double rainbow appeared after an intense rainstorm passed through our area," says Osiak. "It was raining so hard, it looked like the clouds were walking on the ground."
The bright inner rainbow is the primary bow, caused by sunbeams reflecting once inside falling raindrops. It's the bow you usually see. The less-bright outer rainbow is the secondary bow, caused by sunbeams reflecting twice inside raindrops. Secondary bows often go unnoticed, because they are usually very faint, but they are always there.
In Osiak's case, "you couldn't miss it," she says. Bright sunlight lancing through the clearing clouds struck droplet-laden air behind the retreating storm, resulting in an unusually intense secondary bow.
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