A SOLAR WIND STREAM APPROACHES: The density and temperature of plasma around Earth is increasing on April 18th as a high-speed solar wind stream approaches our planet. NOAA forecasters estimate a 55% chance of polar geomagnetic storms when the solar wind arrives. Free: Aurora Alerts.
ACTIVE SUNSPOT RETURNS: During the late hours of April 17th, something hurled a plume of hot gas over the eastern limb of the sun. NASA's Solar Dynamics Observatory photographed the splash:
The source of this activity is probably returning sunspot AR2644. In early April the active region produced a series of M-class solar flares and shortwave radio blackouts. Now, following a two week trip around the farside of the sun, AR2644 is due to return. Amateur astronomers with solar telescopes are encouraged to monitor the sun's eastern limb for signs of the old sunspot. If it returns with any of its old potency, solar flare activity could increase sharply in the days ahead.
SCINTILLATING SIRIUS: Sirius is the brightest star in the sky. It is also, arguably, the most colorful. On any given evening of northern Spring, sky watchers can behold a spray of rainbow colors emanating from the Dog Star as it sets low in the southwestern sky. Tom Wagner of Waterloo, Iowa, has developed a beautiful way to display the star's hue. "Decades ago I discovered that by wiggling my binoculars while looking at Sirius, I could easily see the colors of the rainbow flash by in rapid succession." On April 16th he took this picture through the eyepiece:
"This is a 2 second exposure," he says. "The colors were spectacular!"
Astronomers call this phenomenon "scintillation." Also known as "twinkling," the phenomenon is caused by thermal irregularities in Earth's atmosphere. As packets of relatively warm and cool air drift in front of a star, the star's light is refracted. The prismatic action of these air packets produce rainbow colors--especially near the horizon where starlight must pass through many turbulent irregularities to reach the observer.
All stars scintillate, but Sirius does so most flamboyantly because of its extreme brightness. See for yourself. Step outside this evening after sunset and look southwest for Sirius near the feet or Orion. The lower it gets, the more it twinkles. Enjoy the show!
Realtime Space Weather Photo Gallery