EARTH DODGES SOLAR FLARES: Solar activity is moderately high this week, but the eruptions (including an X-flare on Nov. 19th) have had little effect on our planet. The flare sites are concentrated near the sun’s SW limb where a cluster of active sunspots is rotating off the Earthside of the sun. NOAA forecasters estimate a waning 20% chance of M-class flares and a 1% chance of X-flares as the active regions depart. Solar flare alerts: text, voice
ISON, THE DAWN COMET: Comet ISON is plunging toward the sun and brightening as it heads for a perilous close encounter on Nov. 28th. This morning, with the “final countdown” clock at T-7 days, Juan Carlos Casado photographed the sundiver over the Teide Observatory in the Canary Islands:
“The comet is over the distant island of Gran Canaria,” he says, “while in the central cloud we can see the planet Mercury. ISON was at the limit of naked-eye visibility, but it was an easy target for my SLR camera with a small telephoto lens (85 mm focal length) on a static tripod and 6 seconds of exposure.”
Because Comet ISON is moving into the rosy glow of dawn, it will soon be impossible for cameras on Earth to track it. NASA’s fleet of solar spacecraft are about to take over. Later today, Comet ISON will enter the field of view of the STEREO-A spacecraft. The Heliospheric Imager on STEREO-A will pick up the comet just as Earth-bound telescopes begin to lose it. In the days that follow, STEREO-B, SOHO and the Solar Dynamics Observatory will join the hunt, providing continuous views of Comet ISON all the way to perihelion (closest approach to the sun) on Nov. 28th. Stay tuned!
WHY IS COMET ISON GREEN? Taken by hundreds of people around the world, the pictures of Comet ISON we receive every day vary widely in quality, context and camera settings. However, they all seem to have one thing in common: the comet looks green. Why? To answer this question, Italian amateur atronomers Paolo Corelli and Dario Comino used a high-dispersion spectrometer to analyze light from the comet’s atmosphere. Here are there results:
The spectrum of Comet ISON is dominated by a green spectral line from diatomic carbon (C2). This substance is common in the atmospheres of comets, and it glows green when illuminated by sunlight in the near-vacuum of space. The spectrum also shows a weaker but still significant blue emission line from C2. Comet ISON’s mixture of green and blue light gives it the aqua hue seen in many long-exposure photographs. Finally, the spectrum reveals a contribution from atomic oxygen. This element is familiar to readers of spaceweather.com as a source of green light in auroras.