Comet ISON’s remains in good health and in one piece as it approaches the sun today at over 150,000 mph (243,000 km/hr). At 36.8 million miles, the comet has arrived at nearly the same distance from the sun as the planet Mercury. The average surface temperature on that planet’s sunny side is 800 degrees F (430 C), so we can begin to appreciate how steamy it must be getting on Comet ISON.
All that solar energy vaporizes ice from the comet’s nucleus; light pressure and the solar wind blast dust and gases trapped in the ice back to form a tail.
Observers are reporting that the comet is easily visible still even in twilight through 10×50 binoculars and small telescopes. One observer suspected seeing it with the naked eye, but you’ll almost certainly need some kind of optical aid to make the most of your own attempt dawn ISON vigil. Magnitudes for the comet range from about 3.5 to 4.0.
Suzy Webb of Brisbane, Australia shares her observation from this morning:
“Through my 10×60 binoculars it was easy to spot and had a slight bluish tinge. It resembled a bright fuzzy round patch. There was some elongation to the north. No tail is visible.”
Once ISON rose higher, Webb pointed her 4-inch reflector its way:
“Wow – I couldn’t get over how blue comet ISON is; especially considering the sky is now showing blue from twilight emerging. Blue on blue- very pretty. The sky is now too bright to see any fuzzy halo or an elongation. All that could be seen is the bright central condensation in the shape of a round blue ball.”
Alan Hale, co-discoverer of Comet Hale-Bopp, saw Comet ISON at magnitude 3.9 with a tail 1.5 degrees long (three full moons wide) in his 10×50 binoculars. He described the comet’s head as “stellar” or star-like in appearance.
ISON has now slipped under the gaze of NASA’s STEREO Ahead orbiting solar observatory. While the image is low resolution, it’s exciting because we should now have constant views of ISON from STEREO and (very soon) the much higher resolution coronagraph on the orbiting Solar and Heliospheric Observatory (SOHO). SOHO will see the comet beginning the 27th.
(For updated daily maps to help you find Comet ISON, please click HERE.)