Comet ISON update Nov. 21 – Healthy, blue and now in STEREO

Comet ISON photographed this morning Nov. 21, 2013 in false color (blue applied to a black and white image) show a bright, compact head and long, filmy tail. A short distance down the tail you can see a separate bright wisp. This may be a piece of tail snipped off by the solar wind or it might possibly be a vaporizing fragment. Credit: Joseph Brimacombe

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.

Comet ISON photographed with a 12-inch widefield telescope from Namibia this morning Nov. 21, 2013. Beautiful! The comet was only a couple degrees high when this photo was made. Click to enlarge. Credit: Gerald Rhemann

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.

Sketch made by Australian observer and comet hunter / discoverer Terry Lovejoy of Comet ISON in his 12-inch telescope this morning Nov. 21, 2013. Notice the comet’s color and the two “wings” on either side of the coma. Lovejoy described the comet as “very bright” in his scope. Credit: Terry Lovejoy

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:

The comet this morning Nov. 21 shot with a 55mm lens at f/4.5 (wide open) with a Canon T3i. Eight 10-second exposures at ISO 800 were aligned and stacked to make the photo. Credit: Brad Timerson

“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.

Comet ISON is now in view of NASA’s STEREO Ahead spacecraft. This photo was made early this morning Nov. 21 and includes the homeland and planet Mercury. Click to view more STEREO images. Credit: NASA

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.)

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

2 thoughts on “Comet ISON update Nov. 21 – Healthy, blue and now in STEREO

  1. Using the Harvard site of observations, I totaled the last 7 and came up with an average of what John Bortle had said for yesterday, a magnitude of 4.8 for ISON. Though the average date would have been Nov. 19 for that figure. That may sound dim, and could explain why some are still having trouble finding it. But the percentage of distance from the Sun on that date would have been around 7 percent of it’s distance since discovery. If we take 7 percent of the distance to the Sun, that it was on Nov. 19, you came within 2 or 3 hours of perihelion. I know this sounds optimistic. But, if the comet continues brightening at that rate, then the magnitude late Thanksgiving morning would be around -10. Lovejoy is averaging around 5.2. Most think that it is near it’s brightest. I am predicting a magnitude of 4.4 around Dec. 2. That is when the distance from the Earth starts getting more than twice as fast as it is getting closer to the Sun. The Moon will not interfere either. If both scenarios work out, we could have 2 very easy naked eye morning comets at the same time. I have not seen this in over 27 years of comet interest. The Spring of 2004 came closest to that. But you needed binoculars to see all 3.

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