What's in the sky tonight?
November 7, 2013
-The bulge of the crescent Moon points sunward — but not quite down to Venus in evening twilight. The Moon is currently 5° north of the ecliptic, while Venus is 4° south of it. (In fact, Venus is at its farthest-south declination, –27° 10′, since 1930!)
-AR1890, one of the biggest sunspots of the current solar cycle, has turned almost directly toward Earth. This raises the possibility of geoeffective eruptions in the days ahead. NOAA forecasters estimate a 45% chance of M-class flares and a 10% chance of X-flares on Nov. 7th.
-Comet ISON is now inside the orbit of Earth and racing toward the sun. Last night, astronomer Alberto Quijano Vodniza of Pasto, Colombia, recorded the comet moving through space at 103,000 mph (46 km/s). "The movie shows the comet's motion over 27 minutes," says Vodniza. Watch it again. "We also caught a satellite."
On Nov. 28th, Comet ISON will fly through the sun's atmosphere little more than a million kilometers above the sun's fiery surface. This raises a question: Is Comet ISON racing toward its doom? Astronomer Matthew Knight of the Lowell Observatory thinks the comet might withstand the heat:
"At its closest point to the Sun, the equilibrium temperature approaches 5000 degrees Fahrenheit, hot enough to cause much of the dust and rock on ISON’s surface to vaporize," says Knight. "While it may seem incredible that anything can survive this inferno, the rate at which ISON will likely lose mass is relatively small compared to how big it likely is. Assuming that the comet's nucleus is bigger than about 200 meters in radius (current estimates suggest it is 500-2000 m in radius), it will likely survive. It helps that the comet is moving very fast, about 400 km/s at perihelion, so it will not remain long at such extreme temperatures."
If Comet ISON does survive its encounter with the sun, it could put on a good show for backyard astronomers in the northern hemisphere in December. The next few weeks will tell the tale.
Astro Picture of the Day:
November 7, 2013
Source:
Was there ever another comet like ISON? Although no two comets are exactly alike, one that appears to have had notable similarities was Comet Kirch, the Great Comet of 1680. Like approaching Comet ISON, Comet Kirch was a bright sungrazer, making a very close approach to the surface of the Sun. Neither comet, coincidently, is a member of the most common group of sungrazers - the Kreutz group - populated by remnants of a comet that disintegrated near the Sun hundreds of years ago. The long tail of Comet Kirch is depicted in the above painting by Lieve Versheier. As pictured, some members of the foreground crowd of Rotterdam in the Netherlands are holding cross-staffs, an angle measuring device that predated the sextant. No one knows how Comet ISON will develop, but like Comet Kirch, it is expected to be brightest when very near the Sun, in ISON's case during last few days of November.