1:45 PM | An update on Comet ISON - still expected to be visible to the naked eye in late November

(April 2013 image of Comet ISON through Hubble telescope, courtesy NASA)

Discussion

Comet ISON was first spotted in September 2012 by scientists working with the International Scientific Optical Network (hence its name ISON) and it should become visible to the naked eye in the northern hemisphere in late November. As to how bright the comet will be at the end of the year, it is still somewhat unknown. ISON was once expected to set records for brightness and was dubbed the “comet of the century”, but astronomers now believe it won’t be quite as brilliant as originally thought and it is already dimmer than expected. A comet’s brightness depends not only on how close it passes to Earth and the sun, but also on its size and composition which makes predictions rather tricky.

For now, ISON can be seen in the northern hemisphere through telescopes – a faint smudge in the constellation of Cancer about 183 million miles from the sun. ISON is currently speeding through the cosmos at around 67,000 mph and is expected to accelerate to about 844,000 mph as it swings around the sun. By late November, ISON is expected to move to near 700,000 miles above the sun’s surface. Around this time and into December, astronomers expect that ISON will become visible to the naked eye low in the eastern sky, but it does not look like it will reach the brightness of the full moon as originally hoped. The last truly great comet viewable in the northern hemisphere was Hale-Bopp, which was first spotted in 1995 and remained visible for a record 18 months.