Stargazing: December comet could be spectacular

Wayne Harris-Wyrick: Comet ISON grazed the sun on Thanksgiving and is poised to come away from the sun as one of the brightest comets in centuries ... or not.
Published: December 3, 2013

There may be a brilliant comet in your evening sky, visible right after sunset.

I say “may be” because as of this writing, it had not yet passed around the sun. On Thanksgiving Day, Comet ISON dipped into the sun's outer atmosphere. If it survived the heat and gravitational stress, it came out with a massive and bright tail and will pass relatively close to Earth in mid-December. Some scientists estimate it will be as bright as a full moon right after it loops around the sun, the brightest comet in centuries.

But comets have a way of disappointing. There were some indications in late November that the comet already was fragmenting, which means it may not even make it around the sun before it disintegrates, something many sun-grazing comets have been known to do. But, if you can see it this evening, it probably survived the sun and may remain visible to the naked eye until near the end of January. And if it's not now visible from Earth, well, comets are unpredictable.

Sudden impact

Thirty-five million years ago, a massive asteroid or comet slammed into the Atlantic Ocean just off the East Coast of the United States. It hit near what is now Virginia and created the Chesapeake Bay, the largest estuary and the largest meteor crater in the United States.

That impact also buried water from an ancient ocean that formed about 145 million years ago. It is the oldest large body of seawater ever identified on our planet.

The crater is 56 miles wide and groundwater under the crater represents a piece of the ancient ocean. The water contains twice as much salt as modern seawater, which helps distinguish it from fresher, and younger, groundwater beyond the buried edge of the crater.

“We knew from previous observations that there is deep groundwater in quite a few areas in the Atlantic Coastal Plain around the Chesapeake Bay that have salinities higher than seawater,” said Jerad Bales, acting USGS associate director for water. “Various theories related to the crater impact have been developed to explain the origin of this high salinity. But, up to this point, no one thought that this was North Atlantic Ocean water that had essentially been in place for about 100 million years. This gives us confidence that we are working directly with seawater that dates far back in Earth's history.”

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