A Christmastime comet is headed our way
Earthlings should be treated to a beautiful holiday surprise in December, Comet Wirtanen 46P.
Dr. P. Clay Sherrod, the researcher, educator and author whoseArkansas Sky Observatories are renowned as "America's oldest private research science and observatory facility," wrote, "as this comet is slowly closing in on perihelion this Dec. 16 (closest pass by the sun) it will also swing closely by Earth four days later in December and it perhaps might be as bright as 3rd magnitude, or even a bit brighter. That is easily naked eye visible and certainly should be a treat in binoculars."
Sherrod added that its proximity to Earth means it will be moving relatively fast at its closest approach on Dec. 19. It won't seem to move when viewed, even through a telescope, he said, but on an hour-to-hour basis an observer should be able to see that it has changed its position.
An exciting factor is that from Dec. 15-18, as Sherrod wrote, the comet will move between two famous star clusters, the Hyades and the Pleiades, and likely will be visible to the unaided eye at that time. The clusters also are easily seen without binoculars or telescopes.
Spaceweather.com said astronomers are calling Wirtanen "the comet of the year." The site explains in an Oct. 16 posting, "two months from now, on Dec. 16, the kilometer-wide ball of dirty ice will come within 11.5 million km (about 7.1 million miles) of Earth — making it one of the 10 closest-approaching comets of the Space Age. Comet 46P/Wirtanen will probably become a naked eye object for several weeks during the holidays."
Comets in culture
Until recent centuries, comets have been observed and feared as supposedly evil portents. In an article titled "Comets in Ancient Culture," Noah Goldman of the University of Maryland, College Park, writes that "to some cultures the tail of the comet gave it the appearance of the head of a woman, with long flowing hair behind her. This sorrowful symbol of mourning was understood to mean the gods that had sent the comet to earth were displeased. Others thought that the elongated comet looked like a fiery sword blazing across the night sky, a traditional sign of war and death."
Shakespeare's "Julius Caesar" reflects the ancient Romans' dread of bad tiding brought by these strange objects. Calpurnia, Caesar's wife, has a bad feeling about his venturing out to the Senate on the ides of March. Awful omens have been seen and heard, including graves giving up their dead, spectral squadrons in the clouds battling and drizzling blood on the Capitol, "and ghosts did shriek and squeal about the streets."
Squealing ghosts would be enough to keep me in the villa, let alone blood drizzles. But Caesar replies, eh, what will be will be, and anyway the predictions fit the world in general, not especially him.
Calpurnia has a rebuttal:
"When beggars die, there are no comets seen; The heavens themselves blaze forth the death of princes."
These omens mean you, she's saying. He brushes aside all concerns and — well, we know what happens next.
Around the world
In the mythology of India, Ketu is Comet, the beloved seer who has a snake body. Vedas relate that a demon who caused eclipses, Rahu, managed by trickery to imbibe a few drops of the celestial ambrosia that conferred immortality. Rahu had a snakelike or fishlike lower body.
"However, the Sun and the Moon gods had witnessed Rahu’s deed," notes Patrick Das Gupta of the Department of Physics and Astrophysics, University of Dehli in India.
In the article "Comets in Ancient India," he continues, "so, the demon tried devouring them, whereupon Vishnu (a main deity) severed its head by hurling his deadly discus, the Sudarshan chakra, at Rahu."
Since they were immortal, the parts of the demon became two living entities, Rahu with the head and Ketu with the bottom. "In the absence of a torso, the Sun or the Moon could not be retained for long after being swallowed by the head Rahu. … That was the way Hindu mythology dealt with the phenomena of eclipses."
An article archived in the Hindu Dharma Forums relates, "The severed head was taken by Simihika the mother of Asura Swarbhanu and nursed patiently. The head over a period of time got the body of Serpent and he was named Rahu. A Brahmin named Mini took the body. He brought up this body as his own son. To this body Lord Vishnu granted a serpent's head. This became Ketu who in the due course of time became a saintly and revered seer.
"Rahu and Ketu have not forgiven Sun and Moon for exposing them and they cause Eclipse."
Where comets get started
We now know that comets are material left over from the formation of the solar system, the majority of which reside in the Kuiper Belt and the Oort cloud. The belt "is a disc-shaped region beyond Neptune that extends from about 30 to 55 astronomical units (2.7 billion miles to more than 5 billion miles from Earth). …
"There may be hundreds of thousands of icy bodies and a trillion or more comets in this distant region of our solar system," says NASA. Short-period comets, those that take less than 200 years to circle the sun, often start there.
The Oort Cloud is far beyond the Kupier Belt. It's a vast shell of icy material starting about 186 billion miles to 465 billion miles from the sun, and extending to around 4.6 trillion miles. "This is about a quarter of the distance to the nearest star, Proxima Centauri," adds theplanets.org. It says objects in the cloud are composed of water ice, ammonia and methane, and that long-period comets are believed to originate there. Perhaps they are nudged toward the sun by interaction with other comets or the gravity of a passing star.
A NASA science site describes comets as "cosmic snowballs of frozen gases, rock and dust that orbit the sun. When frozen, they are the size of a small town. When a comet's orbit brings it close to the sun, it heats up and spews dust and gases into a giant glowing head larger than most planets." Tails of dust and gas point away from the sun, stretching for millions of miles in space. Remains of comets sometimes hang along the trail, and whenever Earth passes through these, the tiny bits of dust cause meteor showers as the particles burn up in Earth's atmosphere.
Needless to say, if a comet were to impact Earth, that would be bad. But we have nothing to fear from Wirtanen and celestial beauty to anticipate.
Joe Bauman writes an astronomy blog at the-nightly-news.com and is an avid amateur astronomer. His email is firstname.lastname@example.org.