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Halley’s Comet only comes into the inner solar system about every 76 years. The last pass at its perihelion was in 1986 and I got a glimpse of it. The next one should be in 2016 and I won’t be around for that visit.

But Earth intersects Comet Halley’s orbit twice each year. Around now, we can see bits of this comet as the annual Eta Aquariid meteor shower. Then, in October, Earth’s orbit again intersects the orbital path of Comet Halley and the broken pieces from Halley’s Comet burn up in Earth’s atmosphere as the annual Orionid meteor shower.

The comet itself is a mountain of ice, dust and gas, but each pass near the sun breaks it up more and it sheds that trail of debris. Astronomers say it lost about 1/1,000th of its mass during its last flyby in 1986.

It is truly awesome (we tend to forget what awe really means) that Comet Halley has circled the sun innumerable times over countless millennia. I am doing my 65th circle this year and I surely have lost a lot over those orbits (though not mass).

A meteor shower can be from fragments (meteoroids) the size of grains of sand or gravel smashing into Earth’s upper atmosphere. This creates those vaporized fiery streaks (meteors) across our sky. I suppose we have our birthday candles

Right now, Comet Halley is outside the orbit of Neptune at almost its most distant point from us (aphelion).

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Earlier this month the Geminid meteor showers were visible to us and the Ursid meteor showers peaked at the solstice. I wrote last week about the theory that the Christmas Star of Bethlehem may have been a comet. Our 2016/2017 New Year comet visitor is the periodic comet 45p (AKA Honda-Mrkos-Pajdušáková).

I doubt that you and I will catch sight of Comet 45P.   It will be up there in the heavens now along with a crescent Moon. Being a periodic comet, it appears every 5.25 years. It is expected to reach maximum brightness and be closest to Earth in February 2017, but I have read online that it should be binocular and telescope visible to we amateurs sometimes from January through February 2017.

The comet will reach perihelion (closest to the Sun) tonight, December 29, 2016, which will increase its head and tail.  It passes just 7.4 million miles from the Earth on February 11th at 14:44 UT.

comet_67p

Comet 67P/Churyumov–Gerasimenko. By ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0, CC BY-SA 3.0-igo,

A comet is an icy body that releases gas or dust. They are often compared to “dirty snowballs,” though recent research has led some scientists to call them snowy dirtballs. Comets contain dust, ice, carbon dioxide, ammonia, methane and more.

When passing close to the Sun, a comet warms and begins to evolve gasses. This “outgassing” produces a visible atmosphere (coma) and sometimes also a tail.

Is a comet a “shooting star?” No, and a shooting (or falling) star has nothing to do with stars. Those streaks of light you can sometimes see in the night sky are caused by tiny bits of dust and rock called meteoroids falling into the Earth’s atmosphere and burning up. The short-lived trail of light the burning meteoroid produces is called a meteor. If any part of the meteoroid survives burning up and actually hits the Earth, that remaining bit is then called a meteorite.

A comet is a celestial body moving about the sun and it will not enter Earth’s atmosphere. They usually have a pretty eccentric orbit.

Comet 45P is towards the center of the Milky Way Galaxy in Sagittarius. At its brightest, it will be passing through the constellation Hercules during closest approach on February 11th. During the second week of February, the comet is visible in the dawn sky 82 degrees west of the sun at maximum brightness. This view will be best in the northern hemisphere.

Hale–Bopp

Comet Hale–Bopp seen from Croatia in 1997

 

painting

Adoration of the Magi by Florentine painter Giotto di Bondone (1267–1337).

I recall seeing a planetarium show around this time of year when I was a kid on a trip to the Newark Museum. Of course, we saw the planets and famous stars, but I remember that they showed us how Jupiter, Saturn and Mars were coming together and what it might have looked like above Bethlehem at the first Christmas.

The Star of Bethlehem was something I learned about as a kid in religious classes, and I saw it depicted quite literally above the creche that was under our Christmas tree. But I wasn’t that grown up when I began to wonder what star it was and why didn’t it have a scientific name.

I never got a good answer, and as I got older I discovered that there were several reasons why it was not an easy question to answer. First, there is uncertainty in the actual date of Christ’s birth. Second, the terminology used to describe celestial events 20 centuries ago are not what we use today.

Back then, any celestial object bright enough to be seen with the eye tended to be called a “star.” That is how meteors were described as “shooting” or “falling” stars. A comet was called a “hairy” stars. Novas would be called a “new” star. In this time before astronomy, even planets were viewed as “wandering” stars.

The painting Adoration of the Magi by Giotto di Bondone (1267–1337) shows the Star of Bethlehem looking like a comet above the Christ child. It is known that Giotto witnessed an appearance of Halley’s Comet in 1301 and that probably is what made him decide to depict it as a comet rather than a fixed star.

The Bible doesn’t say anything about a calendar date of the Nativity. Scholars look at references to people or events such as the reign of King Herod. We believe he died sometime between 4 B.C. and 1 B.C. by our present calendar. The Three Wise Men (Magi)  visited Herod just before he died and presumably the birth of Christ and the first appearance of the guiding star came sometime before that.

There is no evidence that Jesus was born in late December. A passage by Luke in the Bible –  “And there were in the same country shepherds abiding in the field, keeping watch over their flock by night” actually suggests that it was spring which was the time when shepherds in Judea were out at night tending the newborn lambs.

However, December 25 was the end of the week of the Roman festival of Saturnalia. Gifts were exchanged and homes, streets and buildings were decorated. Relatives often returned home for this holiday. The early Christians often used elements of pagan holidays in order o make the transition to Christianity more familiar and comfortable.

Those early Christians may have also chosen the date of the Saturnalia in order to avoid attention with their own celebration and so escape persecution. When Roman emperor Constantine officially adopted Christianity in the 4th century, the date of Christmas remained as December 25.

Christ’s birth also probably did not occur 2016 years ago. Our present numbering of years as AD or BC was conceived by the Roman abbot Dionysius Exiguus around 523 A.D. Dionysius placed 1 A.D. immediately following 1 B.C. and disregarded the mathematically required zero in between. We can’t completely blame him, since then in Europe zero was not considered a number. That makes our 3 B.C., actually –2, numerically speaking.

Dionysius also accepted a fairly common assumption of that time that Jesus was born in the 28th year of the reign of the Roman emperor Caesar Augustus. But Augustus was known in the first 4 years of his reign by his original name Octavianus, so that adds another possible error of 4 years.

Back to that star… Was there any unusual celestial occurrence between the years 7 and 2 B.C. that might have caught the attention of people or the Magi? I found four theories.

I like the comet theory. Either a comet or nova was seen by Chinese and Korean stargazers in about 5 BC. It was observed for over seventy days with no movement recorded. That would have given the Magi time to travel. But it would be odd to choose a comet to follow because in that time comets were seen not as good omens but as omens of bad things to come.

Halley’s Comet appeared in August and September in the year 11 BC, but that seems a bit too late to be what the Wise Men saw.

Another theory is that it was a nova or supernova outburst: That would be something that appears anew but leaves no trace for us to find in the future. Although their names imply a new creation, these spectacular objects are in reality dying stars, although they are new (but temporary) additions to the nighttime sky. Really bright novas are visible usually a few times in a lifetime. The most recent one I found listed appeared in August 1975 not far from the bright star Deneb in the constellation Cygnus.

There was one nova that appeared in the spring of 5 B.C. according to Chinese records, but it is described as not very prominent.

The least likely theory is that it was a meteor. But meteors move across the sky in seconds and are not candidates of a guiding light that could lead the Magi halfway across the Orient to Bethlehem.

The Comet of Bethlehem seems the best possibility. One might have been visible to the naked eye for a few weeks predawn or at dusk and its head and tail may have been a kind of compass pointer.

 

 

 

GiottoAdoration_of_the_Magi

The comet as the Star of Bethlehem in Giotto’s The Adoration of the Magi, 1305

May 25, 240 B.C.E.: Chinese astronomers Shih Chi and Wen Hsien Thung Khao chronicle the earliest recorded sighting of Halley’s comet at its closest approach to the sun (perihelion).

It wasn’t Halley’s comet because there was no Edmond Halley until the 18th century. Maybe it should be the Cinese Comet. English astronomer Edmond Halley thought that comets observed in 1531, 1607, and 1682 seem very similar and predicted that they were the same comet returning at regular intervals. He predicted it would return in 1758 and it did on Christmas Day. Halley had died by then, but his named was given to it.

It was after his death that astronomers looking back at earlier records based on Halley’s computation decided that the early Chinese record was this same comet. They also decided that a record of the appearance in 164 B.C.E. and one in 87 B.C.E. recorded on Babylonian clay tablets, and a famous 1066 appearance a few months before the Norman Invasion of England.

Mark Twain was born when it appeared in 1835, and in 1909, Twain said: “I came in with Halley’s comet in 1835. It is coming again next year, and I expect to go out with it.” He died on April 21, 1910, one day after the comet reached perihelion.

 

This week is the time of the annual Leonid meteor shower. The peak for 2012 Leonid will be tonight, November 17 at 3 a.m. EST. It was will be more visible because of the moonless weekend sky because the moon will have set by that time, so the reduced night won’t wash out any Leonids you may see.

The Leonids are associated with the periodic comet Tempel-Tuttle, first discovered in 1865. This comet has a period of 33.2 years, so it was last close to the sun in 1998 and it will return in 2031. After Tempel-Tuttle’s discovery, it was traced back to a comet observed in 1366.

When astronomers realized that Tempel-Tuttle’s last close approach to the sun was in 1833 and that it coincided with one a huge meteor storm, they began to realize that meteors had their origins in comets.

The supermoon put a little too much light into the night sky to see the Eta Aquarid meteor shower last night. It is one of two shooting star displays created by dust left over by Halley’s comet as it makes its 76-year trip around the sun. (The Orionid meteor shower in October is the other meteor show from the comet.)

If you have better conditions than I had in Paradelle – clear skies away from city lights – and went out before dawn, you might have caught a few fireballs before dawn.

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