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- Halley’s comet visits us and the inner planets once every 75 years. An event that happens once in a human lifetime. Hopefully we each get to see it once. I saw it in 1986. The comet orbit’s the Sun in a distant elliptical orbit extending out to the Oort Cloud, returning back again in 75 years, 2061.
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- Humans have been recording the comet’s visits for 2, 256 years. That’s right the first recorded visit is in Chinese dated 240 BC. It was referred to as the “ broom star”.
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- The Babylonians recorded the comet in 164 BC and 87 BC Another recording in Chinese was dated 12 BC. There was speculation that Halley’s Comet may have been the real star of Bethlehem. The comet appeared again in 66 AD.
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- In 837 AD it came the closest to Earth passing within 3,200,000 miles. The Moon is 238,855 miles away.
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- It was in 1705 that Edmond Halley used Sir Isaac Newton’s equations and calculated that the comet would return in 1758. He died before that happened, but, he got to name the comet. He had observed the comet himself in 1682. Kepler had observed it in 1607
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- The comet’s orbit period is 75.3 years, so, it has made 30 loops since the Chinese first started recording the visits.
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- By 1910 the comet was known to have a retrograde orbit, meaning the opposite direction of the planets, and very elliptical. It passed Earth within 13,900,000 miles that year.
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- The Earth’s orbit passes through the tail of the comet twice in each year. These are called the Aquarid and Orionid meteor showers. The names refer to the Star Constellations the shooting stars seem to fall from.
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- Halley is referred to as a long-period comet although most in this classification have 200 year orbits. These comets originate from the Oort Cloud that is a collection of icy bodies orbiting the Sun but some 50,000 times the Earth-Sun distance.
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- Another classification is short-period comets having an average period orbit of 6.5 years. These comets are heavily influenced by the gravity of Jupiter.
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- Comets are referred to as “ dirty snowballs” having an envelop of gas that sublimates from their surface as they approach the Sun. Sublimate means that the volatile ices on the surface transform from solid to gas directly due to the Sun’s radiation.
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- In 1986 several spacecraft visited Halley’s comet. Their discoveries determined the nucleus to be the shape of a peanut. It was very dark reflecting on 4% of the light. It was 10 miles long and 5 miles wide. Its density was 0.6 grams per cubic centimeter. Water density is 1 gram/cm^3. This low density implied that Halley was a loose collection of smaller pieces. Its surface was adverse landscape of hills, ridges, and craters covered with a thick layer of dusty ice.
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- The gas tail, coma, extended out 62,000 miles. The material in the gas was dated to by 4,500,000,000 years old. The same age as the birth of the Solar System.
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- The next visit is 2061. Someone else is going to have to write about this one. I got to see the 1986 visit. There are still several mysteries to solve. For example: Halley’s maximum temperature occurs at perihelion, when it is closest to the Sun. However, its maximum brightness does not occur until 11 days later. Why is that?
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- On February 1991, 5 years after perihelion, Halley experienced a mysterious explosion. It brightened to magnitude 6.7. A brightness increase of 470 times normal that lasted for several months before subsiding. What happened?
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- 2,256 years of study and we are still learning with more to learn. How great is that?
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RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email upon request. Some reviews are at http://jdetrick.blogspot.com Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net. ---- “Jim Detrick” -- www.facebook.com, -- www.twitter.com, -- 707-536-3272 Monday, January 28, 2013
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