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- Friday the 13th, December 13, 2013, we will see the Geminid meteor shower. Between 100 and 120 meteors are expected every hour. Morning viewing is best after the bright Moon has set. Meteor showers are when the Earth passes through the dust tail of a comet.
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- Our human ancestors have been around for 100,000 years and you can see where evolution has taken us. Here I am dictating to a typewriter. Dinosaurs were around for 100,000,000 years, 1000 times longer and they were eliminated in a matter of hours. They could survive tremendously extreme environments, adapting to all kinds of survival conditions, but, they could not survive one asteroid that was 10 miles in diameter. The flash of heat sent around the world set the atmosphere on fire. 90% of all the species on land and in the ocean were extinct in a matter of hours and days. The dust in the atmosphere blocked the sunlight for years. Only the "small" or the "deep" survived.
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- The Defense Department has been watching meteors for 25 years. But, it was in secret. The military was using satellites looking down on the upper atmosphere for rocket launches signaling a nuclear attack on the United States. When astronomers finally got to see the data they were flabbergasted. Our upper atmosphere gets regular impacts from meteors that were never seen. Fortunately, our military learned that these were not a nuclear attack requiring our own missile launchings. And fortunately astronomers got the data to plot some of these graphs.
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- The graph of the data covers a tremendous range from space dust to giant asteroids. To get this condensed it is better to plot the logarithm of the data. The “ x” axis in the log of the mass in grams. The “ y” axis it the log of the number of impacts per square kilometer per year. This simple scale of logarithms, or exponents, goes from -10 to +20 grams on the horizontal axis. That is the range from 10^-10 to 10^20 grams. 10^20 grams is 10^17 kilograms, which is 10^14 tons, which is 10^8 megatons, or 100,000,000 megatons. That’s big.
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- There are 5 categories of meteors from Zodiac light which is space dust , to meteors and meteorites, to Moon craters, to Apollo Comets.
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- The end points for the curves plotted for each category are given in the table below, ---------------------------------------------------(x , y) : ------ ( log grams, log impacts)
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----------------- Zodiac light ---------- ( -11, 10 ) -------- ( -5 , 4 ) -------
----------------- Meteors --------------- ( -5, 4 ) --------- ( 2 , -4 ) -------
----------------- Meteorites ------------- ( 2, -4 ) --------- ( 9 , -10 ) -------
----------------- Moon craters --------- ( 2, -4 ) ---------- ( 14 , -15 ) -------
----------------- Apollo Comets ------- ( 9, -12 ) -------- ( 20 , -18 ) -------
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- This table could be repeated showing the anti-logs with the logs as the exponents. For example:
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------------------ Zodiac light ---------- ( 10^-11, 10^10 ) -------- ( 10^-5 , 10^4 ) -------
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- x is the mass in grams
- y is the number of impacts per square kilometer per year.
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- ZODIAC LIGHT:
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- From the table above the mass of the dust varies from (-11) log grams to (-5) log grams. The anti-logs are from 10^-11 to 10^-5 grams. The period at the end of this sentence is 6*10^-6 grams, or 0.000006 grams. An ant weighs 10^-2 grams. So you can see this is very fine space dust.
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- We would expect to see a large number of impacts of this space dust. The number ranges from 10^10 to 10^4 impacts per kilometer^2 per year. The surface of the Earth is 51*10^7 kilometers^2.
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- The number of impacts of 10^-11 size space dust on the surface of Earth’s atmosphere is 51*10^17 impacts per year. There are 3.16 *10^7 seconds in a year, so that is 16*10^10 impacts per second, 160,000,000,000 impacts per second of 10^-11 gram space dust.
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- The Earth is flying through a blanket of space dust. The dust collects in the upper atmosphere causing rain to fall but other than that there's not much damage. It's not the same with meteors and meteorites. Meteors mostly burn up in the upper atmosphere. Meteorites are larger, or harder, and make it through the atmosphere to hit the ground.
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- METEORS AND METEORITES:
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- Meteors range in mass for 10^-5 to 10^2 grams.
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- Meteorites range in mass from 10^2 to 10^9 grams. That is from 100 grams to 1,000,000 kilograms.
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- How often does a 100 gram meteorite impact 1 km^2 each year? 10^-4 is 0.0001 times the area of the Earth 510,000,000 km^2 = 51,000. 100 gram meteorites impact the Earth 51,000 times each year. A year has 8,760 yours. Therefore, the 100 gram meteorite impact occurs 6 time each hour.
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- MOON CRATERS:
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- We will skip over moon craters and leave it for the reader to do some of these calculations.
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- APOLLO COMETS:
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- Let's move on to Apollo comets. These are comets that cross back and forth, inside to outside, Earth's orbit around the sun. They are called" Earth-crossing comets".
---------------------- Log ( 15, -15 )
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-------------------- anti-Log (10^15 , 10^-15 )
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- The mass of an Apollo comet can be 10^15 grams, or 10^12 kilograms. A Blue Whale weighs 10^5 kilograms. A fully loaded oil tanker weighS 10^8 kilograms. So, an Apollo comet can have a mass equivalent to 10,000 oil tankers.
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- However, these 1000 megaton impacts do not happen very often. The number of impacts = (10^-15 / km^2) * (51 * 10^7 km^2) = 51 * 10^-8 years.
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- This would be 5 times in a billion years or once every 200 million years.
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- COMETS THAT HAD AN IMPACT:
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- There are 200 proven sites where meteorites struck the Earth‘s surface. The most famous struck the Yucatán Peninsula 65 million years ago. It was 10 miles in diameter causing 90% of extinction of life on Earth.
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- Chelyabinsk comet that exploded over Russia in February, 2013, was 50 feet in diameter weighing 11,000 tons. (See the review #1567 "The Russian Meteor" to learn more about this event.)
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- On June 30, 1908 the Tunguska meteor exploded over Russia at 8 kilometers altitude. It was 10 times bigger than Chelyabinsk. It leveled an area the size of San Francisco. Fortunately, it was all trees that got destroyed. No people were in that part of Siberia at that time. In fact, it was 17 years later that scientists finally visited the area to determine the asteroid had exploded with 5,000,000 tons of energy.
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- The Barringer Crater was a meteor that hit 50,000 years ago in the Arizona desert. It was a nickel- iron asteroid. The impact left a crater 3/4th of a mile across and 750 feet deep. The impact explosion was equivalent to 2,500,000 tons of TNT.
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- An asteroid discovered in 2004 is 1,350 feet across. After calculating its orbit astronomers give it a 1 in 300 chance of hitting the Earth on April 13, 2029.
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- Halley's comet made a flyby of the Sun in 1986. It will loop by again in the year 2061. The period of the elliptical orbit is 75 years. It is potato-shaped, 10 miles long and 6 miles wide. The length of its orbit extends beyond the orbit of the planet Neptune 4,860,000,000 kilometers wide.
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- The comet passed Saturn's orbit in 1989, so, it took three years to cover that distance of 1,300,000,000 kilometers. Do the calculation, it averaged 30,695 miles per hour.
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- To go from Uranus to Neptune’s orbit it took 12.5 years to cover 1,600,000,000 kilometers. It is slowing down to 9,074 miles per hour.
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- Halley’s comet tail is the source of the Orionid meteor shower that we get to see every October.
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(1) See Reviews:
- #1557 Tektites in Healdsburg, California
- # 1611 Meteor Impacts
- #1567 The Russian Meteor
- #1017 Meteorite and Asteroids
- # 547 Shooting Stars
- # 719 Geminid Meteor Shower
- # 523 The Story of a Rock.
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RSVP, with comments, suggestions and corrections. An index of all reviews is available. Some reviews are at: -------------------- http://jdetrick.blogspot.com
,or: email request for copies to: ------- jamesdetrick@comcast.net
or: ---- https://plus.google.com/u/0/ ,or, “Jim Detrick” ------- www.facebook.com,
------ www.twitter.com or cell: 707-536-3272 ------ Thursday, December 12, 2013
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