Wednesday 4th September 2019
We started our Welcome Back Social Evening with a good old chin-wag.
Some of our committee got to discuss our new website which looks promising.
We had two new people along Dave and John who were keen to talk cameras so I put them with Dave Sm.
There were another couple along who went off to look through a scope so I failed to get their names.
Next week we get back to normal with perhaps an Observing Evening or if it’s cloudy a talk by our chairman on Meteorites.
Wednesday 11th September 2019
Andrew said that next week we have our AGM and Ed with Observing Highlights for Sept and October. He also reported that in Chelmsford last Saturday a purple sunset was seen apparently due to a volcanic eruption. (The volcano was not local).
He said the full Moon on Friday was actually a Micro Moon as it occurs when the Moon is at apogee.
Ted said he was collecting Monies as it was subscription time.
Jim reported that the clubs scopes now included a 12 inch Lightbridge and a 6inch Dob.
Mike announced that he was giving the talk this evening on: Meteorites
Mike said that a Meteorite was an extra terrestrial object in space that enters the Earth’s atmosphere and reaches the ground. If it burns up on the way it is a meteor. Meteors are small perhaps up to 3mm in diameter. They begin to heat up at an altitude of 60 miles. Some of the light is due to the heating but most is due to ionisation. With stony meteorites only 1 or 2 mm melts.
The amount of ablation depends on the speed and angle.
As his talk progressed Mike took meteorites from his bag for us to look at. There was an incredible array form tiny mounted pieces to a 7kg stony iron example. He explained he needed them to help along his talks to children.
Mike told us about the Peekskill Meteorite and we saw a video clip of the event.
The Peekskill meteorite fell on October 9, 1992 among the most historic meteorite events on record. Sixteen separate video recordings document the meteorite burning through the Earth's atmosphere; whereupon it struck a parked car in Peekskill, New York Peekskill is an H6 monomict breccia its filigreed texture is the result of the shocking and heating following the impact of two asteroids in outer space. The meteorite is of the stony variety and approximately 20% of its mass is tiny flakes of nickel-iron. When it struck Earth, the meteorite weighed 26 pounds (12 kg) and measured one foot in diameter. The Peekskill meteorite is estimated to be 4.4 billion years old.
After having been slowed by the Earth's atmosphere, the meteorite was traveling at approximately 164 miles per hour (264 km/h) at impact. Peekskill smashed through a red 1980 Chevrolet Malibu finally coming to rest in an impact pit beneath the car. Seventeen-year-old Michelle Knapp, the car's owner, heard the collision from inside her home. She later described the sound as “like a three-car crash”. Hurrying outside to investigate the noise, Knapp found her car smashed and the meteorite weighing 27.28 pounds, still warm and smelling of sulfur, beneath it.
Knapp retrieved the meteorite, after which it was sold to a consortium of three dealers for $50,000. Today, small specimens of Peekskill sell for approximately $125 per gram.
Knapp had just purchased the car for $300. Immediately following the extraterrestrial impact, it was sold to Iris Lang, wife of renowned meteorite collector and dealer Al Lang, for $25,000. Since then, it has been on display in numerous museums throughout the world, including New York City's American Museum of Natural History and France's National Museum of Natural History.
The car, as well as the main mass of the meteorite (which currently weighs 890 grams), are now in the Macovich Collection of Meteorites. Additional specimens of the meteorite can be found in Chicago's Field Museum, the American National History Museum, and the Smithsonian.
Mike showed a map of the ’Strewn Field’ which is the name given to the distinctive pattern of debris over the terrain.
Peter Simon Pallas, (born Sept. 22, 1741, Berlin—died Sept. 8, 1811, Berlin), German naturalist who advanced a theory of mountain formation and, by the age of 15, had outlined new classifications of certain animal groups.
Pallasite - In 1772, Pallas was shown a 680-kg lump of metal that had been found near Krasnoyarsk. Pallas arranged for it to be transported to St Petersburg. Subsequent analysis of the metal showed it to be a new type of stony-iron meteorite. This new type of meteorite was called pallasite after him; the meteorite itself is named Krasnojarsk or sometimes Pallas Iron (the name given to it by Ernst Chladni in 1794).
Ernst Florens Friedrich Chladni 30 November 1756 – 3 April 1827) was a German physicist and musician. His most important work, for which he is sometimes labeled the father of acoustics, included research on vibrating plates and the calculation of the speed of sound for different gases. He gave his name to the distinctive patterns seen of some metallic meteorites when sliced.
Jean-Baptiste Biot was a French physicist, astronomer, and mathematician who established the reality of meteorites, made an early balloon flight, and studied the polarization of light.
Diogenes of Apollonia Ancient Greek: 5th century BC was an ancient Greek philosopher, and was a native of the Milesian colony Apollonia in Thrace. He realised that meteorites were not from Earth and said: - “With the visible stars revolve stones which are invisible, and for that reason nameless. They often fall on the ground and are extinguished, like the stone star that came down on fire at Aegospotami.”
Mike explained that meteorites are principally found in deserts and in the Antarctic they are carried along by the moving ice sheet and if a mountain range is in the way they are pushed to the surface and can be readily collected.
He said that 94% of meteorites are Stony, 5% Iron and 1% Stony Iron. Stony meteorites, the most common type, are generally composed of approximately 75 – 90% silicon-based minerals, 10 – 25% nickel-iron alloy; they are magnetic which is one way of identifying them from regular stones.
Chondrule, small, rounded particle embedded in most stony meteorites called chondrites. Chondrules are usually about one millimetre in diameter and consist largely of the silicate minerals olivine and pyroxene. From textural and chemical relationships, it is clear that they were formed at high temperatures as dispersed molten droplets, which subsequently solidified and aggregated into chondritic masses. This process occurred in space in earliest times before the planets accreted. How the chondrules were melted, however, is not understood. It seems likely that dust particles or planetesimals already in existence were melted by high-energy events such as high-velocity collisions and splashed about as droplets that quickly cooled and crystallized.
An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies.
Iron meteorites are very dense - much heavier than almost all terrestrial rocks - and will easily adhere to a magnet. Iron meteorites also contain a relatively high percentage of nickel - a metal very rarely found on Earth - and they display a unique feature that is never seen in terrestrial material.If sliced and etched with a mild nitric acid solution a strange pattern appears. The most common names for these figures are Widmanstätten pattern and Widmanstätten structure; however there are some spelling variations:
Allan Hills A81005 or ALH A81005 was the first lunar meteorite found on Earth. It was found in 1982 in the Allan Hills at the end of the Trans Antarctic Mountains, during a meteorite gathering expedition.
EETA 79001 - meteorite is classified as a shergottite and is primarily basaltic in composition. It is the second largest Martian meteorite found on earth, at approximately 7900 grams.
ALH84001 meteorite determined to have come from Mars and the subject of a contentious scientific claim that it contains the remains of ancient life indigenous to the planet. Recovered from the Allan Hills ice field of Antarctica in 1984, the 1.9-kg (4.2-pound) igneous rock is thought to have crystallized from magma on Mars.
Mike even had a pic of a meteorite found on Mars by one of the rovers.
He said that we are familiar from lunar pictures showing craters with central peaks.
Here on Earth we have craters the most famous one is Meteor Crater at 50m dia. it is a meteorite impact crater approximately 37 miles east of Flagstaff and 18 miles west of Winslow in the northern Arizona desert of the US.
Meteor Crater lies at an elevation of about 5,710 ft above sea level. It is about 3,900 ft in diameter, some 560 ft deep, and is surrounded by a rim that rises 148 ft above the surrounding plains. The center of the crater is filled with 690–790 ft (210–240 m) of rubble lying above crater bedrock. One of the interesting features of the crater is its squared-off outline, believed to be caused by existing regional jointing (cracks) in the strata at the impact site.
Australia has Wolf Creek crater at 875m dia. Also Henbury Meteorites Conservation Reserve contains 12 craters which were formed when a meteor hit the earth's surface 4,700 years ago. The Henbury Meteor, weighing several tonnes and accelerating to over 40,000 km per hour, disintegrated before impact and the fragments formed the craters.
An iron meteorite fell on the Sikhote-Alin Mountains, in south eastern Russia, in 1947. Though large iron meteorite falls had been witnessed previously and fragments recovered, never before in recorded history had a fall of this magnitude been observed. An estimated 23 tonnes. /p>
The Wold Cottage - Meteorite The meteorite the second largest recorded meteorite landed two fields away from The Wold Cottage on December 13th 1795; it created a hole more than a yard in diameter and 18 inches deep. The meteorite was handed over to the Natural History Museum in South Kensington and Mr. Edward Topham (resident at the time) erected an obelisk on the exact spot where it had fallen.
Barwell Meteorite Green Plaque, situated in the southern part of the village, close to the original meteorite fall Barwell and neighbouring Earl Shilton were the site of a meteor event when, on Christmas Eve 1965, the villages were showered with fragments, from an object about the size of a traditional Christmas turkey.
The Tunguska event was a large explosion that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June 1908 (NS). The explosion over the sparsely populated Eastern Siberian Taiga flattened 2,000 square kilometres of forest, and caused at least three human casualties. The explosion is generally attributed to the air burst of a meteoroid. It is classified as an impact event, even though no impact crater has been found; the object is thought to have disintegrated at an altitude of 5 to 10 kilometres rather than to have hit the surface of the Earth. The force was equivalent to 5m tons of TNT.
Leonid Kulik. In 1920 he was offered a job at the Mineralogical Museum in St. Petersburg. In 1927, he led the first Soviet research expedition to investigate the Tunguska event, the largest impact event in recorded history. He made a reconnaissance trip to the region, and interviewed local witnesses.
The Chelyabinsk meteor was a superbolide that entered Earth's atmosphere over Russia on 15 February 2013 at about 09:20 YEKT. It was caused by an approximately 20m asteroid with a speed of 19.16 ± 0.15 kilometres per second. It quickly became a brilliant superbolide meteor over the southern Ural region. The light from the meteor was brighter than the Sun, visible up to 100 km away. It was observed over a wide area of the region and in neighbouring republics. Some eyewitnesses also felt intense heat from the fireball. Many cars in Russia have dash cams.
The Chicxulub crater is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. A widely accepted theory is that worldwide climate disruption from the event was the cause of the Cretaceous–Paleogene extinction event, a mass extinction in which 75% of plant and animal species on Earth became extinct, including all non-avian dinosaurs. Circa 66mya.
Probably the best home talk ever.