origins of meteors:
asteroids collide and bits of all sizes ranging from microscopic dust to chunks kilometers across break off. Some of these bits are thrown into an earth crossing orbit. When one of these bits enters the earths atmosphere the friction causes a great deal of heat energy which ionizes the gases along its path thus coursing the familiar meteorite trail (shooting star). These are in addition to those caused by comet debris. When the particles survive entry through the earths atmosphere they become meteors. This depends on the composition and density of the particle, its size and its speed of entry relative to the earths atmosphere.
near earth objects (NEOs):
NEOs are small bodies in the solar system (asteroids and short period comets) with orbits that regularly bring them close to earth, and which, thus are capable someday of striking earth.
those NEOs with orbits that actually intersect the earth's orbit are called Earth Crossing Objects (ECOs) and those potentially able to hit earth are called Potentially Hazardous Asteroids (PHAs)
earth's atmosphere protects us from NEO's smaller than 50m diameter
NEOs from 50m to 1km diameter may cause massive local damage or tsunamis if impacting the ocean. The last hit Siberia in 1908 with energy of 15 megatons. Such NEO's hit earth once every 200 yrs on average.
NEO's > 2km diameter (1 million megatons energy) would create an impact winter with loss of crops worldwide & subsequent starvation & disease. These strike earth once or twice every million years.
it is now thought by many that the end of the Permian age 250m yrs ago (ie. before dinosaurs) was due to a NEO which hit earth and plunged earth into darkness & freezing cold, caused volcanoes & released hydrogen sulphide gas, wiping out 90% of sea life & 80% of land life globally - the "Great Dying" in addition to setting off the separation of the continents from the unified Gondwana land mass. The possible sites are either:
Gosse Bluff in NT, Australia, is a huge crater formed when a comet crashed to earth 130 million years ago
the dinosaurs were probably wiped out at the end of the Cretaceous period some 65 million yrs ago by a NEO of 15km diameter (100 million megatons energy) hitting Chicxulub on Mexico's Yucatan peninsula
there are ~1000 NEA (near earth asteroids) larger than 1km & perhaps a million larger than 50m and max. size is some 25km.
there are many more comets than NEA's but as they spend the majority of their orbits well away from the earth, they contribute only ~10% to the census of objects that may strike the earth.
as of 2003, only 60% of the larger NEO's have been discovered and none are projected to hit earth in the next 100yrs, but we would have no warning at all for an undiscovered one impacting us. NASA's Spaceguard Survey aims to discover 90% of NEO's > 1km by 2009.
it may be possible to develop a way of altering the orbit of a known NEO by 2015 but for this to prevent an impact, it must be tried first to see if it works and then have 10yrs prior warning so that a significant alteration of the orbit can be made. See News Article- Astronauts Rusty Schweickart and Ed Lu on deflecting an NEA
NEO surveillance programs:
funded by NASA & uses a pair of 1metre 5mpixel CCD GEODSS telescopes & from 1996 to March 2004 had discovered 128 comets and detected ~200,000 new asteroids
funded by NASA, two autonomous observing systems at Maui & Mt Palomar using 1.2 metre (48") telescopes, operating since 1995
amount of meteors hitting earth:
200 tons per day
100 billion cosmic dust sized particles enter the atmosphere each day.
25 million grain of sand size enter
annually, 24,000 small pea size to fist sized meteors that reach the earths surface totals about 10 tonnes of which 3.33 tonnes land on land. This gives a bombardment rate of 40 meteorites per square km of land surface per year over a period of a million years. That's a lot of space junk just lying around waiting to be picked up - check your roof guttering with a magnet.
500 kg or less of meteors are found each year
Stone meteorites make up 80% iron meteorites 18% and stony-iron 2% of the total.
Impact craters come in all sizes but less than one in every 100 years is formed that is larger than the meteorite.
Killer meteorites strike once in every 100,000 – 1,000,000 years.
Of all the living beings that have died since the earth began, meteors have killed more than all the other causes put together.
Living beings observed to have been killed by a meteorite - one – a dog in Egypt.
June 30, 1908, multimegaton Tunguska blast in Siberia
Feb 12, 1947, Sikhote-Alin impact
Aug 10, 1972, A very bright daylight fireball appeared in the skies of the western United States and Canada on August 10, 1972. It was seen by a large number of people, most notably many camera-bearing tourists located in Grand Teton, Yellowstone, and Glacier national parks. The trail was seen for 26secs, creating sonic booms indicating it got as low as 60km high, and crossed 1500km of atmosphere without impacting earth. It's estimated size of 1000 metric tons would have created an impact explosion greater than the 2 atomic bombs dropped on Japan.
Oct 9 1992, a widely witnessed & photographed fireball broke into fragments with one hitting a car netting the owner a tidy sum for both the car & the 12kg impactor
March 26 2003, a meteor the size of a car broke apart in the upper atmosphere, showering debris all over the Chicago suburb of Park Forest damaging 6 houses & 3 cars. More than 18kg of meteorite fragments were recovered.
October 2003 - meteor causes sonic boom over Perth
June 2004 - 0.5kg meteor smashes through residential tiled roof in Auckland, bouncing of lounge suite
June 2006 - meteor perhaps > 90kg hits a mountainside in Norway - see news
meteors hitting the moon:
example Leonids Nov 2003:
data for meteor showers usually give:
The figure ZHR which is zenithal hourly rate. This is the number of meteors that a single observer would see per hour if the shower's "point of origin", or radiant, were at the zenith and the sky were dark enough for 6.5 magnitude stars to be visible to the naked eye.
"Illumination" gives an idea of how dark the sky is, the lower the figure, the darker the sky.
outside of the showers, you can still see sporadic meteors.
rates seen from the Southern Hemisphere are around 6 random meteors being seen per hour during the late morning hours and 1 per hour during the evening. The evening rates will be reduced during the times around the full Moon due to interference by the Moon's light.
Since Meteors are relatively rare, very fast and usually unpredictable, the best time to photograph meteors is during one of the annual "Meteor Showers" like the August 10-12th Perseids or better yet during one of the rare Leonid Meteor Storms on November 17-18 of 1998 and 1999. Meteor showers are caused when the earth's orbit intersects a comit's orbit causing the comet's tail debris to fall to earth as meteors. Meteor storms are massive meteor showers like the Leonid Meteor Storm that happens every 33 years and can produce up to 100,000 meteors per hour when the Earth intersects comet Temple - Tuttle's debris dead center.
data for the meteor showers can be found at:
you need very sensitive film or digital camera as the fast moving meteors do not give much time for photons to build up on any one spot => 800-3200ASA with fast lens at least f2.8, then maximum exposure time will be limited by either light pollution or star trails from unguided camera. You may find a low light mode video camera useful.
great comet & meteor photos can be taken with relatively simple equipment:
a 35mm adjustable camera, tripod, a cable release and a fast film like Fuji 800 or faster.
50mm lens shots taken with regular 35mm SLR camera on tripod for 30 second exposures at f/1.8 .
set the camera on the tripod with lens wide open (about f/1.8) and using the cable release trip the shutter for 30 seconds. Since the earth rotates pretty fast at 1000mph (25,000miles/24hours) exposures longer than 30 seconds using a 50 mm lens will show star streaks on the film. That's OK if you want the interesting pattern of star trails but for comets & meteors, star trails detract from your main subject.
135 mm shots taken with 35mm SLR camera mounted "piggyback" on top of a telescope on an equatorial mount to allow guided exposures of stars.
Cross hairs were placed on the eyepiece and the telescope was used "like sights on a gun" to point the camera at the comet and keep it in center view while tracking the comet with manual hand controls for the time exposure of about 5 minutes. The process is tedious but is the only way to take long exposures over 30 seconds without more sophisticated clock drive equipment that many modern astrophotographers use.
find a good dark location (away from city lights) and one that has something of interest in the foreground that you can include in the picture.
Perseids 2004. Canon 1D Mark II with a 17-40mm F4L lens set at 17mm F4, ISO 3200, MWB 3500K, riding piggyback on an LX200. Composite of 28 x 30 second exposures, selected from 680 exposures taken over the course of about 6 hours. Stacked 9 exposures for the background, and then used painted masks in Photoshop to insert the 19 exposures that had meteors.
caused by dust from Halley's comet
a good one for Australia, especially north of latitude 30degS
radiant at 14h 56m and +48deg declination thus not good for southern observers
on June 27th, 1998, northern sky watchers were surprised when meteors began to stream out of the constellation Bootes. They saw as many as 100 meteors per hour during a 7-hour-long outburst. It wasn't the first time: similar outbursts from Bootes had been recorded in 1916, 1921 and 1927. Astronomers call these unpredictable meteors the June Bootids.
The source of the June Bootids is comet 7P/Pons-Winnecke, which orbits the Sun once every 6.37 years. The comet follows an elliptical path that carries it from a point near the orbit of Earth to just beyond the orbit of Jupiter. Pons-Winnecke last visited the inner solar system in 2002, laying down a new trail of dust and gas. Earth isn't due to hit material shed in 2002 for many, many years, but older dust trails from the 19th century are drifting across Earth's orbit. These could be responsible for the outburst observed in 1998 and a possible new surge of meteors in 2004.
2004 shower only visible from western USA at 1100 UT 23/6/04
Compositing photos of meteor showers:
Here's a technique posted by Fred Buenjes: