A celestial body orbiting the sun that displays some diffuseness or a "tail" of debris that generally points away from the sun. Both the diffuseness and tail (coma) are composed of gas and dust of various atomic or molecular compositions. The coma material comes from a small nucleus that is usually invisible. The head of the comet seems to be made of solid particles, some of which are frozen gases, while its tail is made of tiny particles so far apart that stars can be seen through it. A comet is visible because of the reflection of sunlight on its head and gaseous tail. Comets travel around the sun with its tail always pointing away from the sun. Some comets reappear every few years. Others pass by the sun once and never return.
The head has been observed to be as much as 30,000 to 1,000,000 miles in diameter and the tail (when near the sun) has sometimes appeared to be 200million miles in length
Almost 1000 different comets have been reported http://cfa-www.harvard.edu/iau/Ephemerides/Comets/index.html
One of the more famous comets is Halley's Comet. It has been recorded since 204 B.C. It seems to reappear every 75 years.
People used to be very superstitious and afraid of comets because they thought it brought disaster and death. They even thought the earth could be destroyed by a comet. It was thought in recent times that comets were quite harmless bodies in the solar system.
With the impact of Shoemaker-Levy into Jupiter that is no longer held with certainty.
What are Asteroids?
They are the thousands of little planetoids between Mars and Jupiter. The asteroids that have been charted range in size from 20 to 8o miles in diameter. Asteroids may have been formed from a large planet that broke into smaller pieces as a result of some cosmic collision, Each asteroid has its own individual orbit around the sun.
In our solar system many pieces of rock and metallic substances travel in various orbits. Some weigh only a few grams, while others weigh many tons Occasionally the Earth pulls these substances from their orbits and into Earth's atmosphere. Friction caused by their high speed through the atmosphere sets the meteoroids on fire. As it burns , it gives off a bright light.
Ordinarily, a meteoroid burns up completely.
However, occasionally a meteor strikes the earth before being
up. One example of such an event was the
impact that caused the enormous Arizona
crater 4/5 of a mile wide and 570 ft. deep into solid
the cosmic mystery of the century may be an example of one that did
The Manson event was an unimaginable catastrophe. The
impact of the
enormous meteorite caused destruction equivalent to approximately 10
tons of TNT. Everything within 130 miles of the point of impact
instantly engulfed in flames. Trees were
standing vegetation was devastated within 300 miles of the
site. It is also believed that most animals as far as 650 miles
did not survive ...,and dinosaurs 800 miles away would have been
off their feet.
The Western Interior Seaway was home to many forms of marine vertebrates, which would have greatly disturbed or killed by giant shock waves and possible tsunami-like waves. The seaway's habitats would have been so disrupted as to cause the death of thousands of marine creatures. To support this theory , scientists have found evidence that certain lineages of fish ,mosasaurs and marine turtles...mysteriously vanished from the Western Interior Seaway during the approximate time of the Manson Impact event."
The quote and photo from
Photo courtesy of Joe Tucciarone
Potentially hazardous asteroids can be accessed at http://cfa-www.harvard.edu/iau/lists/PHACloseApp.html
The possibility of impact with a piece of comet or a piece of an asteroid with our planet needs to make tracking of these objects imperative.