To
Graham:
FYI, the word "neigh" refers to the vocalized sound that a horse makes, dontcha know?
Meteor Entry into the AtmosphereWhen they plow through the atmosphere, meteors are heated to more than 3000 degrees Fahrenheit, and they glow. Meteors are not heated by friction, as is commonly thought. A phenomenon called ram pressure is at work. A meteor compresses air in front of it. The air heats up, in turn heating the meteor.
The intense heat vaporizes most meteors, creating what we call shooting stars. Most become visible at around 60 miles up. Some large meteors splatter, causing a brighter flash called a fireball, and an explosion, which can often be heard up to 30 miles away. When meteors hit the ground, they're called meteorites. Some meteors are bits broken off asteroids, others -- mere cosmic dust -- are cast off by comets. A meteoroid is an object in space that may, if it enters our atmosphere, become a meteor.
Meteor BreakupWhether an object breaks apart depends on its composition, speed and angle of entry. A faster meteor at an oblique angle suffers greater stress. Meteors composed of iron withstand the stress better than those made of stone. Even an iron meteor will usually break up as the atmosphere becomes denser -- around 5 to 7 miles up.
Meteor Composition Because cometary nuclei are formed by a diversity of materials, including organics and ices, the fragments released from these nuclei should be also rich in these compounds. As the meteor plunges through the Earth's atmosphere, different temperatures will excite different chemicals within the meteorite, all while the friction created from the meteor breaking though the atmosphere are stripping it of its' chemical layers. The temperature and the chemical composition that ignites will determine the color:
sodium - orange/yellow
iron - yellow
magnesium - blue/green
calcium - violet
silicate - red
Doc