Re: What is the difference between the Aurora borealis and Heat Lightning?

For all practical purposes, aurora and heat lightning are as different as 
ladybugs and pepperoni pizza. 

Heat lightning is merely regular old lightning which occurs far enough 
inside a cloud that its light is diffused throughout the cloud. We generally 
refer to this kind of lightning when the storm producing the lightning is 
well off in the distance toward the horizon (and clear sky may even be 
overhead). Thunderstorms rarely extend beyond thirteen to fifteen kilometres 
in height, the altitude at which the troposphere (the layer of the 
atmosphere beginning at Earth's surface) and the stratosphere meet. 
Lightning itself does not extend significantly beyond this height, though 
other phenomena related to thunderstorms may extend far into the 
stratosphere. However, these phenomena (known as elves and sprites) are very 
difficult to observe, and have only just recently been proven to exist.

Aurora, on the other hand, occur at the outer extents of the Earth's 
atmosphere, in a layer known as the ionosphere. This layer ranges roughly 
from 85 to 110 km above Earth, and is so named because the gases there exist 
in ionic form. Rapidly moving particles from the sun can penetrate this 
layer, striking primarily oxygen and nitrogen atoms and causing them to 
radiate in the aurora's characteristic red or green colors. 

For a good site on aurora, visit

 http://logosphere@earthlink.net

You might also be interested in visiting

 http://
members.mint.net/n1bug/prop/aumon/aufr.html

which monitors aurora in real time. For great lightning pictures, my 
favorite site is the Australian Severe Weather Page, located at

 http://
australiansevereweather.simplenet.com/

and for an explanation and pictures of sprites and elves, go to

 http://www.sciam.com/explorations/012097sprites/
012097explorations.html

Happy skywatching!