Does lightening travel from ground to cloud or cloud to ground?
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Lighting can travel ground to cloud, cloud to ground or cloud to cloud
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Lightning and thunder actually occured the same time. Only light travels faster than sound, so we see lightning before hear thunder.\n\nLightning is actually negative charges (electron) which jump to positive charges. How this charges formed?, Well, simply by the cloud moving in the sky.\n\nCloud 'rub' against air particle and positive and negative charges formed. Negative charges tend to appear at the botom or cloud while positive charges tend to appear at the top.\n\nWhen two clouds collide, the negative charges 'jump' to the positive charges (massively). This produces light and sound,, like normal spark, (only its a giant spark in the sky),\n\nSometimes lightning is dangerous becoz some positie charges 'dropped' to the ground, and the eloctron jumps to the ground, (a human standing there will be Bad Luck)
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The first process in the generation of lightning is the forcible separation of positive and negative charge carriers within a cloud or air. The mechanism by which this happens is still the subject of research, but one widely accepted theory is the polarisation mechanism. This mechanism has two components: the first is that falling droplets of ice and rain become electrically polarised as they fall through the atmosphere's natural electric field, and the second is that colliding ice particles become charged by electrostatic induction. Once charged, by whatever mechanism, work is performed as the opposite charges are driven apart and energy is stored in the electric fields between them. The positively charged crystals tend to rise to the top, causing the cloud top to build up a positive charge, and the negatively charged crystals and hailstones drop to the middle and bottom layers of the cloud, building up a negative charge. Cloud-to-cloud lightning can appear at this point. Cloud-to-ground lightning is less common. Cumulonimbus clouds that do not produce enough ice crystals usually fail to produce enough charge separation to cause lightning.\n\nWhen sufficient negatives and positives gather in this way, and when the electric field becomes sufficiently strong, an electrical discharge occurs within the clouds or between the clouds and the ground, producing the bolt. It has been suggested by experimental evidence that these discharges are triggered by cosmic ray strikes which ionise atoms, releasing electrons that are accelerated by the electric fields, ionising other air molecules and making the air conductive by a runaway breakdown, then starting a lightning strike. During the strike, successive portions of air become conductive as the electrons and positive ions of air molecules are pulled away from each other and forced to flow in opposite directions (stepped channels called step leaders). The conductive filament grows in length. At the same time, electrical energy stored in the electric field flows radially inward into the conductive filament.\n\nWhen a charged step leader is near the ground, opposite charges appear on the ground and enhance the electric field. The electric field is higher on trees and tall buildings. If the electric field is strong enough, a discharge can initiate from the ground. This discharge starts as positive streamer and, if it develops as a positive leader, can eventually connect to the descending discharge from the cloud.\n\nLightning can also occur within the ash clouds from volcanic eruptions[1],[2], or can be caused by violent forest fires which generate sufficient dust to create a static charge.\n\nA bolt of lightning usually begins when an invisible negatively charged stepped leader stroke is sent out from the cloud. As it does so, a positively charged streamer is usually sent out from the positively charged ground or cloud. When the two leaders meet, the electric current greatly increases. The region of high current propagates back up the positive stepped leader into the cloud. This "return stroke" is the most luminous part of the strike, and is the part that is really visible. Most lightning strikes usually last about a quarter of a second. Sometimes several strokes will travel up and down the same leader strike, causing a flickering effect. This discharge rapidly superheats the leader channel, causing the air to expand rapidly and produce a shock wave heard as thunder.\n\nIt is possible for streamers to be sent out from several different objects simultaneously, with only one connecting with the leader and forming the discharge path. Photographs have been taken on which non-connected streamers are visible such as that shown on the right.\n\nThis type of lightning is known as negative lightning because of the discharge of negative charge from the cloud, and accounts for over 95% of all lightning.\n\nAn average bolt of negative lightning carries a current of 30 kiloamperes, transfe
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Of course, laser is light.  Light travels in a vacuum, how do you think you can see the sun, and the stars?  Because light travels through space.  In fact, laser are routinely flashed towards the moon, to the reflector the astronauts of Apollo mission left there. The time it takes for the  light to come back allows to compute rthe distance form the Earth to the moon with grat accuracy.\nLaser light can travel in all medium that are not opaque.  Vacuum: very well.  Air?  Not as well, as there is dust and air itself scatters ligth somewhat.  Water?  A bit less than in air still, owing to the higher refraction index.  Same thing for glass.  But a brick?  A piece of wood?  No.
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Northern lights originate from our sun. During large explosions and flares, huge quantities of solar particles are thrown out of the sun and into deep space. These plasma clouds travel through space with speeds varying from 300 to 1000 kilometers per second. \n\nBut even with such speeds (over a million kilometer per hour), it takes these plasma clouds two to three days to reach our planet. When they are closing in on Earth, they are captured by Earth's magnetic field (the magnetosphere) and guided towards Earth's two magnetic poles; the geomagnetic south pole and the geomagnetic north pole.\n\n\n\nOn their way down towards the geomagnetic poles, the solar particles are stopped by Earth's atmosphere, which acts as an effective shield against these deadly particles.\n\nWhen the solar particles are stopped by the atmosphere, they collide with the atmospheric gases present, and the collision energy between the solar particle and the gas molecule is emitted as a photon - a light particle. And when you have many such collisions, you have an aurora - lights that may seem to move across the sky. \n\nIn order for an observer to actually see the aurora with the naked eye, about a 100 million photons are required.\n\n\nFor more info :-\nhttp://www.northern-lights.no/english/what/cause.shtml
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Lightning originates around 15,000 to 25,000 feet above sea level when raindrops are carried upward until some of them convert to ice. For reasons that are not widely agreed upon, a cloud-to-ground lightning flash originates in this mixed water and ice region. The charge then moves downward in 50-yard sections called step leaders. It keeps moving toward the ground in these steps and produces a channel along which charge is deposited. Eventually, it encounters something on the ground that is a good connection. The circuit is complete at that time, and the charge is lowered from cloud to ground. \nThe return stroke is a flow of charge (current) which produces a luminosity much brighter than the part that came down. This entire event usually takes less than half a second.
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Rayleigh Scattering. It occurs to all colors of light, but blue light is far more effected. Light traveling tangential to the atmosphere gets redirected to earth as it interacts with the atmospheres gas molecules. And as there is more ligth traveling tangential to the atmosphere in places farther from the suns position in the sky, there is more blue light scattered in these places. This makes the sky more blue say on the horizon than directly above at noon.
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Besides light and heat, they actually aren't similar at all. Fire is caused by an exothermic chemical reaction involving oxygen gas. Lightning is caused by electrostatic discharge between the ground and clouds, or between clouds.
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The exact reason is not proven, but suspected that it is because precipitation falls to the ground carrying electrons, and the lightning occurs when the difference in charges between the clouds and the ground even out, and the electrons jump back to the clouds.  That is why lightning is said to go from ground to the clouds.
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That kind of lightning are usually called  cloud to clud lightning, and  occurs  at very high altitudes between clouds at different altitudes (1,000 ft,).  there's no thunder because  the charges are  not  making ground like when they touch  earth.
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Since lightning is produced from the ground up, yes, it is on the ground before you see it.
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Because it travels along the least obstructed air.  As air is sometimes denser at certain elevations the lightning flows along the path of least resistence.
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Let me answer this way:  The static charge built up between the clouds and earth (ground) cause the air between to become ionized (lightening) causing a discharge of (usually) millions of amperes of current, neutralizing (minimizing) the charge.\n   And as you know, an efficient arrestor is designed to prevent any great voltage rise during the discharge.
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Yes, it is possible for lightning to strike water.  It happens all the time.  Lightning is the result of a difference in potential between two bodies.  When the potential is great enough, electricity jumps from the negatively charged body to the positively charged body.  The two bodies can be a cloud and a tree, a cloud and the ground or a cloud and water or from one cloud to another.  Therefore, lightning can be cloud to ground, cloud to cloud or even within a cloud.  What happens when the lightening bolt strikes the water is that at the immediate point of the strike, the temperature of the water instantly reaches the boiling point.  Given the extreme temperature of a lightning bolt and the extreme charge, I would suspect that not only is steam formed but a plasma is also likely formed at the immediate point of the strike.  As to what happens to any biological life at the point of the strike, it would depend on how near they are to the strike.  The closer they are to it, the more likely that they could be killed by the sudden change in temperature and potential.
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Sheet lightning goes from cloud to cloud.  Lightning is caused when electrical charge accumulates within clouds.  When fork lightning happens, the charge accumulated in a cloud is discharged to the ground.  When sheet lightning occurs, two different cloud masses accumulate opposite changers until they discharge.\n\nThe voltage required to discharged is directly related to the distance between objects and the dielectric constant of the medium (i.e. air).
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Some of these answers are good ones.  Clouds are charged, scientists can't agree why.  The tops of clouds are positively charged, the bottoms are negatively charged.  The negative charge at the bottom of the cloud repels negative ions in the earth's surface, which gives it a positive charge.  There are things called leaders and step leaders that seek out a path to relieve the difference in electrical potential.  As they reach out, then 'streamers' are generated on the opposing surface, like the ground, in response to the growing electrical field.  When these two meet this prepares the way for a lightning strike.  Usually this happens from cloud-to-ground, but it can also happen ground-to-cloud.\n\nOne of the best descriptions of how lightning strikes work can be found at http://science.howstuffworks.com/lightning5.htm
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Well electricity needs a path to travel in. Electricity can flow in wires, or other conductors, like a plasma, which consists of charged particles; that is, the electrons have been stripped off the atoms because they are so energetic, leaving just a seething collection of positive and negative particles (said to be "ionized"). In a lightning strike, a path of charged particles extends between the cloud and the ground, or some other object near the ground like a tree or a lightning rod or building (or sometimes between one cloud and another). The electricity in lightning follows this charged path. \n\nIf you can use a powerful laser or some other technique to form an ionized path in the air, then electricity can follow that ionized path, just like it does in lightning (or in Van de Graff generator experiments).