Meteors

Everything we understand about the Universe comes from light emitted or reflected by objects. It'd be nice if we could get actual samples from them: physical specimens we examine in the lab.
Well, sometimes the Universe can be accommodating and allows us to hold it in our hands.

If we go outside on a clear dark, moonless night chances are very good if we see a shooting star.
A fiery dot leaving a long glowing trail behind it. What we’re actually seeing is a tiny bit of interplanetary debris: rock, Ice or Metal ramming through the Earth’s atmosphere, heated to incandescence. Most are faint but some can be astonishing bright.
Shooting stars aren’t actually stars, Sometimes it seems like astronomers use different names for objects to keep things as confusing as possible.

In this case, the actual bit of solid stuff coming from space called Meteoroids. The phenomena of the meteoroid getting hot and blazing across the sky are called Meteor and when it hits the ground, we call it Meteorite. 
A typical meteor that we’ll see is due to a meteoroid that’s tiny probably smaller than a grain of sand! The meteoroid is orbiting the sun, probably at speed of few dozen kilometers per seconds. As it approaches the Earth, our planet's gravity accelerates it an additional 11km’s per second which is Earth Escape’s velocity. And when it enters our atmosphere it’s moving very fast up to 70km/sec or even more.

Meteoroids may usually be small, but they’re screaming fast and have a huge amount of kinetic energy, As they hit our atmosphere they slow from their orbital speed to nearly a standstill and their energy get converted into light and heat and that’s why we see a meteor.

 A big misconception about meteors is that they get hot due to friction with air; actually, a far bigger contributor to heat is compression.
One of the basic laws of physics is when we compress a gas it heats up. And meteoroids coming down with a hypersonic speed compresses the air in front of it, heating it hugely.
The gas can reach a temperature of thousands of degree Celsius for a few seconds.
The Air radiates away this heat, in turn heating up the meteoroid. The material on the surface vaporizes and blows away – and this process is called Ablation. 

That ablated material leaves a glowing trail behind the meteors, which we call a Train. Sometimes it can glow for several minutes, getting twisted up in high altitude winds, leaving behind an eerie, and ghost-like a persistent train. This all happens high above our head, about 90-100km above the ground.

Typically from one location, we can see a few meteors per hour. It may not seem that much but when we add all them up over the planet we find the Earth is getting pelted to the tune of about 100 tons of material a day.

But most of these meteoroids are very small and these random meteors are called Sporadic Meteors. They tend to be rocky in composition, and generally come from Asteroids. If two asteroids smack into each other, the collision can eject little bits of material that then orbit the sun. If their orbit crosses the Earth, then we have a potential meteor. 

It may take a few million years, but at some point, the Earth and the meteoroids are at some place at the same time, sometimes meteoroids travel in packs and we get Meteor showers, many dozens or even hundreds of meteors seen per hour with one exception those don’t come from Asteroids. They come from Comets.

When a comet orbits the sun, the ice on it turns to gas, dislodging dust and gravel mixed in. This material leaves the comet and tends to stay more or less in the same orbit as the comet itself. Over time, that material gets scattered all along the orbit, creating a puffy ribbon of tiny pieces of space debris around the sun.

When the Earth blows through that cloud of debris we get a meteor shower.  The point in the sky where the meteors come from is called The Radiant and the shower is named after the constellation the radiant in.
We have The Perseid Meteor shower, The Leonids and since the Earth hits a specific comet stream around the same time every year, the shower is annual, The Perseids are in Augusts and the Leonids in November.

The Earth plows into the meteoroids, so facing the direction of Earth’s orbital motion means more meteors. After local midnight we’re on the part of the Earth-facing into the orbit, so we see more meteors.
Annual Geminds showers occur in December that comes from the Asteroids 3200 Phaethon, which is on an orbit that takes it very close to the sun.

It’s possible it gets so hot that the rock vaporizes making it act like a comet. The vast majority of meteoroids is small and tends to burn up in our atmosphere but they can be bigger.

A bolide or fireball is an extremely bright meteor, and those can be about the size of the grapes.

Very rarely, incoming meteoroids will survive all the way to the ground and become a meteorite. Sometimes, the immense pressure of ramming Earth’s air causes the incoming meteoroid to crumble or even explode raining down dozens or hundreds of smaller pieces.

Meteorites are classified into three broad categories, Stony, which are mostly rock; Iron which are mostly metal: stony iron which is a mixture of the two.

The majority of meteorites are found are the stony type, the stony meteorites are subdivided into two kinds Chondrites and Achondrites. Chrondrites contains chondrules, small grains of minerals. These are very primitive and are thought to have condensed out of the original disk of material that formed the solar system. Their age can be found by looking at ratios of elements in them formed from radioactive decay. The oldest known meteorite 4,568 billion years ago; before the earth itself.

Achondrites don’t have chondrules in them, Most likely they come from a bigger Asteroid, one that was once molten through mixing the mineral.  A big collision disrupted the parent body, creating the Achondrites meteoroids.

Iron meteoroids most likely come from the center of a large asteroid, one big enough that metals fell to the center via gravity; Again, a big impact a blew the Asteroid up scattering its material around the asteroid belt, and with some on orbits that eventually intersected Earth.

Stony-iron is the rarest some have green or orange crystals of a mineral called Olivine embedded in a web of metal called pall sites they any are the most beautiful of all meteorites...