1. Comets
Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. When a comet's orbit brings it close to the sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the sun for millions of kilometers.

2. Quick facts
-More than 3000 comets have been discovered -May take hundreds or even 1000s of years to orbit the sun -240 BC was the earliest sighting of a comet Halley's Comet is arguably the most famous comet. It is a "periodic" comet and returns to Earth's vicinity about every 75 years, making it possible for a human to see it twice in his or her lifetime. The last time it was here was in 1986, and it is projected to return in The comet is named after English astronomer Edmond Halley, who examined reports of a comet approaching Earth in 1531, 1607 and He concluded that these three comets were actually the same comet returning over and over again, and predicted the comet would come again in 1758.

3. Kuiper belt
Astronomer Gerard Kuiper, in 1951, theorized a disc-like belt of icy bodies exists beyond Neptune, where a population of dark comets orbits the sun in the realm of Pluto

4. comets
Comets only have tails when they are close to the sun. When they are far from the sun, comets are extremely dark, cold, icy objects. The icy body is called the nucleus. Nuclei are made of various types of ices, dirt and dust. As comets get closer to the sun in their journeys through the solar system, they start to warm up.

5. comets
As they reach an area roughly the same distance from the sun as Jupiter, the ices start to heat up and vaporize, releasing the gases and embedded dust particles that form a cloud or atmosphere -- called a coma -- around the comet. As comets continue traveling closer to the sun, the dust particles and other bits of debris in the coma are blown away from the sun due to the pressure of sunlight. This process forms a dust tail. If this tail is bright enough, we can see it from Earth when the sunlight is reflected off the dust particles. Comets usually have a second tail too. This one is called an ion or gas tail and it is formed when the ices of the nucleus are heated and turn directly into gases without passing through the liquid stage -- a process called sublimation. The gas tail forms when charged particles from the sun, called the solar wind, push the cometary gas particles directly away from the sun. The gas tail is visible because its particles glow after being excited by solar radiation. Once comets start moving away from the sun, their activity decreases. Their tails fade and the coma disappears. They return to just the icy nucleus again. When comets' orbits eventually bring them back towards the sun, the coma and tails begin to form again.

6. formation
About 4 billion years ago, our sun was just beginning to take shape as a star. As the sun got warmer and warmer, a cloud of ice and dust surrounded the early sun. As the cloud formed, it started rotating. It also slowly changed from a spherical shape to one that was flatter, shaped more like a donut with the sun in the hole. The cloud whirled around and around and the rotating cloud got flatter and denser. In the area of the cloud most distant from the sun, dust and ice particles came together and stuck to each other. Over millions of years, these particles got a little bigger. Eventually these particles grew to the size of basketballs and then cars and buildings. Finally, these particles grew to the size of city blocks. Many of these objects in the distant solar system became known as comets.

7. missions
20 missions to comets Most recent mission: Rosetta spacecraft landed on a comet in 2015
Rosetta will also help to discover whether comets contributed to the beginnings of life on Earth. Comets are carriers of complex organic molecules, delivered to Earth through impacts, and perhaps played a role in the origin of life. Moreover, volatile light elements carried by comets may also have played an important role in forming Earth's oceans and atmosphere.

8. Place a bag inside of another bag.
Comet Recipe!
Place a bag inside of another bag.
Fill a styrofoam cup with water (from SIDE sink) and add to bag.
Fill a plastic cup with soil and add to bag
Add a dropper of NH3
Mix up solution in bag
See me for dry ice and let it sit for a few minutes
YOU MUST WEAR GOGGLES, APRON, AND GLOVES AT ALL TIMES!