BLUE GIANT

Blue stars are large and compact, this causes them to burn their fuel quickly which in turn makes their temperature very hot.  These stars often run out of fuel in only 10,000 - 100,000 years. 

A blue giant is extremely bright.  Like a lighthouse, they shine across a great distance.  Even though blue giant stars are rare, they make up many of the stars we see at night because they shine so brightly.

Blue giant stars die in a spectacular way.  They grow larger just like the sun-sized stars, but then instead of shrinking and forming a planetary nebula, they explode in what is called a supernova. Supernova explosions can be brighter than an entire galaxy, and can be seen from very far away.

YELLLO STAR

Like the Sun, these medium-sized stars are yellow because they have a medium temperature (remember the fire example?).  Their higher temperature causes them to burn their fuel faster. This means they will not live as long, only about 10 billion years or so.  Near the end of their lives these medium-sized stars swell up, becoming very large. When this happens to the Sun, it will grow large enough to engulf even the Earth. Eventually they shrink again, leaving behind most of their gas. This gas forms a beautiful cloud around the star called a Planetary Nebula. 

When will the Sun expand into a giant, and then shrink leaving behind a planetary nebula?
Don't worry, the sun is only about 5 billion years old. It still has another 5 billion years or so before it will expand and turn into a planetary nebula.

RED DWARF

Red Dwarf stars are smaller than our sun. And since they are smaller, they also have less mass. Because of their small size, these stars burn their fuel very slowly, which allows them to live a very long time. This also causes these stars to not shine as brightly as others. Some red dwarf stars will live trillions of years before they run out of fuel.

Why are red dwarf stars red?
Because red dwarf stars only burn a little bit of fuel at a time, they are not very hot compared to other stars. Think of a fire. The coolest part of the fire is at the top of the flame where it glows red, the hotter part in the middle glows yellow, and the hottest part near the fuel glows blue. Stars work the same way. Their temperature determines what color they are. Thus, we can determine how hot a star is just by its color.

Red dwarf stars are by far the most common type of star in outer space. However, very few stars that you see in the sky are red dwarfs. This is because they are so small and make very little light. Imagine standing on a mountain. Pretend that there are one million kids 5 miles away holding flashlights, and 20 miles away there is a lighthouse for ships. You will most likely not see any of the flashlights, while you will very easily see the lighthouse. If the flashlights all glowed as brightly as the lighthouse they would blind you. Likewise, if all the red dwarf stars glowed as bright as the bigger stars, our nighttime sky would be very bright.

THE CONSTELLATION