Stars
For thousands of years, human beings have looked into the night sky and wondered about what they saw. What were the sparkling objects above? How did they move? How far away were they? Were they all the same? Over time, stories were told about the night sky. The stories turned into myths and legends. Observations were also made about the night sky. These observations were the beginnings of astronomy. Many of the objects you can see in the night sky are stars, large objects in space that produce light. Stars are so far away that their light does not reach us for years. As light from so far away passes through our atmosphere, it is moved around so that the star seems to twinkle. Our galaxy, the Milky Way, contains more than 100 billion stars. Our own Sun is one of them. It’s the only star in our Solar System, and the star closest to Earth. But many of those other 100 billion stars are the centers of their own solar systems. A star’s color comes from its surface temperature. All stars are extremely hot, but the stars with the hottest surface temperatures are blue. Ones that aren’t as hot are red. Our Sun is somewhere in between the hottest and coolest stars. It glows yellow. A star’s brightness also comes from its surface temperature. The hottest stars are the brightest. The coolest ones are less bright. Again, our Sun is somewhere in between. Stars don’t last forever. When the hydrogen in a star runs low, the star can no longer sustain nuclear fusion. It no longer has the energy to turn hydrogen into helium. That’s when a star’s fire begins to cool and the star begins to die. As most stars cool, they turn red. When a large star dies it may leave behind a burned part. This part can collapse and absorb the light around it. This is a black hole, the end of a giant star. A star must be 10 to 15 times larger than the Sun in order to end as a black hole.