The word "comet" comes from the Greek word for "hair." Our ancestors thought comets were stars with what looked like flowing hair trailing behind.

 

 
 

 

For centuries, scientists thought comets traveled in the Earth's atmosphere. In 1577, observations by Danish astronomer Tycho Brahe showed that they actually traveled far beyond the moon.

 

 
   
 

 

Sir Isaac Newton (1642-1727), the great English scientist, discovered that comets move in elliptical (egg-shaped) orbits around the Sun. He also thought that comets were members of the Solar System, just like planets, and that they could return over and over again. He was right!

 

 
 

 

As early as the 1700's, scientists began developing mathematical formulas that could predict the orbit of a particular comet around the Sun. At that time, calculators and computers didnít exist, so everyone had to do the calculations by hand!

 

 
  Most astronomers in the 1500's and early 1600's thought that a comet came once and was never seen again. They believed that a comet approached the Sun in a straight line, spun around it, and then disappeared into space in a straight path.