Another factor is the type of star. If we are looking for planetary systems that might have intelligent life, then we need to narrow our search for middle aged yellow stars like our sun. Stars more massive than the Sun live a fast and furious life, there is not time enough for intelligent life to develop. Our Sun is known as a G class star, and that s the type astronomers narrowed their search to. The next thing to know, is what to look for.
All stars are so far away that they only appear as dots even in the most powerful telescopes.
Planets are much smaller than stars and so there is no chance of ever seeing them. By studying the light from a star, and examining its spectrum, astronomers can learn a great deal about the star. As a planet orbits a star, the planet s gravitational influence pulls on the star making it change both speed and direction very slightly. The more mass an object has, the stronger the force of gravity. Because of this, the star does not quite move in a straight line at a steady speed.