Astronomers wanted to get better measurements of the positions of the stars. This was not only important for science but also for navigation. Sailors had learned how to use the stars to guide their way at night and they needed better measurements to get a better idea of where they were. Special tools called astrolabes and quadrants, and later on sextants, were made to measure the position and angle of objects in the night sky. By using these tools people made very good maps of the stars. But, there was still no way to get a closer view of planets and stars, or to look deeper into space.