Since the time of Galileo, astronomers who have wanted to see farther into space have developed advanced telescopes to observe finer details of celestial objects. Reflecting and refracting telescopes use different technologies with mirrors and lenses. Observatories use large telescopes, while planetariums allow observers to project images of the sky onto a large screen to study celestial elements. By using spectroscopes or spectrometers, astronomers can discover the gases of each star, their density, and even their temperature. Astronomers use a variety of tools to observe and measure characteristics of objects far in space.