So, what are the main targets that astronomers study? Let’s start with stars — the heart of astronomy studies. Our Sun is a star, one of perhaps a trillion stars in the Milky Way Galaxy. The galaxy itself is one of countless galaxies in the universe. Each one contains huge populations of stars. Galaxies themselves are collected together into clusters and superclusters that make up what astronomers call the “large-scale structure of the universe”.
Our own solar system is an active area of study. Early observers noticed that most stars did not appear to move. But, there were objects that seemed to wander against the backdrop of stars. Some moved slowly, others relatively quickly throughout the year. They called these “planetes”, the Greek word for “wanderers”. Today, we simply call them “planets.” There are also asteroids and comets “out there”, which scientists study as well.”