Star
Star (astronomy), massive shining sphere of hot gas . Of all the stars in the universe , our Sun is the nearest to Earth and the most extensively studied. The stars visible to the naked eye all belong to the Milky Way Galaxy, the massive ensemble of stars that contains our solar system (the Sun and its nine planets ). About 5,000 stars can be seen with the naked eye, although not all of these stars are visible at any given time or from any given place. With a small telescope, hundreds of thousands of stars can be seen. The largest telescopes disclose millions of galaxies, which may each contain over 200 billion stars. Modern astronomers believe there are more than 1 x 1022 stars in the universe (this number is very large, a 1 followed by 22 zeros). The largest stars, if placed at the Sun's position, would easily engulf Earth, Mars, Jupiter, and Saturn. The smallest white dwarf stars are about the size of Earth, and neutron stars are less than about 20 km (about 10 mi) in diamet