ABSTRACT
The modern study of the solar system began in the mid-nineteenth century, with the arrival of telescopes large enough to show the surfaces of the planets in some detail. When astronomers first started using radio telescopes, they soon found small sources of intense radio waves, which they called 'radio stars'. Mount Wilson that Edwin Hubble first showed that the Milky Way is just one galaxy among many, and that the universe is expanding. In in the 1920s, Edwin Hubble showed that the nebulae were distant galaxies, far outside the Milky Way. There are so many stars in the Milky Way Galaxy that there must be lots more planets out there too, and a good many of them must be quite like our Earth. Pulsars are the remnants of supernovae, stars that have exploded with unimaginable force.
