Earlier in the 20th century, Hubble and others resolved individual stars within certain nebulae, thus determining that they were galaxies, similar to, but external to, our Milky Way Galaxy.
A inicios do século XX, Hubble e outros distinguiron estrelas individuais dentro de certas nebulosas, determinando así que eran en realidade galaxias, similares, pero exteriores, á nosa galaxia a Vía Láctea.