Barnard's Galaxy is a barred irregular galaxy approximately 1.6 million light-years away in the constellation Sagittarius. Part of the Local Group of galaxies, it was discovered by E. E. Barnard in 1884 with a six-inch refractor telescope. It's one of the closer galaxies to the Milky Way. It's similar in structure and composition to the Small Magellanic Cloud. It's about 7,000 light-years in diameter.

Edwin Hubble identified 15 variable stars in this galaxy. He also surveyed the galaxy's stars distribution down to magnitude 19.4. He provided spectral characteristics, luminosities and dimensions for the five brightest "diffuse nebulae" (giant H II regions). This included the Bubble and Ring Nebula. He also computed the absolute magnitude of the entire galaxy.

Hubble's detection of eleven Cepheid variable stars was a milestone in astronomy. Utilizing the Cepheid Period-Luminosity relationship, Hubble determined a distance of 698,000 light-years. This was the first system beyond the Magellanic Clouds to have its distance determined.

Hubble's distance to this galaxy was way beyond Harlow Shapley's value of 300,000 light-years for the size of universe. In the paper, Hubble concluded the "Great Debate" of 1920 between Heber Curtis and Shapley over the scale of the universe and the nature of the "spiral nebula". It soon became evident that all spiral nebulae were in fact spiral galaxies far outside our own Milky Way.

In 1977, Paul W. Hodge extended the list of known H II regions in Barnard to 16. Today, there are over 150 of these regions catalogued in Barnard's Galaxy.