The Andromeda Galaxy is often referred to as the Great Andromeda Nebula in older texts. Before their nature was understood, galaxies were classified as nebulae, but no longer are. In 1864, William Huggins examined the spectra of about 70 nebulae. He found that roughly a third of them had the absorption spectra of a gas (so these were true nebulae). The rest, including Andromeda, showed a continuous spectrum and thus were thought to consist of a mass of stars.