A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any extended astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was referred to as the Andromeda Nebula before galaxies were discovered by Edwin Hubble. Nebulae are often star-forming regions, such as in the Eagle Nebula. This nebula is depicted in one of NASA’s most famous images, the “Pillars of Creation“. In these regions the formations of gas, dust, and other materials “clump” together to form larger masses, which attract further matter, and eventually will become massive enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects.