A nebula is a giant cloud of dust and gas in space. Some nebulae (more than one nebula) come from the gas and dust thrown out by the explosion of a dying star, such as a supernova. Other nebulae are regions where new stars are beginning to form. For this reason, some nebulae are called "star nurseries." Nebulae exist in the space between the stars-also known as interstellar space. The closest known nebula to Earth is called the Helix Nebula. It is the remnant of a dying star-possibly one like the Sun. It is approximately 700 light-years away from Earth.