Emerald Robinson: Hi, I'm Emerald Robinson. In this What is video, we're going to take a closer look at nebulae.
The name nebula means cloud in Latin. A nebula is an immense cloud of hydrogen, helium, and astronomical plasma floating in interstellar space, the spaces between solar systems. Astronomical plasma is a mix of electrons and protons that break free from atoms due to intense heat.
A nebula can form in two different ways. When a giant star or white dwarf star explodes in a supernova, the explosion hurls material into space. That matter can gather into a nebula.
Nebulae also form from interstellar medium. Interstellar medium describes the matter that exists between the star systems. Usually interstellar material is spread out over huge distances that can collapse together due to gravitational forces. When enough interstellar medium collapses, a nebula forms.
While some nebula form from exploding stars, the giant clouds also produce new stars. Over millions of years gravity packs the dust and gases within the nebula into smaller and smaller areas, eventually triggering fusion and the creation of a new star.
Scientists define nebulas by type. A planetary nebula develops from a supernova. Despite its name, a planetary nebula has nothing to do with planets. Glowing nebulae produce faint red light when radiation from nearby stars heats hydrogen gas in the cloud.
Reflection nebulae don't produce their own light. Instead, starlight reflects off dust in the cloud as blue light. Dark nebulae don't produce light either; instead they absorb light rather then reflecting it. Dark nebulae appear as patches of darkness in space, blocking the light from stars behind the nebulae.
Astronomers name nebulae after the shapes these giant space clouds resemble. You may have seen pictures of the Horsehead, Cat's Eye, or Crab Nebulae. And those are the facts on nebulae, the graveyards and birthplaces of stars.