Classifications of Objects in Space Part 3: Diffuse and Star-forming Nebulae

Because astronomy is an observation-based science, we need to carefully categorize the objects we see. As we explore the cosmos, we discover that not all objects are the same, and even then, some objects that appear the same at first glance differ greatly in the details. Here, we will be discussing the classifications we give the objects we find.

A nebula is basically a large cloud of gas – in that, there are several different categories that define the type of nebula we are viewing.

Today, I wanted to talk about diffuse nebulae and star-forming nebulae.

A diffuse nebula is basically a nebula with no defined edge. The nebula simply blends into interstellar space. In an attempt to stay away from absolutes it is best to say most nebulae can be described as diffuse nebulae. However, I can’t think of or find a single nebula that isn’t diffuse. Diffuse nebulae are normally comprised of reflection nebulae and emission nebulae. You may occasionally hear the term ‘gaseous nebula’ used to describe a diffuse – this is an inaccurate term and isn’t used in any scientific capacity.

Star-forming nebulae, more properly referred to as a molecular cloud and sometimes referred to as a stellar nursery, is a nebula where star formation is actively occurring. The Orion Nebula and the Tarantula Nebula are some such examples of stellar nurseries. These nebulae contain some of the youngest stars in existence and are able to reveal the secrets of the first stages of a stars life.

An example of both a star-forming nebula and diffuse nebula. It is NGC 604 (not pictured) and contains more than 200 of the universes youngest stars. The nebula is about 1,500 light-years across and located about 3-million light-years from Earth in the Triangulum constellation (ironically enough, the nebula also resides within the Triangulum Galaxy.

References, sources, and further reading can be found here: http://www.fromquarkstoquasars.com/classifications-of-objects-in-space-part-3-diffuse-and-star-forming-nebulae/