Nebulas+in+General

This page was made by Lauryn Fox, for Mr. Adkin's, Astronomy 10 class at Los Medanos College. I am studying what and how nebulas work, as well as the different types of Nebulas: Emission, Reflection and Dark Nebulas. ** EMISSION NEBULA ** Before we get started I will briefly show as well as tell you about 3 different types of nebula. I will first start with __**Emission Nebulas**__; they are clouds of ionized gas (i.e. plasma) that emit light in various colors. The most common source for ionizating are high-energy photons emmitted from a nearby hot star. There are several different types of emission nebula such as H II regions, in which star formation is taking place and young, massive stars are the source of the photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them. Here is a photo of what Emission Nebulae look like: [] | **Fusion Energy Education** This site about Emission Nebula's tells us about the different regions of the emission nebulae, the HII region that's mostly made up of plasma from the ionized hydrogen and electrons. It also tells us about how only very young, hot stars have enough radiation to ionize the hydrogen. When the ions get to lower energy, after they recombine with electrons they let out their characteristic trait of their spectral lines. These lines have a very noticeable red glow, and I learned about the existing "forbidden lines" that you can't see in earth-bound laboratories, these lines are green from the doubly ionized oxygen that gives the nebula that kind of shading. This site also tells us about the most famous and most colorful nebulae that are located in the Northern Hemisphere, they have distinct bright rings and small dark clouds on the brightest parts of the nebulae.

[] | **Reference Answers: Emission Nebula** I found this site to be very imformative, it gives the definition of what exactly the emission nebula is, as well as giving general information about the color and how it depends on it's chemical composition and the degree of ionization. It also tells us how most of the young stars in the cluster do most of the work in this type of nebulae. And when there is more energy available, there is possibility the other elements being ionized will turn to green or blue.

**REFLECTION NEBULA ** Next I will tell you about **__Reflection Nebulas,__ they are clouds ** of dust that are simply reflecting the light of a nearby star or stars. Edwin Hubble distinguished the difference bbetween the emission and reflection nebulae in 1922. The energy from the nearby star, or stars, is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Now here is a photo of a reflection nebula: [] | **NASA Astronomy Picture of the Day; Reflection Nebulae** This site has different photos from different missions with explanation of what each photo is. There is a photo of The Witch Head Nebula that is associated with a star in the Orion constellation called Rigel. This Witch Head Nebula gets in glow directly from the reflection of the light that the star Rigel emits. The super thin dust in the nebula reflects the light which makes it glow. This nebula is 1000 light-years away with a a blue color because of the reflection from the dust grains. This site also goes on to tell us about how "the brightness of the nebula is determined by the size and density of the reflecting grains, and by the color and brightness of the neighboring star(s)." Which I found very interesting.

[] | **Cosmos, The SAO Encyclopedia of Astronomy** This links explains in better detail and in simpiler terms why the reflection nebula has a blue color to it. It tells us that it is created from the light of another surrounding star being reflected off a nearby dust cloud. This light has a similar spectrum to that of the illuminating star, but with a bluer color to it. Therefore the bluer light is scattered throughout more than longer with the red wavelengths giving the blue characteristic for this nebula. Another interesting fact that this site gives us, is how the size of this kind of nebula is not determined by the size of the dust cloud but the area of the brightness that it covers.

**DARK NEBULA ** Lastly but certainly not least, a __**Dark Nebula**__ is a type of interstellar cloud that is so dense that it obscures the light from the background of a emission or reflection nebulae or that it blocks out background stars. The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok Nebulas. Like other interstellar dust/material, things it obscures are only visible using radio waves and radio astronomy. A Dark nebulae looks like this: [] | **Dark Nebula** This site gives more than enough information about dark nebulas. It begins by telling us that these clumps of clouds are very irregular. The largest type is visibile to us looking like dark patches in the middle of the milky way. They sometimes have snake like shapes and don't have clearly defined boundaries. The giant molecular clouds, are more than a million times as massive as the Sun with the smalles of 1 light-year wide. The clouds are contained of mainly gas and dust but most importantly stars. The physical features that I learned about from this site are that the outer parts of the dark cloud, the hydrogen is neutral. Deeper within it, as dust blocks out an increasing amount of stellar ultraviolet radiation, the cloud becomes darker and colder. In the inner regions of dark nebulae important events take place: the formation of stars. Which it goes onto explaining that into simple terms that I can even understand.

[] | <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">**Nebulae** This site really just informs us in general what a nebula is as well as all the different types of them. In pre-telescopic times the word "nebula" was used to distinguish objects which look non-stellar from the pointlike stars. Now it said to mean "deepsky object." It tells us how absortion and dark nebulas are somewhat the same in how they both absorb light, when the gas component is seen as the absorption spectra in the light of the backround stars, as the dust abosrbs and redens the backround light at times.

<span style="color: #000080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;"> Heres a YouTube video that shows all different types of nebulae: <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;"> [] | Tour of Our Galaxy's Visible Nebulae