Page 25 - Life beyond the Karman

Where are nebulae?
Nebulae exist in the space between the stars, also known as interstellar space.
Scientists have so far identified five types of nebulae, namely:
a. Planetary nebulae;
b. Emission nebulae;
c. Reflection nebulae;
d. Dark nebulae; and
e. Supernova remnants.
Numerous nebulae are grouped into each of these five categories.
Nebulae vary for numerous reasons, explained below.
Planetary Nebulae
Interestingly, planetary nebulae have almost nothing to do with planets or exoplanets. Instead, they consist of a glowing and expanding shell of gas, ejected from red giant stars late in their lives. Planetary nebulae possess a ring-like shape from this emission of gas. They look like planets due to their round shape.
Emission Nebulae
An emission nebula is unique in that it shines with its own source of light. It is a nebula composed of ionized gases that emit light at various wavelengths. The most common cause of ionization is high-energy ultraviolet photons emitted by a nearby hot star.
Emission nebulae tend to emit a reddish colour because of their abundance of hydrogen.
Reflection Nebulae
Like an emission nebula, reflection nebulae shine through the darkness of space, just not with their own light. True to its name, a reflection nebula does not create its own light but instead shines by reflecting the light of nearby stars. Reflection nebulae are created when the energy from a nearby star is insufficient to create an emission nebula, but is enough to make the dust visible.
Dark Nebulae
The most mysterious of all nebulae are dark nebulae. These unique nebulae are so dense in gas that they obscure visible wavelengths of light, meaning that we are unable to see them and explain why they are also called absorption nebulae. Because of this absorption, to us, dark nebulae just look like dark masses blotting out the stars of space.
Below are some world-famous nebulae:
The Orion Nebula, which is about 1,500 light-years from us. It exists in the Orion constellation.
The Horsehead Nebula is one of the largest to have been discovered in outer space.
The largest nebula, called the Tarantula Nebula, is 1,800 light- years in size at its widest span, and is located at a distance of around 170,000 light-years from our planet.
The Helix Nebula is the closest nebula to the Earth. It is the remnant of a dying star and is approximately 700 light-years from Earth.
There are numerous new nebulae names depending on shape and discoveries as part of ongoing studies on space and the universe.
LIFE BEYOND THE KÁRMÁN LINE - OUTER SPACE
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