Aloha, welcome to Learn the Sky. My name is Janine and in this video we're
going to review the types of nebulae that exist. A nebula is defined as a
cloud of gas and dust that consists mostly of hydrogen. Typically there are
other trace elements that exist within the cloud, such as water, formaldehyde,
alcohol, and other trace elements, but they mostly consists of hydrogen. Now
before we dive into the different types of nebulae let's go over the singular
and plural versions of this word, just so there's no confusion. So when we talk
about a nebula that's when we're looking at one specific nebula. So that's a
singular version of this word, but if we say nebulae that means that is plural, so
more than one nebula we say nebulae. There are five main types of nebulae and
they can be broken down into two categories, the ones listed at the top
such as absorption, reflection, and emission these are known to be diffuse
nebulae, so they do not have the definitive shape, in fact they're often
named after objects that they resemble. The other types of nebulae include
planetary nebulae and supernova remnants, and the shape of these nebulae are
typically spherical in structure. Now let's review, and take a look at what
these different types of nebulae look like. So our first one that we're going
to examine is called an absorption nebula, and the way this one works is
that it is such a dense dark cloud that light cannot pass through it. It almost
absorbs that light that is passing through it, and the classic example of an
absorption nebula is the Horsehead Nebula, which is located
in Orion, right near the belt and sword, and as you can see there's no definitive
shape, it's not spherical, it can be considered to be asymmetrical, but many
nebulae are named after what they resemble and if you take a look at this
you can sort of see how it would resemble a horse's head. Another classic
example of a Dark Nebula ,or absorption nebula, is a snake nebula, and this one is
located in the constellation called Ophiuchus, and you can just see here that
this cloud of gas and dust is just so thick that light cannot pass through it.
The next type of nebula is called an emission nebula, and these are clouds of
gas and dust that are glowing brightly due to fluorescence. So inside this cloud
of gas and dust there are tiny stars that are starting to be born, and what
this does is it heats up the cloud and it causes it to glow, and the Orion
Nebula in the constellation of Orion is a classic example of an emission nebula,
and where would you find this? If you would look at the belt stars of Orion
right here, the Orion Nebula sits right in his sword, and there are other
spectacular nebula right around the belt stars as well, in fact this is where the
Horsehead Nebula is as well. Here are other great examples of emission nebulae.
To the left we have the North America nebula,
this is located in the constellation Cygnus, and as you probably notice it
does resemble a continent of North America, but even cooler on the right is
called the ghost nebula and this is located in the constellation cepheus and
it's just so cool how you have this cloud and inside of it you have a little
baby star and that star is starting to heat up a nebula and it glows, and it
does look ghost-like for sure so again another example of how we are naming
things after what they resemble, and even here these kind of look like little
ghosts coming out as well. The third type of diffuse nebulae ,or irregular shaped
nebulae, would be the reflection type, and this is unique in the sense that it is
illuminated, this cloud of gas and dust is illuminated, by the glow of nearby
stars and typically reflection nebulae are more blue in color because the dust
tends to scatter blue light more effectively than red. So typically these
nebulae are more blue in color, and the Pleiades star cluster, located in the
constellation Taurus, is another classic example of this type of nebulae. This
next nebula I'd like to share with you is called the Trifid nebula, also known
as Messier 20, and this one is very interesting because it is a rare
combination of the three types of diffuse nebulae that exist. So when we're
looking at this picture we're looking towards the center of the Milky Way
galaxy and right through the constellation Sagittarius, so I'm going
to bring your attention to this area, and this is the part of the picture that we
are going to zoom in, and this is what we find. So the Trifid
Nebula shows each type of diffuse nebulae that exist. So the dark portions,
all right in here, that is considered an absorption nebulae, or a dark nebula, and
then the pink areas all throughout here this would be considered to be an
emission nebula, and then up here this bluish area is considered to be a
reflection nebula. So again the fact that these are all combined into one type is
very very interesting and this is one of those few spots in the sky that just
definitely attracts many different types of astronomers, because you get to see
three types in one specific astronomical object.
So just to recap so far we have explored the diffuse types of nebula, the ones
that do not have a definitive shape, and those were absorption, reflection, and
emission. Now let's go ahead and look at the types of nebulae that do have a
definitive shape. Our first type of spherical nebulae are the planetary
nebulae, but the name is slightly misleading because these types of
nebulae have nothing to do with planets, and they were first named when William
Herschel in 1785 observed these through a telescope and he thought that they
looked very similar to the spherical shape of a planet. So that's why they
were named planetary nebulae, but in fact this object is really a dying star in
the end stages of its life, and this is eventually what will happen to our Sun.
So this star, right here in the center, is not truly a star anymore because it's
not undergoing fusion. It's run out of hydrogen and helium and all the elements
it was using at one time in its core, and this is all that's left, is this little
white dwarf star, it's the hot leftover core of a main-sequence star,
regular-type star, and these outer layers are the gases that are being blown off
the star, and they really have some beautiful shapes. So this is really at
the end stages of the star, and typically at the end of the red giant phase, and
you have this little white dwarf left in the center. So let's take a look at some
other ones. This is the Eskimo nebula, right here, in Gemini. You can probably
see while it has that name, because it definitely looks like an Eskimo with its
hood up, and then we have the Dumbbell Nebula, this is located in Vulpecula,
which is known as a fox in the southern hemisphere, and if we were to go back to
this one, this is known as the cat's eye nebula in Draco the dragon. The final
type of nebulae that we will examine is called a supernova remnant, and these are
some of the coolest looking nebulae that exist. So how these form is that these
are the leftover remains of a supernova explosion, and you can really just tell
from this picture that this really looks like it was blown to smithereens.
Everything is moving outwards from the center, and typically within these
supernova remnants there are pulsars inside of there, so hot neutron stars
that are spinning very very rapidly and often send out radio signals, and the one
that we're looking at here is called the Crab Nebula, located in Taurus, and let's
take a look at where that would be. So if you have Orion, right down here, and use
the belt stars to help you find the v-shaped face of Taurus, and then you
come down to the lower horn, the Crab Nebula is located right near the tip of
the horn in Taurus the bull. So what's interesting about supernovas is that
this is the celestial event that occurs when all the elements on the
periodic table are created. Regular stars, like our Sun, do not have the ability, or
the mass that they need in order to fuse together higher elements, and the the
largest element that any star could form is iron, and once iron starts to form
inside of the star it becomes unstable, and the iron starts to absorb the energy,
therefore causing it to be unstable, and then kaboom, that's when a supernova
occurs, and this whole shell of clouds and gas and dust is still expanding to
this day, and if you were to look up different types of pictures of super
number supernova remnants they really do have this this spherical, but also
irregular structure and which really just looks like it was blown up. Let's
review the five different types of nebulae that exists, and the two
different categories that they are in. So all the nebulae that are listed at the
top, those are a regular shaped nebulae their diffuse. They do not have a
definitive shape, and if they do have a shape sometimes their name will reflect
that shape like the Horsehead Nebula, which is considered to be a Dark Nebula,
in the sense that it's really absorbing the light that is surrounding it because
the clouds are so thick that light cannot pass through. We also have
reflection nebulae, and these are the ones that are reflecting the light that
are coming from nearby stars. The dust that is located within the cloud is
scattering the light causing that blue color, and then the final diffuse type of
nebula are emission nebulae, and these are ones that are glowing because the
stars that are located inside here are starting to become hot and it causes all
the gas inside to glow, due to fluorescence. Now we have the spherical
type shape, that one would be the planetary nebulae,
and these are the nebulae that are dying, there at the end of their life and
they're just throwing off all the outer layers but they have this very unique,
sometimes almost a series of rings around rings with each other, and even
though they're named planetary nebulae they do not have anything to do with
planets. They just inherited that name because at one time astronomers thought
it looked like a planet, and then finally we have supernova remnants, and these are
violent reactions of a dying star in which pretty much the whole thing was
blown apart, many different elements were created, and it also creates a super cool
shape, and often there are little pulsars inside of here, little neutron stars that
are spinning rapidly and giving off radio stars. Thank you so much for
watching, if you have any other interest about constellation or different types
of celestial objects that exist out there feel free to subscribe to my
channel and I encourage you to keep going outside, observing the stars, and
then as you start to learn the sky share what you have learned with others, and
inspire them to go outside as well. Thanks for watching!