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Transcript
A nebula is an interstellar cloud of
dust, hydrogen gas and plasma. It is
the first stage of a star's cycle.
BOOMERANG NEBULA
Originally nebula was a general name for any extended
astronomical object, including galaxies beyond the
Milky Way (some examples of the older usage survive;
for example, the Andromeda Galaxy was referred to as
the Andromeda Nebula before galaxies were
discovered by Edwin Hubble).
Nebulae often develop star-forming regions, such as in
the Eagle Nebula. This nebula is depicted in one of
NASA's most famous images, the "Pillars of Creation".
In these regions the formations of gas, dust and other
materials 'clump' together to form larger masses,
which attract further matter, and eventually will
become big enough to form stars. The remaining
materials are then believed to form planets, and other
planetary system objects.
BUBBLE NEBULA
Many nebula form from
the gravitational collapse
of diffuse gas in the
interstellar medium or
ISM. As the material
collapses under its own
weight, massive stars
may form in the center,
and their ultraviolet
radiation ionises the
surrounding gas, making
it visible at optical
wavelengths. An example
of this type of nebula is
the Rosette Nebula.
PELICAN NEBULA
The size of these
nebulae, known as
HII regions, varies
depending on the
size of the original
cloud of gas, and the
number of stars
formed can vary too.
As the sites of star
formation, the
formed stars are
sometimes known
as a young, loose
cluster.
CASSIOPEIAA NEBULA
Some nebulae are formed as the result of supernova
explosions, the death throes of massive, short-lived
stars. The material thrown off from the supernova
explosion is ionised by the supernova remnant. One of
the best examples of this is the Crab Nebula, in Taurus.
It is the result of a recorded supernova in the year 1054
and at the centre of the nebula is a neutron star, created
during the explosion.
Other nebulae may form as
planetary nebulae. This is the
final stage of a low-mass star's
life, like Earth's Sun. Stars with a
mass up to 8-10 solar masses
evolve into red giants and slowly
lose their outer layers during
pulsations in their atmospheres.
When a star has lost a sufficient
amount of material, its
temperature increases and the
ultraviolet radiation it emits is
capable of ionizing the
surrounding nebula that it has
thrown off.
CATS EYE
NEBULA
A planetary nebula is an astronomical object consisting
of a glowing shell of gas and plasma formed by certain
types of stars at the end of their lives. The name
originates from a similarity in appearance to giant
planets when viewed through a small optical telescope
and is unrelated to planets of the solar system. They are
a relatively short-lived phenomenon, lasting a few tens
of thousands of years, compared to a typical stellar
lifetime of several billion years.
Most nebulae can be
described as diffuse
nebulae, which
means that they are
extended and
contain no welldefined boundaries.
In visible light these
nebulae may be
divided into emission
nebulae and
reflection nebulae, a
categorization that
depends on how the
light we see is
created.
EMISSION
NEBULA
REFLECTION
NEBULA
Emission nebulae contain ionized gas (mostly ionized
hydrogen) that produces spectral line emission. These
emission nebulae are often called HII regions; the term
"HII" is used in professional astronomy to refer to ionized
hydrogen. In contrast to emission nebulae, reflection
nebulae do not produce significant amounts of visible
light by themselves but instead reflect light from nearby
stars.
The Flame Nebula is part of the
Orion Molecular Cloud Complex and
is an emission nebula.
HORSEHEAD NEBULA
Dark nebulae are
similar to diffuse
nebulae, but they
are not seen by
their emitted or
reflected light.
Instead, they are
seen as dark
clouds in front of
more distant stars
or in front of
emission
nebulae.
Planetary nebulae are so called because the first
astronomers who observed these objects thought that
the nebulae resembled the disks of planets, although
they are not at all related to planets.
A protoplanetary
nebula (PPN) is an
astronomical object
which is at the shortlived episode during a
star's rapid stellar
evolution.
A supernova occurs when a high-mass star reaches
the end of its life. When nuclear fusion ceases in the
core of the star, the star collapses inward on itself.
The gas falling inward either rebounds or gets so
strongly heated that it expands outwards from the
core, thus causing the star to explode.
CRAB
NEBULA
Now let’s sit back and gaze upon a variety of
nebulae …
CHRISTMAS
TREE NEBULA
CONE NEBULA
CRESCENT NEBULA
EGG NEBULA
HELIX NEBULA
ESKIMO NEBULA
I C 2924
INTERSTELLAR
CLUSTER 1396
LAGOON NEBULA
MESSIER 20
MZ3
NEAR GALAXY
CLUSTER 346
M 29
Travels the
spaceways
feeding upon
planets and
enjoys the
occasional
nebula desert.
These two don’t often get along.
Until next time…