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The Universe
What is It?
The Universe is the entire of what we would call 'space'. It includes earth, the sun, all of
the stars you can see at night, plus many more you can't and all of the planets that
float around these stars.
The universe is made up of galaxies. These are clumps of stars, planets, gas and dust
that are held together by gravity. The galaxy that we are in is called the 'Milky Way';
most scientists believe it is held together by the gravity of a black hole (a very small
star). Galaxy come in various shapes and sizes, our galaxy is a spiral shape.
To get an idea of the size of the universe. The milky way is 180 000 light years across,
meaning it would take 180 000 years to travel from one side the other at the speed of
light. And there are billions of galaxies in the observable universe, possibly billions
more outside of the area we can see.
Big Bang Theory
This is probably one of the most famous scientific discoveries, but it is an everyday
phrase that people use without really knowing what it means.
The theory that is more or less the one we use today was proposed by someone who
doesn't get a lot of attention in the popular press. He was a Catholic Priest from
Belgium called Georges Lemaître and put forward the theory in 1931.
The theory says that the universe began as a very small particle consisting of the
entire universe squashed together. This particle then 'exploded', and when an
explosion happens it pushes outwards (think of movies). This caused the universe to
expand and it is believed that the universe continues to expand.
This expansion means that these galaxies mentioned above are moving away from
each other. And this has been observed by astronomers; providing evidence for this
theory.
Further evidence for the Big Bang is background radiation. Background radiation is
the low levels of radiation that exist all around us; this radiation is picked up by an
analogue television to produce 'snow' when it is not tuned. Background radiation in the
universe is said to be left-over heat energy from the initial explosion of the universe.
Future of the Universe
If the universe is expanding, it means it has been possible for scientists to work out
what might be the fate of the universe. However it depends upon the mass of the
universe.
A common theory is that of the big crunch this will happen if the universe is above a
critical mass. It says the universe will eventually stop expanding and then compact
again. As it does this getting hotter. It will eventually compact into a single particle like
at the beginning of the Big Bang Theory; many say that the universe will then be
'reborn' with another big bang and continue expanding and contracting forever.
Another possibility is if the mass is too low, in which case the universe will continue to
expand forever, getting colder and colder as it does so; until it is eventually virtually
empty and frozen.
Our Solar System
The solar system includes everything that orbits our sun. As well as the 8 planets, there
are asteroids, comets and, dwarf planets. The image below shows planets in their
order from the sun. This is not to scale but the relative sizes of each planet is accurate
if you double the gas giants diameters.
The first four planets are known as terrestrial planets. They have common
characteristics such as they are all rocky and do not have rings. The last four planets
are known as gas giants these planets are all very large and have rings.
Also in the solar system is the asteroid belt this is an area between Mars and Jupiter
that contains many thousands of asteroids. Asteroids are large pieces of rock, ice and
metal that altogether are estimated to be 4% the weight of our moon.
Also floating around the solar system are Dwarf Planets. This is a new classification
that was introduced in 2006. There are 3 dwarf planets in our solar system. One
(Ceres) is in the asteroid belt. Then there is Pluto, which was a planet for almost 80
years before being reclassified, and finally Eris, which is even further out of the solar
system than Pluto is.
Solar System Formation
Everything has a beginning, and our story begins when the cloud that
was the Solar Nebula began to contract. All stars exist in islands
called galaxies, and galaxies contain old and new stars as well as
clumps of dust clouds. These clouds contain mostly hydrogen and
some heavier metals (any elements that are heavier than helium is
considered a metal by Astronomers). As we will learn the Sun
section, stars create their energy by a process called fusion. When a
star ends its life, it explodes in a tremendous phenomenon called a
supernova. A supernova has so much energy that heavy metals are
formed - metals like iron and gold. These elements "seed"
surrounding hydrogen clouds so that newer stars will contain more
heavy elements in their atmospheres.
It is believed that for a system of planets to form around a star
during cloud contraction the cloud must contain heavy elements.
The image below demonstrates how our Solar System was formed:
For the cloud to begin contraction, two conditions must be met:
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Jean's Mass - the cloud must contain a certain amount of mass
that depends on...
Jean's Length - if the cloud of a certain mass is also a certain
diameter, contraction will begin
Click the image on the left for a video
of a simulated formation of a system
of planets.
This particular simulation
demonstrates the Solar Nebula
Hypothesis - the formation of our
Solar System (video care of
Swinburne Astronomy Online).
Jean's Mass and Jean's Length are an advanced type of Stellar
Astrophysics that will not be covered here, but a simple definition is
that when a cloud contains a certain amount of debris and is a certain
size, the likelihood of cloud contraction is high. But if a cloud exists
happily at a certain size, how can it begin contraction? The answer is
outside influence:
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Surrounding supernova can generate shockwaves that will
affect the debris in a nearby cloud - if the cloud is shocked
enough and debris is forced inward, contraction can begin
The natural rotation of the galaxy can slowly affect the
structure of a cloud
Density Waves - a theory that explains the spiral structure of
galaxies - can also stimulate these clouds
This image from the Hubble Space
Telescope shows a solar nebula, evidence
to support the Solar Nebula theory. This is
called a protoplanetary disk, or proplyd. This
proplyd lies at the heart of the Orion Nebula
along with dozens of other proplyds. The
darker area is the dense molecular cloud
while the proto-star (a star that is hot, but
not hot enough to initiate fusion) is the glow
in the center.
While the above image shows the early stages of a system of planets,
there are stars that already have formed planetesimals. The image
below is of Beta Pictoris:
This image clearly shows that this star has 4 distinct rings. These
rings will eventually coalesce into solid bodies called planets.
Our Solar System has three distinct features as a direct result of its
formation:
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The Terrestrial Planets (Mercury, Venus, Earth and Mars)
The Asteroid Belt
The Gas Giants (Jupiter, Saturn, Uranus and Neptune)
During formation, these bodies that would form planets