SCIM1040 Lecture Notes - Lecture 2: Light-Year, Barred Spiral Galaxy, Large Magellanic Cloud

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SCIM1040-Lecutre 2
The Universe and its Energy
(Earth and Space, Physical World)
What is the Universe?
The total sum of all matter and energy. i.e., everything within and between all galaxies.
Recent data analysis has found that the universe is considered to be about 13.8 billion
years old.
The universe is unbelievably enormous
Viewing the Universe is looking back in time
When you look at the blue star Rigel in the constellation Orion at night (the upper left of
the constellation), you really see it as it was about 900 years ago because its light has
taken up to 900 years to reach Earth. The way you see it tonight is actually what it looked
like all that time ago.
Today it could come to the end of its existence in a spectacular supernova explosion but
you will have to wait 900 years before you can witness this brilliant event.
Distant Galaxies of the Universe
Each dot indicates the position of a galaxy six billion years into the past. The image covers 5% of
the sky, a slice of the universe six billion light-years wide, 4.5 billion light-years high, and 500
million light-years thick. Colour indicates distance from Earth, ranging from yellow (nearer) to
purple (further). This image contains 48,741 galaxies, about 3% of the full survey dataset.
Components of the Universe
Our Universe is only about 5% ordinary matter (gas, stars, planets, dust, etc).
Dark matter accounts for the vast majority of mass in the Universe. Dark matter is a
substance that exists but it is not visible. It is belieed to e like glue holdig the galaies
together especially as they rapidly spin.
Astronomers can only see the effects of its gravity in influencing how galaxies rotate and
how clusters of galaxies behave. There is more than five times as much of dark matter as
there is normal matter.
Dark energy is necessary to account for the fact that the universe is apparently not just
expanding but accelerating at an ever-faster pace.
What as the Big Bag?
The Big Bang is a scientific theory based on observations that other galaxies are moving
away from each other at great speed, in all directions, as if they had all been propelled by
an ancient explosive force. Technically, the galaxies are not moving, space is expanding.
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So, it is often described as a cosmi eplosio of atte ithout a ag that aused the
birth of the universe resulting in the expansion and cooling of the early hot, dense
universe and the clumping of matter to form billions of galaxies each consisting of billions
of stars.
What is the ultimate fate of the Universe?
Astooes eliee that the Uieses epasio is aeleatig ad it ill go o epadig,
getting larger and larger, and colder and colder. Perhaps, the Universe will eventually end in a Big
Chill (or Big Freeze) resulting in it being too cold to support any life.
Redshift: Evidence for the Big Bang
Redshift - If a galaxy or star is moving away from an observer, then redshift occurs. This means
that the light waves from the galaxy or star have become stretched, i.e., the wavelength of the
light wave (distance between two crests or two troughs) has become longer.
* Redshift from distant light sources in the universe is one kind of evidence for the expansion of
the universe. Galaxies and stars appear redder as they speed away.
Blueshift In comparison, if a galaxy or star is moving towards us then blueshift occurs because
the light waves have become bunched closer together.
Have you noticed how the horn of a moving train or the siren of an ambulance or fire
engine changes pitch? As it nears you, the pitch appears to become higher but as it goes
away from you, the pitch appears to get lower.
In fact, the pitch has not changed at all. The effect occurs because the sound waves arrive
at the listees ea lose togethe as the source approaches, and become further apart as
the source of the sound move away.
This pheoeo is alled the Dopple Effet o Dopple “hift ut he it is applied to
light it is called redshift and blueshift.
Features of galaxies
About 100-500 billion galaxies may exist in the Universe.
Each galaxy contains billions of stars, gas and dust, yet a galaxy is mainly empty space.
Galaxies vary in size and shape.
Our SUN is a part of the Milky Way galaxy located on the Orion spur about 26 000 light
years from the galaxy centre.
What are stars?
Stars are created in clouds of dust and gas called nebulae. Not every nebula will give rise
to stars.
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Stars are large balls of hot gas.
Stars look small because they are very distant, but in fact many are bigger and brighter
than the Sun.
Our Sun looks large only because it is so close.
There are different colours and sizes of stars with different temperatures and brightness.
There are about 1000 stars in the universe for every grain of sand on Earth.
Temperature and Colour of Stars
Stars vary in temperature. The range of colours stars emit depends on their surface
temperature.
Cooler surface temperatures (below 39000C) result in a red colouring.
Hotter temperatures change the colour to orange, then yellow (our Sun, at about 60000C),
and then white and blue.
Blue stars are the hottest stars.
The hotter a star is, the shorter the life of the star.
Types of galaxies
1. Many galaxies are spiral i shape, hae a ulge i the iddle ith to o oe as
making them look like UFOs or fried eggs when viewed from the side. 1a is a typical barred
spiral galaxy similar to our Milky Way.
2. Some galaxies look like bright footballs in space (elliptical).
3. Some galaxies do not have any special shape (irregular).
Examples of spiral galaxies
Andromeda 2.2 Mly away (nearest large galaxy to our own)
Mly = million light years
1 light year is a unit of distance and is the distance light travels in one year at the speed of 300
000km/s
Whirlpool 23 Mly away
1 ly= 300 000 x 60 (secs in 1 min) x 60 (mins in 1hr) x 24 (hrs in 1 day) x 365.25 days in 1 yr) =
approx. 10 trillion km
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Document Summary

The universe and its energy (earth and space, physical world) The total sum of all matter and energy. i. e. , everything within and between all galaxies: recent data analysis has found that the universe is considered to be about 13. 8 billion years old. The way you see it tonight is actually what it looked like all that time ago. Today it could come to the end of its existence in a spectacular supernova explosion but you will have to wait 900 years before you can witness this brilliant event. Each dot indicates the position of a galaxy six billion years into the past. The image covers 5% of the sky, a slice of the universe six billion light-years wide, 4. 5 billion light-years high, and 500 million light-years thick. Colour indicates distance from earth, ranging from yellow (nearer) to purple (further). This image contains 48,741 galaxies, about 3% of the full survey dataset.

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