Transcript Milky Way - mrbemrose

Beyond our Solar System
The Milky Way
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Our solar system is part
of a galaxy called the
Milky Way
The Milky Way contains
about 400 billion stars!
It appears as a hazy
white band spanning from
the southern horizon
across the sky overhead
It is approximately
100 000 light years
across
What is a Galaxy?
A Galaxy is…
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A huge collection of gas,
dust, and hundreds of
billions of stars
They are held together by
gravity
Galaxies have been
moving away from each
other since the BIG
BANG!
Three Types: Spiral,
Elliptical or irregular
Spiral Galaxies
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The milky way
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Arms spiral outwards
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Nuclear bulge at centre
Elliptical Galaxies
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These are the most
common galaxies
Most are shaped like
a football
Stars wrap around the
centre in all directions
“Giant Elliptical”
Galaxies can hold 1
trillion stars and are 1
million light yrs across
Irregular Galaxies
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These galaxies have
no fixed shape
Stars, gas and dust
are spread randomly
They are the smallest
and are seen as
building blocks for
larger galaxies
What is a Nebula?
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The Famous Eagle Nebula
Suns and planets are
still forming within
galaxies in areas
called nebulas
Nebulas are vast
clouds of gas and
dust (more on this
later!)
The Orion Nebula
The Horse Head Nebula
How many galaxies are out there?
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In 1925, Edwin Hubble
realized a “nebula” he
was looking at was
actually an entire galaxy!
We now believe that
there are about 400
billion galaxies!
The Hubble Space
Telescope (HST) was
named in his honour.
Hubble ST Deep Space Field
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This image covers a
speck of sky
equivalent to the
width of a dime held
75 feet away
There are 1 500
galaxies visible in this
photo!
You do the math!
The Formation of the Universe
The Big Bang Theory
The Big Bang
This is the most widely accepted scientific
explanation for the origin of the universe.
According to this theory…
 The universe began in an instantaneous
event that occurred ~15 billion years ago
 When the “clock started”, there were no
galaxies at time zero, not even atoms!
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The Big Bang
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The universe started
out very small and
dense, and is
expanding as it cools
As the universe
cooled, quarks
combined to form the
sub-atomic particles
(p+, e-, n)
Atoms were then
formed
The Big Bang
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“Light’ atoms (He, H,
Li, Deuterium) were
produced by the
young, hot universe.
Later, “heavy” atoms
were formed by the
nuclear reactions that
power stars.
The Big Bang
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http://www.youtube.com/watch?v=PV0ACI
ykxQI
Movement of the Stars
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The stars do not
move across our
sky…they just appear
to because the earth
is rotating on it’s axis
Polaris – The North Star
Polaris – The North Star
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The axis of the earth
is in line with the
North star, so this star
does not appear to
move at all.
All other
constellations near it
appear to revolve
around the “pole” star
Movement of the Stars
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Stars are moving
however, within their
own galaxies, since
all galaxies are
moving away from
each other as the
universe keeps
expanding
Is it a Star or a Planet?
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Stars “Twinkle” and
“move” through the sky
as part of a constellation
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Planets emit steady light
(reflected from the sun)
They “wander” through
the constellations near
the “Ecliptic Line”
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