Unit 8 Astronomy

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Unit 8 Astronomy!!!

• Chapter 27 Stars and Galaxies
• Chapter 28 The Sun
• Chapter 29 The Solar System
• Chapter 30 Moons, Rings and Things

Galactic Cannibalism
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Who are we?Where are we?Why are we here?
We humans are small beings, living on a small
planet, revolving around a below-average sized
(and rather dim) star, which is only one of 400
billion other stars in a medium-sized galaxy.
Just one galaxy of billions of others in a vast
universe. So, what makes us so special?
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• To our present knowledge, we are alone
• Or are we?
• No other star out there has a goldilocks
  planet? None???
• Doubt it!!!

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Why do stars twinkle?
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Star of the Show
Size

• STAR A body of gases which gives off light and
  heat
• Look at the sky at night and notice the various
  color of the stars!
• Color temperature
• Stars also vary in vastly in size, density and
  mass.

Temperature
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Orion The Hunter
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All from a tiny
speck of light?
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More on light

• Spectroscope ?
• Spectra types
• Continuous
• Bright-line
• Absorption

These three types of spectra tell us temperature
and composition of stars. All stars are made
mostly of hydrogen (1st) and helium (2nd) but
they also have other elements that can be seen by
using their spectra.
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Oh and telescopes dont make stars look bigger!
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Motion of Stars
Apparent motion Motion of stars due to the
rotation of Earth on axis
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Actual Star Motion(relative to other stars)

• Stars have 3 actual motions
• They rotate on an axis
• They can revolve around another star
• They move away or toward Earth (Doppler Effect)
• Red shift
• Blue shift

This is called proper motion
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Big Dipper in 10,000 years(as seen from Earth)
Movement due to proper motion
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One More Star Motion

• Stars shift toward the west every night (rise 4
  minutes later each night) eventually giving us
  a different view of our galaxy throughout the
  year facing outward in our orbit.
• Slowly setting thru the weeks and months
• Different constellations
• Zodiac

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QC Circumpolar Stars
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Distances to the Stars

• Measuring distance in space could be accomplished
  by using miles and kilometers.
• But, talk about huge numbers!!!
• The Sun is (take your pick)
• 93 million miles away
• 150 million kilometers away
• 1 Astronomical Unit (AU) away
• 8 light-minutes away
• The Moon is the distance of one light-second from
  Earth.

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Tools for Determining Distance
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The Light-Year

• The distance that light travels in 1 year
• Light travels 300,000 km/sec
• Therefore the Moon is one light-second from Earth
• One light-year is almost 10 trillion kilometers!
• The l.y. is a rather small distance in the
  astronomical scale.
• Parsec 3.26 light-years

Meet your neighbors
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Parallax
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3
1
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4
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• This is what enables you to hit a baseball with a
  bat
• Your eyes (which see in stereo) and brain work
  together to interpret distances to things
• Deer dont have it neither do children under age
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• ? is the parallax angle, but what is THAT?
• This angle allows us to use a little geometry
  (trig) to determine distances to objects almost
  anywhere
• Index finger 3o
• Parallax (in space)

January
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Cepheid Variable Stars

• Determining the brightness of a star is a science
  in and of itself
• Many ways to do this
• But using a special kind of star helps us find
  distance to it (or its galaxy).
• Longer cycles are brighter

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Can you tell which is the Cepheid variable star?
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Stellar Magnitudes

• 6,000 seen from Earth with naked eye
• Most of the 3 billion that can be seen from
  telescopes are too faint
• Visibility depends on two things
• Brightness
• Distance from Earth
• Absolute magnitude
• Apparent magnitude (scale) Notice lower numbers
  are bright

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Which have the biggest apparent magnitudes?
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Absolute Magnitude

• Puts all stars 10 parsecs or 32.6 light-years
  away from Earth to compare brightness
• The Sun would barely be visible from Earth at
  this distance at 5 mag
• Stars closer to Earth than 10 parsecs are
  brighter b/c of their closeness so their
  apparent magnitudes are lower numbers (seem
  brighter) than their absolute numbers (how bright
  they really are)

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• You are an alien from another planet and drop in
  on Earth. You cannot speak, but have excellent
  observational skills. You know nothing about
  Humans, but want to find out how they age or
  how they progress through their life stages.
• How could you figure it out in a one-day visit?

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Classification of Stars
Super-giants Giants Main-Sequence stars Dwarfs
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Stellar Evolution and Death
Nebula
Sun-like stars
Massive stars
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Nebulae

• All stars begin as a dust and gas cloud
• In fact, very atom in your body came from star
  dust!
• A nebulae can form more than one star
• Within the cloud, particles eventually stick and
  gravity does the rest
• Gravity causes it to shrink, rotation speeds up
  and temps rise
• Eventually, forming a disk of matter with a hot
  protostar or baby star - in the middle

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Orion Nebula
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A Star is Born

• Again as more gas and dust accumulate, gravity
  increases
• Gravity pulls material inward, which causes the
  temp and pressure to increase
• Gas turns to plasma
• At 10,000,000o C nuclear fusion begins in the
  core of the new star
• Now---it is officially a star, a main sequence
  star---where it will spend most of its life

A protostar
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Main Sequence Starsare doing E mc2 ?

• You dont have to go far to find a main sequence
  type star our Sun!
• Fusion pushes outward gravity pulls inward.
  Makes the star stable in size
• Will burn hydrogen in the core until its fused
  into helium

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And on to the giants

• Hydrogen core is no longer burning and pushing
  outward, so gravity pulls it in
• Helium core begins to burn and fuse into carbon
• Hydrogen burning shell and helium burning -
  together these release energy
• Expand and cool over bigger volume- thus turning
  red
• Red supergiant (100 x Sun) or giant (10 x Sun)

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Until now, the evolution of all stars is
basically the same, until their death
Nebula
Sun-like stars
Massive stars
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The Remnants of Sun-like Stars
White Dwarfs and Planetary Nebulae
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Nova in Aquila (the eagle)
Novas are short-lived star explosions usually
only 1 to 3 days in length. Can be a single white
dwarf or a white dwarf orbiting another star
where material expels and lands on the wd (1
million X)
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Supernovas!!!
Remnants of super-massive stars Live hard die
hard
Supernova eta-carinae
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In 1054 AD, the Chinese and some Native American
tribes noticed a huge explosion in the sky. For 3
weeks, it was brighter than a full moon during
the day! What they had witnessed was a supernova
a massive star that had exploded into space.
Crab Nebula in Taurus
A leftover gas cloud from 1054 that we can still
see!
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More on supernovas

• Cores of these massive stars are fusing into
  carbon during the red giant stage
• Then successively fuse into heavier elements
• Until core is mostly iron
• 90 of matter explodes into space (nebula)
• Remaining 10 core collapses into either
• Neutron star
• Pulsar
• 2. Black Hole
• Depends on the original mass of the star

Supernova 1987A
160,000 light years from Earth
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Neutron Stars

• Leftover core of supernovae
• Rotate quickly
• Must be very small
• Very dense
• Why is it called a neutron star?
• Some neutron stars give off radiation

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Pulsars

• A sub-type of neutron star with 2 sweeping beams
  of energy
• All emit radio waves
• 3 emit wavelengths in the visible realm
• One of these is in the Crab Nebula
• Rotates 33 times a second!!!!!!

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Black Holes!
Umm couldnt find a picture of one of these!
I wonder why? ?
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More in black holes

• The remnant of the most massive of stars
• It is a type of star with a mass that becomes
  bigger and bigger from its insatiable appetite.
• The original core is too big to become a neutron
  star
• The core collapses in on itself and no known
  force is able to stop the collapse
• Density is immense where even the particles of
  light cant escape
• So, where are they?

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Star Groups
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Constellations

• The stars positions relative to each other dont
  seem to change over time
• 88 patterns in the sky
• These constellations map the celestial sphere or
  sky
• A star has to belong to one or another
• You may have noticed that they look nothing like
  their namesakes ?
• Each star is named by brightness within the
  constellation
• Im a Leo, but I cant see Leo in July.

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Galaxies
Average size 100 billion stars and 100,000 l.y.
across 50 billion to 1 trillion galaxies in
universe
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Solar System
Distance from Earth to Sun
93,000,000 miles 8 light-minutes
Size of Solar System 5.5 light-hours
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Stellar Region
Sun (solar system too small to be seen on this
scale)
30 light-years
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What is a Galaxy?
Galaxy
Suns Stellar Region
a massive collection of stars, gas, and dust
kept together by gravity
200,000 light-years
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If our solar system was the size of a cell
in the human body, our galaxy would still measure
over one mile across.
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Spiral
disk-like appearance with arms of stars and
dust forming a spiral pattern
Barred Spiral
similar to spirals but with a bright bar of
stars and gas through the center
Elliptical
elliptically-shaped, with less gas and dust
than spirals no disk or arms
Irregular
neither elliptical nor spiral in shape gas
and dust as in spirals but no defined arms
Peculiar
distorted form of one of the above types,
often due to collision with another galaxy or
similar catastrophic event
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Star Clusters
Open Clusters open, irregular shape, fewer
stars, located in arms of the MW disk
Globular Clusters spherical, many stars, around
central core of MW galaxy
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BANG!!!
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How did the universe begin?

• Big Bang Theory
• 12 to 15 billion years old
• This singularity (all energy) exploded and the
  universe was born in a fraction of a second 10
  43 seconds!!!
• The explosion occurred in all places at the same
  time!
• All matter and gravity in the universe was zero
• Therefore something (the universe) did come from
  nothing (pre-universe)
• Oldest objects in the universe quasars

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