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Stars

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Stars Temperature Hotter objects emit shorter wavelengths Cooler objects emit longer wavelengths Ex. Sun is a medium hot (5800 K or about 5500 C) star and ... – PowerPoint PPT presentation

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Date added: 5 December 2019
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Title: Stars


1
Stars Temperature
  • Hotter objects emit shorter wavelengths
  • Cooler objects emit longer wavelengths
  • Ex. Sun is a medium hot (5800 K or about 5500
    C) star and emits X-rays
  • Cooler stars emit infrared
  • Determining surface temperature by maximum
    emitted wavelength (Wiens Law)
  • NOTE 0 degrees Celsius 273 Kelvin
  • -273 degrees Celsius 0 Kelvin

2
Stars Color
  • 25,000 K star looks blue
  • 6,000 K star looks yellow (like our sun)
  • 3,000 K star looks red
  • Chemical composition of burning gas
  • Determined by passing light through a prism to
    generate a spectrum
  • Light passed through nebula may have absorption
    lines
  • Ex. Sun is 74 Hydrogen, 25 Helium, 1 Other
  • Spectral Class combination of temperature and
    chemical composition
  • Signified by a letter O, B, A, F, G, K, M
    (hottest to coolest)
  • Our sun is G2

3
Stars Finding Distance by Brightness
  • Why do you think stars would be different
    brightness levels?
  • Apparent Brightness combination of energy
    emitted and distance from Earth, brightness
    decreased by square of distance.
  • Intrinsic Brightness known as LUMINOSITY,
    measured in watts.
  • If you know the apparent and intrinsic
    brightness, you can figure distance.

4
Star Evolution
  • Group 1 Star Formation Birth (11-1)
  • Group 2 Star Energy Helium Fusion
  • Group 3 Stellar Structure and Energy Transport
    (11-3)
  • Group 4 Why is there a Main Sequence?
    (p.262-267)
  • Group 5 Post-Main-Sequence Evolution (12-2)
  • Group 6 Evidence of Evolution Star Clusters
    (12-3)

5
Stars Motion Determined by Light
  • Doppler Effect Motion of a lights source
    affects its observed wavelength of light
  • Approaching observer, waves compressed, shortened
    wavelengths (BLUESHIFT)
  • Moving away from observer, waves spread out,
    lengthened wavelengths (REDSHIFT)
  • Perpendicular motion to observer does not shift
    the wavelength

6
Remember that old commercial?
  • Draw a person or an ear to represent the
    observer.
  • Animations of Doppler Effect

7
EW We are going to be reviewing today for the
final next Monday. Write down what the big
bang theory and evidence for it are.
8
Tuesday, June 3rd, 2014
  • LT I will be able to discuss the big bang
    theory, evidence for it and star life cycles.
  • Agenda
  • -Review for final next week
  • -can use note card on final
  • Tomorrow
  • -Climate Change

9
  • Origins
  • began with a large explosion called the big bang
    theory
  • only energy before this, no matter
  • first hydrogen and helium were formed
  • larger elements were formed later by stars

10
The Big Bang Theory
11
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12
Big Bang Theory
  • Expansion indicates a denser, hotter past
    uniform, hot gas that cools as it expands
  • NOT an explosion from a point, but a simultaneous
    expansion from all places
  • 13.7 billion years ago

13
Big Bang
  • EVIDENCE
  • 1. Cosmic microwave background radiation
    noise, same in all directions
  • 1965 Arno Penzias and Robert Wilson
  • 2. Expansion measured by Hubble constant
  • Distant galaxies are redshifted (based on
    electromagnetic spectrum)
  • This is the doppler effect being applied to light
  • 1929 Edwin Hubble
  • 3. most elements in universe are H and He (light
    elements)
  • Created during first moments of Big Bang
  • when stars reach the end of their life cycle,
    they distribute C, O, and Fe into the universe
  • if the universe was older, there would be more C,
    O, and Fe

14
Expanding Universe
  • All distant galaxies are redshifted. What does
    this mean about their distance from us?
  • Hubble Law further away a galaxy is, the faster
    it is speeding away
  • If we can determine how fast the universe is
    expanding (aka Hubble constant), we can determine
    the AGE OF THE UNIVERSE!

15
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16
  • Continuation of Expanding Universe
  • is expanding, therefore must have been smaller
    at one point
  • evident by galaxies red shift
  • most look red because they are moving away from
    us
  • if they were moving towards us, they would look
    bluer (blue shift)

17
Observers looking at an object that is moving
away from them see light that has a longer
wavelength than it had when it was emitted (a
redshift), while observers looking at an
approaching source see light that is shifted to
shorter wavelength (a blueshift).
18
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19
Cosmic background radiation
  • scientists found noise in our galaxy that was
    the cosmic microwave background radiation
    predicted by the Big Bang theory
  • The radiation can only be detected with a radio
    telescope which makes it show as a faint glow.
  • Thermal radiation thought to be left over by Big
    Bang
  • Happened 300,000 years after The Big Bang (so
    still about 13.7 billion years ago!)

20
What is a radio telescope?
  • Radio waves are a form of electromagnetic
    radiation, just like visible light!
  • How they work?
  • -waves bounce off a radio telescope, with this
    information computers can make images of the sky!

21
Can make images like this of our Universe!
22
New Evidence!
  • Theory of inflation
  • -first proposed in 1980s but recently found
    evidence for it!
  • -Found evidence that the universe was expanding
    exponentially seconds after the Big Bang

23
Life Cycle of Stars
  • Our sun is an average star in our solar system!
  • life cycle varies depending on the size
  • For most stars, 90 of life cycle is spent fusing
    hydrogen that turns into helium
  • all begin life inside a huge cloud of gas (mostly
    hydrogen) and dust called a nebula

24
When an average star ends its life cycle!
  • hydrogen fusion stops
  • Fusing of helium begins to create heavier
    elements (like oxygen, iron)
  • no more energy exploding outward
  • gravity pulls matter inwards
  • First makes a large red giant
  • outer layers often expand and drift away creating
    a planetary nebula
  • VERY high density, bright, and is called a white
    dwarf

25
Life cycle of Larger Stars
  • for larger stars
  • elements up to iron are fused together
  • eventually may turn into a supernova
  • quickly collapses because run out of energy and
    gravity is now the strongest force
  • core collapses and then rebounds outward with a
    shock wave that makes a bright explosion
    (supernova)
  • at this point, the heavier elements are finally
    created
  • if the leftover core is very, very dense, it may
    form a very small neutron star or a black hole
    with VERY powerful gravity

26
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27
Cosmology
  • How did the cosmos begin, and what will happen to
    it?
  • Study of the history and future of the universe
  • Universe everything that exists in space and
    time
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