Starry Monday at Otterbein

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Starry Monday at Otterbein
Welcome to

• Astronomy Lecture Series
• -every first Monday of the month-
• April 4, 2005
• Dr. Uwe Trittmann

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Todays Topics

• Spectra Fingerprints of the Elements
• The Night Sky in March

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Feedback!

• Please write down suggestions/your interests on
  the note pads provided
• If you would like to hear from us, please leave
  your email / address
• To learn more about astronomy and physics at
  Otterbein, please visit
• http//www.otterbein.edu/dept/PHYS/weitkamp.asp
  (Obs.)
• http//www.otterbein.edu/dept/PHYS/ (Physics
  Dept.)

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Light and Spectra

• Color of light determined by its wavelength
• White (visible) light is a mixture of all colors
• Can separate individual colors with a prism

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Light is an electromagnetic Wave

• Medium electric and magnetic field
• Speed 3 ?105 km/sec

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Electromagnetic Spectrum
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Visible Light

• 400440 nm Violet
• 440480 nm Blue
• 480530 nm Green
• 530590 nm Yellow
• 590630 nm Orange
• 630700 nm Red

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Three Things Light Tells Us

• Temperature
• from black body spectrum
• Chemical composition
• from spectral lines
• Radial velocity
• from Doppler shift

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Black Body Spectrum (gives away the temperature)
Peak frequency

• All objects - even you - emit radiation of all
  frequencies, but with different intensities

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Cool, invisible galactic gas (60 K, mostly low
radio frequency)
Dim, young star (600K, mostly infrared)
The Suns surface (6000K, mostly visible)
Hot stars in Omega Centauri (60,000K, mostly
ultraviolet)
The hotter the object, the higher the peak
frequency!
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Wiens Law

• The peak of the intensity curve will move with
  temperature, this is Wiens law
• Temperature / frequency constant
• So the higher the temperature T, the smaller
  the frequency f, i.e. the higher the energy of
  the electromagnetic wave

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Measuring Temperatures

• Find maximal intensity
• ? Temperature (Wiens law)

Identify spectral lines of ionized elements ?
Temperature
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Spectral Lines Fingerprints of the Elements

• Can use this to identify elements on distant
  objects!
• Different elements yield different emission
  spectra

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Origin of Spectral Lines

• Atoms electrons orbiting nuclei
• Chemistry deals only with electron orbits
  (electron exchange glues atoms together to from
  molecules)
• Nuclear power comes from the nucleus
• Nuclei are very small
• If electrons would orbit the statehouse on I-270,
  the nucleus would be a soccer ball in Gov. Bob
  Tafts office
• Nuclei made out of protons (el. positive) and
  neutrons (neutral)

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• The energy of the electron depends on orbit
• When an electron jumps from one orbital to
  another, it emits (emission line) or absorbs
  (absorption line) a photon of a certain energy
• The frequency of emitted or absorbed photon is
  related to its energy
• E h f
• (h is called Plancks constant, f is
  frequency)

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Origin of Spectral Lines Emission

• Heated Gas emits light at specific frequencies
• ? the positive fingerprints of the elements

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Origin of Spectral Lines Absorption

• Cool gas absorbs light at specific frequencies
• ? the negative fingerprints of the elements

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Spectral Lines

• Light of a low density hot gas consists of a
  series of discrete bright emission lines the
  positive fingerprints of its chemical elements!
  
• A cool, thin gas absorbs certain wavelengths from
  a continuous spectrum
  ? dark absorption (
  Fraunhofer) lines in continuous spectrum
  negative fingerprints of its chemical elements,
  precisely at the same wavelengths as emission
  lines.

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Doppler Shift
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Application Separate close Binary Stars

• Too distant to resolve the individual stars
• Can be viewed indirectly by observing the
  back-and-forth Doppler shifts of their spectral
  lines

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ApplicationClassification of the Stars

• Class Temperature Color Examples
• O 30,000 K blue
• B 20,000 K bluish Rigel
• A 10,000 K white Vega, Sirius
• F 8,000 K white Canopus
• G 6,000 K yellow Sun, ? Centauri
• K 4,000 K orange Arcturus
• M 3,000 K red Betelgeuse

Mnemotechnique Oh, Be A Fine Girl/Guy, Kiss Me
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The Hertzprung-Russell Diagram

• A plot of absolute luminosity (vertical scale)
  against spectral type or temperature (horizontal
  scale)
• Most stars (90) lie in a band known as the Main
  Sequence

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Hertzsprung-Russell diagrams

• of the closest stars of the brightest stars

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Stellar Lifetimes

• From the luminosity, we can determine the rate of
  energy release, and thus rate of fuel consumption
• Given the mass (amount of fuel to burn) we can
  obtain the lifetime
• Large hot blue stars 20 million years
• The Sun 10 billion years
• Small cool red dwarfs trillions of years
• ?The hotter, the shorter the life!

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The Night Sky in March

• The sun is getting higher -gt shorter nights!
• Spring constellations (Cancer,Leo,Coma,Virgo,)
  contain few bright stars but many galaxies
• Jupiter is in opposition this month (i.e. at its
  brightest)

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Moon Phases

• Today (Waning crescent, 20)
• 4 / 8 (New Moon)
• 4 / 16 (First Quarter Moon)
• 4 / 24 (Full Moon)
• 5 / 1 (Last Quarter Moon)

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Today at Noon

• Sun at meridian, i.e. exactly south

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10 PM

• Typical observing hour, early March
• no Moon
• Jupiter
• Saturn at meridian

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South-East

• Perseus and
• Auriga
• with Plejades and the Double Cluster

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Zenith

• Big Dipper points to the north pole

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South-West

• The Winter Constellations
• Orion
• Taurus
• Canis Major
• Gemini
• Canis Minor

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South

• Spring Constellations
• - Cancer
• - Leo
• - Hydra
• Deep Sky Objects
• - Beehive Cluster (M44)

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Mark your Calendars!

• Next Starry Monday at Otterbein May 2, 2005, 7
  pm
• (this is a Monday
  )
• Web pages
• http//www.otterbein.edu/dept/PHYS/weitkamp.asp
  (Obs.)
• http//www.otterbein.edu/dept/PHYS/ (Physics
  Dept.)

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Mark your Calendars II

• Physics Coffee is every Wednesday, 330 pm
• Open to the public, everyone welcome!
• Location across the hall, Science 256
• Free coffee, cookies, etc.
• Details about Otterbeins Rocket Contest there!