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GE 150 Astronomy. Week #10 March 26 , 2013. What can we learn by analyzing starlight?. A star’s temperature A star’s chemical composition. - peak wavelength of the spectral curve. - dips in the spectral curve or the lines in the absorption spectrum. A star’s motion. The Doppler Effect.

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ge 150 astronomy
GE 150 Astronomy

Week #10

March 26, 2013

what can we learn by analyzing starlight
What can we learn by analyzing starlight?
  • A star’s temperature
  • A star’s chemical composition

- peak wavelength of the spectral curve

- dips in the spectral curve or the lines in the absorption spectrum

  • A star’s motion
the doppler effect
The Doppler Effect
  • Definition:“The change in wavelength (of either light or sound) due to the relative motion between the source and the observer along the line of sight.”
slide4
Astronomers use the Doppler Effect to learn about the relative motions of stars, and other astronomical objects
real life examples of doppler effect
Real Life Examples of Doppler Effect
  • Doppler Radar (for weather)
  • Airplane radar system
    • Ok, anything with radar
  • Radar gun, used by Law Enforcement Officers…
the doppler effect1
The Doppler Effect
  • When something which is giving off light moves towardsorawayfrom you, the wavelength of the emitted light is changed or shifted

V=0

the doppler effect2
The Doppler Effect
  • When the source of light is moving away from the observer the wavelength of the emitted light will appear to increase. We call this a “redshift”.

Unshifted

the doppler effect3
The Doppler Effect
  • When the source of light is moving towards the observer the wavelength of the emitted light will appear to decrease. We call this a “blueshift”.

Unshifted

slide9
“Along the line of sight” means the Doppler Effect happens only if the object which is emitting light is moving towards you or away from you.

An object moving “side to side” or perpendicular, relative to your line of sight, will not experience a Doppler Effect.

Unshifted

doppler shifts
Doppler Shifts
  • Redshift (to longer wavelengths): The source is moving awayfrom the observer
  • Blueshift (to shorter wavelengths): The source is moving towards the observer

Dl = difference of shifted and unshifted

l0= wavelength when source is not moving

v = velocity of source

c = speed of light

doppler effect in light
Doppler Effect in Light

H alpha λ0=656 nm

Δλ

= 22 nm

c

stars1
Stars
  • Start by studying the closest star: the Sun
  • What tools do have so far:
    • Blackbody Spectrum/Wien’s Law
      • How energy is distributed with wavelength
      • Surface Temperature
    • Emission/Absorption lines
      • Composition
  • Use these and some new concepts to determine structure of the Sun
the sun the largest object in solar system
The Sun: the largest object in Solar System
  • The Sun contains more than 99.85% of the total mass of the solar system
  • Allthe planets in the solar system together would not fill up the volume of the Sun
  • 110 Earths or 10 Jupiters fit across the diameter of the Sun
the sun s interior has three layers

Core

Radiative zone

Convective zone

The Sun’s interior has three layers:

Energy generated in the core of the Sun propagates outward

through these different layers, and finally, through the

atmosphere of the Sun. This process takes 100 thousand years or more.

energy transport in the sun
Energy Transport in the Sun
  • The Core
    • Source of all the Sun’s Energy
      • Only 10 % of the Sun’s mass
      • Only part of the Sun available for “fuel”
energy transport in the sun1
Energy Transport in the Sun
  • RadiativeZone
    • Energy from the core is transported outward by of photons (i.e. radiation)
      • Cooler than core but gas is still very hot and very dense
      • Photons (x & gamma rays) are absorbed/re-emitted every 1 cm
energy transport in the sun2
Energy Transport in the Sun
  • Convection Zone
    • hot gas rises, dumps its energy onto the surface and then sinks
    • similar to a pot of boiling water
the sun s atmosphere also has three layers
The Sun’s atmosphere also has three layers…

Photosphere - the layer we see: 5800 K

Sun is opaque below this layer

Chromosphere - the red layer observed using a hydrogen filter: 10,000 K

Corona- the incredibly thin outer atmosphere: 1,000,000 K

Last two layers only visible

during eclipses

Corona

Chromosphere

Photosphere

the photosphere is the visible layer of the sun

Hotter gas here is rising (blueshifted)

The photosphere is the visible layer of the Sun

Cooler gas here is falling (Redshifted)

Granulation caused by convection

sunspots
Sunspots
  • Sunspots are highly localized cool regions in the photosphere of the Sun
    • First observed by Galileo in 1609
    • Can be many times larger than the Earth
    • Appear darker, in contrast, because they cooler than surroundings

4500 K

slide24
Galileo used the movement of sunspotsacross the Sun’s surface reveals that the it rotates once in about …

4 weeks

the annual change in numbers of sunspots reveals that the sun experiences an 11 year sun spot cycle
The annual change in numbers of sunspots reveals that the Sun experiences an 11-year Sun Spot cycle

Next Peak 2013-2014

slide26

Sunspots: Max Vs Min

July 19, 2000

March 18, 2009

slide27

An Ultraviolet look…

July 19, 2000

March 18, 2009

slide32
prominences

solar flares

Solar magnetic fields also create other atmospheric phenomena

above the photosphere the chromosphere is characterized by its red color from h a emission
Above the photosphere, the chromosphere is characterized by its redcolor – from Haemission.

1500 km

Chromosphere satisfies the conditions for Kirchkoff’s 2nd Law

slide34
The corona, the outermost part of the Sun’s atmosphere, is characterized by its high temperature and low density

It expands into space as a stream of charged particles known as the solar wind

solar magnetic fields also create other atmospheric phenomena1
Solar magnetic fields also create other atmospheric phenomena

prominences

solar flares

coronal mass ejections (CMEs)

slide37

The most powerful solar flare in 14 years, .. erupted from sunspot 486 in late October of 2003.

The explosion hurled a coronal mass ejection (CME) almost directly toward Earth, which triggered bright auroras when it arrived on Earth.

slide39
The Earth’s magnetic field produces a magnetosphere that deflects and traps particles from the solar wind protecting Earth
relevance of earth s protective magnetosphere
Relevance of Earth’s protective magnetosphere
  • Protects against Solar Flares/CMEs- violent explosions on the Sun releasing large burst of charged particles into the solar system
  • Protects against Solar Wind - dangerous stream of charged particles constantly coming from the Sun
  • Northern Lights (Aurora Borealis)
slide41

Northern Lights (Aurora Borealis)

Charged particles from the Sun interact with the magnetic field around Earth.

The particles collide with the nitrogen and oxygen atoms in the extreme upper atmosphere (ionosphere) and excite those atoms to emit light

the aurora
The Aurora
  • Caused when CME material reaches the Earth, it interacts with the Earth’s magnetic field, and collides with ionospheric particles