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THE SUN

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Title: PowerPoint Presentation Author: Julie A. Rathbun Last modified by: Tyler_Nordgren Created Date: 8/14/2001 6:19:29 PM Document presentation format – PowerPoint PPT presentation

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Title: THE SUN


1
THE SUN
  • The star we see but seldom notice

2
Goals
  • Summarize the overall properties of the Sun.
  • What are the different parts of the Sun and how
    do we know this?
  • Where does the light we see come from?
  • Solar activity and magnetic fields.

3
The Sun, Our Star
  • The Sun is an average star.
  • From the Sun, we base our understanding of all
    stars in the Universe.
  • Like Jovian Planets its a giant ball of gas.
  • No solid surface.

4
Vital Statistics
  • Radius 100 x Earth (696,000 km)
  • Mass 300,000 x Earth (1.99 x 1030 kg)
  • Surface temp 5780 K
  • Core temp 15,000,000 K
  • Luminosity 4 x 1026 Watts
  • Solar Day
  • 24.9 Earth days (equator)
  • 29.8 Earth days (poles)

5
Structure
  • Surface
  • Photosphere
  • Atmosphere
  • Chromosphere
  • Transistion zone
  • Corona
  • Solar wind
  • Interior
  • Convection zone
  • Radiation zone
  • Core

6
The Solar Interior
  • How do we know whats inside the Sun?
  • Observe the outside.
  • Theorize what happens on the inside.
  • Complex computer programs model the theory.
  • Model predicts what will happen on the outside.
  • Compare model prediction with observations of the
    outside.
  • Scientific Method!

7
Helioseismology
  • Continuous monitoring of Sun.
  • Ground based observatories
  • One spacecraft (SOHO)
  • Surface of the Sun is ringing
  • Sound waves cross the the solar interior and
    reflect off of the surface (photosphere).

8
Interior Properties
  • Core 20 x density of iron
  • Surface 10,000 x less dense than air
  • Average density Jupiter
  • Core 15,000,000 K
  • Surface 5780 K

9
Do you see the light?
  • Everything in the solar system reflects light.
  • Everything also absorbs light and heats up
    producing blackbody radiation.
  • Q Where does this light come from?
  • A The Sun.
  • But where does the Suns light come from?

10
Our Journey through the Sun
  • Journey from the Suns core to the edge of its
    atmosphere.
  • See where its light originates.
  • See what the different regions of the Sun are
    like.
  • See how energy in the core makes it to the light
    we see on Earth.

11
In The Core
  • Density 20 x density of Iron
  • Temperature 15,000,000 K
  • Hydrogen atoms fuse together
  • Create Helium atoms.

12
Nuclear Fusion
  • 4H ? He
  • The mass of 4 H atoms
  • 4 x (1.674 x10-27 kg) 6.694 x 10-27 kg
  • The mass of He atom 6.646 x 10-27 kg
  • Where does the extra 4.8 x 10-29 kg go?
  • ENERGY! ? E mc2
  • E (4.8 x 10-29 kg ) x (3.0 x 108 m/s)2
  • E hc/l ? l 4.6 x 10-14 m (gamma rays)
  • So 4H ? He light!

13
The Radiation Zone
  • This region is transparent to light.
  • Why?
  • At the temperatures near the core all atoms are
    ionized.
  • Electrons float freely from nuclei
  • If light wave hits atom, no electron to absorb
    it.
  • So Light and atoms dont interact.
  • Energy is passed from core, through this region,
    and towards surface by radiation.

14
The Convection Zone
  • This region is totally opaque to light.
  • Why?
  • Closer to surface, the temperature is cooler.
  • Atoms are no longer ionized.
  • Electrons around nuclei can absorb light from
    below.
  • No light from core ever reaches the surface!
  • But where does the energy in the light go?
  • Energy instead makes it to the surface by
    convection.

15
Convection
  • A pot of boiling water
  • Hot material rises.
  • Cooler material sinks.
  • The energy from the pots hot bottom is
    physically carried by the convection cells in the
    water to the surface.
  • Same for the Sun.

16
Solar Cross-Section
  • Progressively smaller convection cells carry the
    energy towards surface.
  • See tops of these cells as granules.

17
The Photosphere
  • This is the origin of the 5800 K blackbody
    radiation we see.
  • Why?
  • At the photosphere, the density is so low that
    the gas is again transparent to light.
  • The hot convection cell tops radiate energy as a
    function of their temperature (5800 K).
  • l k/T k/(5800 K) ? l 480 nm (visible
    light)
  • This is the light we see.
  • Thats why we see this as the surface.

18
The Solar Atmosphere
  • Above the photosphere, transparent to light.
  • Unlike radiative zone, here atoms not totally
    ionized.
  • Therefore, there are electrons in atoms able to
    absorb light.
  • Absorption lines in solar spectrum are from these
    layers in the atmosphere.

19
Atmospheric Composition
  • Probably same as interior.
  • Same as seen on Jupiter.
  • Same as the rest of the Universe.

20
The Chromosphere
  • Very low density
  • But also very hot
  • Same as the gas tubes we saw in class and lab.
  • Energy from below excites the atoms and produces
    emission from this layer.
  • Predominant element Hydrogen.
  • Brightest hydrogen line Ha.
  • Chromosphere color

21
Spicules and Prominences
  • Emission from the atmosphere is very faint
    relative to photosphere.
  • Violent storms in the Chromosphere.
  • Giant curved prominances
  • Long thin spicules.

22
Prominences
23
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24
Ha Sun
Photo by Robert Gendler
25
Corona
  • Spicules and other magnetic activity carry energy
    up to the Transition Zone.
  • 10,000 km above photosphere.
  • Temperature climbs to 1,000,000 K
  • Remember photosphere is only 5800 K
  • The hot, low density, gas at this altitude emits
    the radiation we see as the Corona.

26
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27
The X-Ray Sun
  • Q At 1,000,000 K where does a blackbody spectrum
    have its peak?
  • A X-rays
  • Can monitor the Solar Coronasphere in the X-ray
    spectrum.
  • Monitor Coronal Holes

28
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29
Solar Wind
  • At and above the corona
  • Gas is very hot
  • Very energetic
  • Like steam above our boiling pot of water, the
    gas evaporates.
  • Wind passes out through Coronal Holes
  • Solar Wind carries away a million tons of Suns
    mass each second!
  • Only 0.1 of total Suns mass in last 4.6 billion
    years.

30
The Aurora
  • The solar wind passes out through the Solar
    System.
  • Consists of electrons, protons and other charged
    particles stripped from the Suns surface.
  • Interaction with planetary magnetic fields gives
    rise to the aurora.

31
The Active Sun
  • Solar luminosity is nearly constant.
  • Very slight fluctuations.
  • 11-year cycle of activity.

32
Solar Cycle
  • Increase in Coronal holes
  • Increase in solar wind activity
  • - Coronal Mass Ejections
  • Increase in Auroral displays on Earth
  • Increase in disruptions on and around Earth.

33
Sunspots
  • 11-year sunspot cycle.
  • Center Umbra 4500 K
  • Edge Penumbra 5500 K
  • Photosphere 5800 K

34
  • Can see that Sun doesnt rotate as a solid body?
  • Equator rotates faster.
  • This differential rotation leads to complications
    in the Solar magnetic field.

35
Magnetic fields and Sunspots
  • At kinks, disruption in convection cells.
  • Sunspots form.

36
Magnetic fields and Sunspots
  • Sunspots come in pairs.
  • Opposite orientation in North and South.
  • Every other cycle the magnetic fields switch.

37
Sunspot Numbers
38
Active Regions
  • Areas around sunspots give rise to the prominences
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