Lecture 4: The Superficial Sun- Atmosphere and Composition

"Long is the way, And hard, that out of hell leads up to light."
Milton, Paradise Lost

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Date: February 2, 1995
Reading Assignment: pp. 365-379

Description : solar atmosphere, composition, activity and sun spots

Objectives

be able to describe the mass, density, size, luminosity and surface temperature of the Sun

be able to distinguish between the solar atmosphere and the solar interior

be able to distinguish between the corona, the chromosphere and the photosphere in position, size and temperature

be able to understand how temperature and surface area are related to luminosity

be able to understand the differences between granulation, super granulation, and convection cells

be able to understand why limb darkening occurs

be able to understand what sunspots are and why they appear black

be able to understand the connections between the solar magnetic field and sunspots, including the 11 year solar cycle

be able to distinguish between solar flares and prominences

Lecture Outline

Slide # 1: The Superficial Sun

Solar Atmosphere and Composition

Slide # 2: Thermal Radiation (GRAPHICS)

the Planck Curve

Slide # 3: Doppler

Blue Shift

higher frequencies, shorter wavelength

the observer moves toward the source

the source moves toward the observer

Red Shift

lower frequencies, longer wavelengths

the observer moves away from the source

the source moves away from the observer

Slide # 4: Continuous and Line Spectra (GRAPHICS)

Continuous Spectra have no spectral lines

Slide # 5: Spectral Lines (GRAPHICS)

Absorption lines are dark

Emission lines are bright

Slide # 6: The Bohr Model (GRAPHICS)

the hydrogen atom

Slide # 7: Electrons can only have certain discrete energy levels (GRAPHICS)

discrete energy states

Slide # 8: Two Types of Excitation

Collisionally

atoms collide with other atoms

Radiatively

photons hit the atom

only photons of the correct energy excite atoms

Slide # 9: Transitions to Ground State

in 10-8 seconds, electron returns to the ground state

when electrons move to lower energy states, they radiate

the difference in the energy of the states is equal to the photon energy

Slide # 10: Emission and Absorption (GRAPHICS)

both emission and absorption can occur from the same gas

Slide # 11: Line Intensity (GRAPHICS)

temperature determines line intensity

Slide # 12: The Sun

describe the physical characteristics

distinguish between interior and atmosphere

identify characteristics of the atmosphere

describe limb darkening

describe convection and radiative transfer

discuss sunspots and the sunspot cycle

distinguish between prominences, flares, and the solar wind

Slide # 13: Solar Interior (GRAPHICS)

cross sectional view

Slide # 14: The Sun

Interior

core

interior (radiative zone)

convection zone

Atmosphere

photosphere

chromosphere

corona

Slide # 15: The Sun (GRAPHICS)

mass = 2 x 1033 grams

(300,000 Earth masses)

Slide # 16: The Sun (GRAPHICS)

radius = 700,000 km

(100 times EarthÕs radius)

Slide # 17: The Sun (GRAPHICS)

density = 1.4 grams/cm3

(1/4 EarthÕs density)

Slide # 18: Surface Temperature (GRAPHICS)

5,800 K

Slide # 19: Luminosity (GRAPHICS)

total energy produced by the Sun

4 x 1026 watts

4 trillion trillion 100 watt light bulbs

Slide # 20: The SunÕs Surface

the Sun does not have a SOLID surface

it does have a photosphere

you cannot see past the photosphere

Slide # 21: Energy Transport

energy is created in the core

travels to the photosphere in two ways

convection

radiation

Slide # 22: Convection

energy is transferred through moving matter

hotter material rises

cooler material sinks

Slide # 23: Convection (GRAPHICS)

material rises

Slide # 24: Convection (GRAPHICS)

Material sinks

Slide # 25: Convection Examples

thunderstorms

boiling water

turbulence in aircraft

Slide # 26: Convection Inside the Sun

Convection transports energy from the interior to the photosphere

We can observe the tops of the convection cells

granulation

super granulation

Slide # 27: Radiation

energy is transported by photons

photons move, not the gas

photons may be deflected, but they carry the energy

Slide # 28: Radiation

photons carry the energy

Slide # 29: Solar Interior

cross sectional view

Slide # 30: The Edge of the Sun

the edge of the Sun appears darker than the center

this is called Limb Darkening

Slide # 31: Limb Darkening (GRAPHICS)

the limb of the Sun appears darker than the center of the disk

Slide # 32: Limb Darkening

Photons near the limb originate higher in the Solar photosphere

Temperatures in the upper photosphere are lower

Lower temperatures produce less energy

StephanÕs Law

The limb emits less energy than the center of the Solar disk

Slide # 33: Solar Granulation Slide # 34: Coronal Heating (GRAPHICS)

the temperature of the Corona is much higher than the chromosphere

Slide # 35: Coronal Heating

energy is probably transfer to the Cornoa through magnetic fields

Slide # 36: The Solar Corona (GRAPHICS)

hot outer region of solar atmosphere

Slide # 37: The Solar Chromosphere (GRAPHICS)

cooler region outside photosphere

Slide # 38: Solar Limb (GRAPHICS)

the diamond ring effect

Slide # 39: Constellation Corner (GRAPHICS)

The Constellation de Jour

Slide # 40: Cassiopeia (GRAPHICS)

Fairfax - Feb 1 - 10pm - N - 6.0

Slide # 41: Cassiopeia (GRAPHICS)

Fairfax - Feb 1 - 10pm - N - 5.0

Slide # 42: Cassiopeia (GRAPHICS)

Fairfax - Feb 1 - 10pm - N - 4.0

Slide # 43: Cassiopeia (GRAPHICS)

Fairfax - Feb 1 - 10pm - N - 4.0

Slide # 44: H-alpha Image of the Sun (GRAPHICS)

January 29, 1995

Slide # 45: Sunspots

sunspots are dark areas seen on the SunÕs disk

sunspots are always found in pairs or groups

Slide # 46: Sunspot Image (GRAPHICS)

closeup of a sunspot group

Slide # 47: Why are Sunspots dark?

Sunspots have temperatures of 4000K

The disk has a temperature of 6000K

Sunspots produce (2/3)4 as much energy as the surrounding disk

(2/3)4 = 16/81 or about 1/5 as much energy flux

They appear dark because they donÕt produce as much light

Slide # 48: Solar Magnetic Field

sunspots have very high magnetic fields

1000 times greater than the surrounding photosphere

sunspot pairs have opposite polarity

Slide # 49: Sunspot Pairs (GRAPHICS)

magnetic fields connect sunspot pairs

Slide # 50: Magnetic Fields

the magnetic polarity switches between the Northern and Southern Solar Hemisph

Slide # 51: Magnetograph of the Sun (GRAPHICS)

January 28, 1995

Slide # 52: The Sunspot Cycle (GRAPHICS)

the number and average latitude of sunpots varies of an 11-year cycle

Slide # 53: Sunspot Cycle

solar minimum - only a few spots seen between 30 and 45 degrees from the Solar

solar maximum - many spots seen between 10 and 15 degrees from the Solar Equat

Slide # 54: The Solar Cycle

22 years long or TWO sunspot cycles

the magnetic field of the Sun completely reverses

Slide # 55: The Maunder Minimum

virtually no sunspots were seen between 1645 and 1715

corresponds to the ÒLittle Ice AgeÓ in Europe

Slide # 56: Prominences (GRAPHICS)

Skylab 1973- ultraviolet image

Slide # 57: Solar Activity

Prominences

10 times the size of Earth

active prominences form in hours

quiescent prominences form in days

Solar Flares

very energetic

100 million K temperature

form in minutes

Slide # 58: Magnetograph of the Sun (GRAPHICS)

January 28, 1995

Slide # 59: X-ray Image of the Sun (GRAPHICS)

January 28, 1995

Slide # 60: Solar Activity

the amount of flares and prominences is tied to the Solar Cycle

lots of sunspots usually means lots of active regions