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Today’s APOD Homework and Quiz 9 Today Reading for next week on Oncourse The Sun Today A100 The Sun

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A100 The Sun. Homework and Quiz 9 Today Reading for next week on Oncourse. Today’s APOD. The Sun Today. Reading for next week available from the Resource Tool on Oncourse. Quiz 9 – Question 1: The diameter of the Sun is about how large compared to the diameter of the Earth?. Twice as big - PowerPoint PPT Presentation


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Today’s APOD

Homework and Quiz 9 TodayReading for next week on


The Sun Today

A100 The Sun

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Reading for next week available from the Resource Tool on Oncourse

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Quiz 9 – Question 1: The diameter of the Sun is about how large compared to the diameter of the Earth?

A. Twice as bigB. One half as bigC. 10 times as bigD. 100 times as bigE. 10,000 times as big

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Question 2: The Sun is supported against the crushing force of its own gravity by

A. Magnetic forcesB. Its rapid rotationC. The force exerted by escaping

neutrinosD. Gas pressureE. A solid, crystalline ball of metallic

hydrogen that fills the interior of the Sun

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What we covered on Wednesday:

Internal structure of the SunComposition of the SunSource of the Sun’s energyThe Sun’s lifetimeBalancing pressure, gravity, and

temperatureHelioseismologyWhat neutrinos tell us about the Sun

Today: The Sun’s Atmosphere

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Recall the structure of the Sun…

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The Sun’s Atmosphere: Photosphere, Chromosphere, Corona, Solar Wind

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Active regions

TheSun Corona


three layers of the Sun’s atmospherephotospherechromospherecorona

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Active regions


Limb darkening: …when we look near the Sun’s limb we do not see as deeply into the photosphere

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The photosphere is opaque to visible light

The density is only 1% the density of air

Temperature decreases from inside the Sun to a minimum of 4400K just above the photosphere

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convection cells ~ 1000 km (600 mi)

The difference in Tfrom center to edge is about 300 K

> hot gas from lower levels rises upward, cools off, and falls back into the Sun

Cells form and disappear in few minutes.

The Solar Photosphere – the layer we see


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The convection moves at 1400 km/h =900 mi/hSupergranules last about a day

Supergranules35,000 km in diameter

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Question 3: The Sun produces its energy from

A. Fusion of neutrinos into heliumB. Fusion of positrons into heliumC. Disintegration (fission) of helium

into hydrogenD. Fusion of hydrogen into heliumE. Electric currents generated in the


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Solar Atmosphere Absorption lines

from the photosphere and chromosphere

67 different elements in various stages of excitation and ionization

The spectrum gives us a picture of the physical conditions in the solar atmosphere

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Blotchy sunspots

appear on the Sun’s


Note also the “granulation” resulting fromconvection under the surface

Sunspot grouping

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Sunspots are low-temperature regions inthe Sun’s photosphere

Sometimes they are isolated but frequently in sunspost groups

~ diameter of Earth (lasting between hours or months)

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T (umbra) = 4300 KT (penumbra) = 5000 KT (photosphere = 5800 K

The brightness depends on the 4th power of the temperature (energy flux T4 )


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The number of sunspots varies in an 11 year cycle

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Question 4: Why are sunspots darker than their surroundings?

A. They are cool relative to the gas around them

B. They contain 10 times as much iron as surrounding regions

C. Nuclear reactions occur in them more slowly than in the surrounding gas

D. Clouds in the corona block our view of the hot photosphere

E. The gas within them is too hot to emit any light

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Magnetic Carpet




Above the photosphere, the

temperature increases again from 4400 K to

25,000 K at the top of the


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The chromosphere is characterized by spikes of rising gas

Above the photosphere, the gas density is much lower (10-4 less than the photosphere) but gas is much warmer (25,000 K)

Red color from the emission line of hot hydrogen

(Using Hydrogen filter)

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• Spicules last about 15 minutes• they rise at speeds of 20km/s• 300,000 spicules cover the Sun at any one time

Spicules: jets of rising gasSpicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules

dense jets of gas that shoot up from the


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Solar Wind

Coronal MassEjection


AuroraCoronal Holes

The corona, the outermost layer of the solar atmosphere, is made of very high-temperature gases at extremely low density

The solar corona blends into the solar wind at great distances from the Sun

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The corona extends for millionsof kilometers out from the Sun

a million times fainter

than the photosphere...

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In the narrow region between the chromosphere and the corona, the temperature rises abruptly to more than a million degrees!


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Activity in the corona

includes coronal mass ejections and coronal holes

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The Sun also produces huge

flares that burst into space A solar flare is a brief

eruption of hot, ionized gases from a sunspot group

A coronal mass ejection is a much larger eruption that involves immense amounts of gas from the corona

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The Solar Wind

The Sun is “evaporating” constantly (ONLY 0.1% of its mass since its formation)

Interact with objects in the solar system Earth: cause aurorae Comets: produces tails Interacts with edge of solar system: heliopause

Radiation reach Earth in 8 min, particles take a few days (v= 500 km/s)

Coronal particles (mostly electrons and protons)

are thrown with such velocity that they cannot

be held by the Sun’s gravity

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Active regions


Magnetic Carpet

Solar Wind

Coronal MassEjection


AuroraCoronal Holes




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The X-raySun



What causes all this violent activity on the Sun?????

Rotation and Magnetic Fields!



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Sunspots show

the Sun is



The Sun does not rotate rigidly: the equatorial regions rotate faster (25 days) than the poles (36 days) --- Differential Rotation

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The Sunrotates atdifferentrates at

different solar


Pequator=25 days

Ppole=36 days

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The Sun’s differential rotation winds up the Sun’s magnetic field, storing energyWhen the magnetic field suddenly unwinds, that energy is released

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The Solar MagneticField

The differential rotation “wraps up” the magneticfield of the Sun

Sunspots and othersolar activity are causedby the twisted magnetic field of the Sun

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Solar Activity Varies in an Eleven Year Cycle

The Sun’s magnetic field takes 11 years to twist up and then reestablish itself

The number of sunspots, as well as the number of violent events depends on the state of the magnetic field

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Variations in Sunspot Activity



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Question 5: How many years elapse between times of maximum solar activity?

A. 3B. 5C. 11D. 33E. 105

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Space Weather:

What is it?Space Weather refers to conditions in space that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health.


Sun: •Energy released in the form of photons, particles, and magnetic fields

•Sources of major disturbances:•Coronal Holes•Solar Flares•Coronal Mass Ejections•Solar Particle Events

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Hurricanes and Tornados

Weather Space Weather

Solar Corornal Mass Ejection

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Space Weather

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Geomagnetic Storm Effects Telegraph

Operations - September 3, 1859Boston (to Portland operator).--"Please cut off your battery entirely from the line for fifteen minutes."

Portland.--"Will do so. It is now disconnected."

Boston.--"Mine is also disconnected and we are working with the auroral current. How do you receive my writing?"

Portland.--"Better than with our batteries on. Current comes and goes gradually."

Boston.--"My current is very strong at times, and we can work better without batteries, as the aurora seems to neutralize and augment our batteries alternately, making the current too strong at times for our relay magnets. Suppose we work without batteries while we are affected by this trouble?"

Portland.--"Very well. Shall I go ahead with business?"

Boston.--"Yes. Go ahead."(Annual of Scientific Discovery, ed. by D.A. Wells, Boston, Gould and Lincoln, p414, 1860; Singer, H.J., Magnetospheric Pulsations, Model and Observations of Standing Alfven Wave Resonances, Thesis, UCLA, 1980.)

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1958 Geomagnetic StormOn February 9, 1958 an explosive brightening was observed on the solar disk at the Sacramento Peak Observatory

A notice was radioed to the IGY Data Center on Solar Activity at the Univ. Colorado’s High Altitude Observatory in Boulder

28 hours later one of the greatest magnetic storms on record began

It was the 13th most disturbed day from 1932 to the present


Toronto area plunged into temporary darknessWestern Union experienced serious interruptions on its nine North Atlantic telegraph cablesOverseas airlines communications problems

Brooks, J., The Subtle Storm, New Yorker Magazine, 39-77, Feb. 7, 1959.

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NOAANational Weather Service



Space WeatherNOAA Space Environment Center


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Unveiling of U-Haul Truck Supergraphic Representing Colorado at Space Weather Week 2001

Graphic on the side of several thousand U-Haul Trucks

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Solar “butterfly” diagram

At the beginning of the solar cycle, sunspots appear at high latitude on the Sun

As the cycle progresses, sunspots appear closer and closer to the solar equator

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