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

 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? A.Twice as big B.One half as big C.10 times as big D.100 times as big E.10,000 times as big

Question 2: The Sun is supported against the crushing force of its own gravity by A.Magnetic forces B.Its rapid rotation C.The force exerted by escaping neutrinos D.Gas pressure E.A solid, crystalline ball of metallic hydrogen that fills the interior of the Sun

What we covered on Wednesday:  Internal structure of the Sun  Composition of the Sun  Source of the Sun’s energy  The Sun’s lifetime  Balancing pressure, gravity, and temperature  Helioseismology  What neutrinos tell us about the Sun Today: The Sun’s Atmosphere

Recall the structure of the Sun…

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

Photosphere Umbra Penumbra Sunspots Active regions The Sun Corona Chromosphere  three layers of the Sun’s atmosphere  photosphere  chromosphere  corona

Photosphere Limb Convection Supergranules Granulation Limb darkening Umbra Penumbra Sunspots Active regions Prominence Limb darkening: …when we look near the Sun’s limb we do not see as deeply into the photosphere

Photosphere  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

convection cells ~ 1000 km (600 mi) The difference in T from 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 GRANULATION

The convection moves at 1400 km/h =900 mi/h Supergranules last about a day Supergranules 35,000 km in diameter

Question 3: The Sun produces its energy from A.Fusion of neutrinos into helium B.Fusion of positrons into helium C.Disintegration (fission) of helium into hydrogen D.Fusion of hydrogen into helium E.Electric currents generated in the core

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

Umbra Penumbra Blotchy sunspots appear on the Sun’s “surface” Note also the “granulation” resulting from convection under the surface Sunspot grouping

Sunspots are low-temperature regions in the Sun’s photosphere Sometimes they are isolated but frequently in sunspost groups ~ diameter of Earth (lasting between hours or months)

T (umbra) = 4300 K T (penumbra) = 5000 K T (photosphere = 5800 K The brightness depends on the 4 th power of the temperature (energy flux  T 4 ) Photosphere

The number of sunspots varies in an 11 year cycle

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

Magnetic Carpet Chromosphere Spicules Prominence Above the photosphere, the temperature increases again from 4400 K to 25,000 K at the top of the chromosphere

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)

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 gas Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules dense jets of gas that shoot up from the chromosphere

Solar Wind Coronal Mass Ejection Corona Aurora Coronal 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

CORONA The corona extends for millions of kilometers out from the Sun a million times fainter than the photosphere...

In the narrow region between the chromosphere and the corona, the temperature rises abruptly to more than a million degrees! (BUT NOT MUCH HEAT!)

Activity in the corona includes coronal mass ejections and coronal holes

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

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

Photosphere Limb Convection Supergranules Granulation Limb darkening Umbra Penumbra Sunspots Active regions The Sun Magnetic Carpet Solar Wind Coronal Mass Ejection Corona Aurora Coronal Holes Chromosphere Spicules Prominence

The X-ray Sun coronal hole What causes all this violent activity on the Sun????? Rotation and Magnetic Fields! mass ejectio n

Sunspots show the Sun is rotating (Galileo!) The Sun does not rotate rigidly: the equatorial regions rotate faster (25 days) than the poles (36 days) --- Differential Rotation

The Sun rotates at different rates at different solar latitudes P equator =25 days P pole =36 days

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

The Solar Magnetic Field The differential rotation “wraps up” the magnetic field of the Sun Sunspots and other solar activity are caused by the twisted magnetic field of the Sun

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

Variations in Sunspot Activity Maunder Minimum

Question 5: How many years elapse between times of maximum solar activity? A.3 B.5 C.11 D.33 E.105

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. Earth 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

SPACE WEATHER

Hurricanes and Tornados Weather Space Weather Solar Corornal Mass Ejection

Space Weather

Geomagnetic Storm Effects Telegraph Operations - September 3, 1859 Boston (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.)

1958 Geomagnetic Storm On 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 13 th most disturbed day from 1932 to the present Effects: Toronto area plunged into temporary darkness Western Union experienced serious interruptions on its nine North Atlantic telegraph cables Overseas airlines communications problems Brooks, J., The Subtle Storm, New Yorker Magazine, 39-77, Feb. 7, 1959.

NOAA National Weather Service Weather Accuweather Space Weather NOAA Space Environment Center MONITORING SPACE WEATHER

Unveiling of U-Haul Truck Supergraphic Representing Colorado at Space Weather Week 2001 Graphic on the side of several thousand U-Haul Trucks

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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