1 march 2005ast 2010: chapter 14 1 the sun: a garden -variety star
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1 March 2005 AST 2010: Chapter 14 1
The Sun:The Sun: A Garden -A Garden -
Variety StarVariety Star
1 March 2005 AST 2010: Chapter 14 2
The SunBiggest object in the solar system
diameter 1,392,000 km109 x Earth’s diameter10 x Jupiter’s diameter
Most Massive 333,000 x Earth’s mass1,000 x Jupiter’s massso heavy, everything else orbits around it! so heavy, it makes its own heat and light
Temperature of 15,000,000 K in its corenuclear power!
1 March 2005 AST 2010: Chapter 14 3
The Sun’s Profile
1 March 2005 AST 2010: Chapter 14 4
The Sun’s CompositionThe Sun contains the same elements as the Earth, but not in the same proportionsAbout 73% of the Sun’s mass is comes from hydrogen, and another 25% from helium
Other chemical elements make up the rest 2%
The fact that the Sun are mostly made up of H and He was first shown by Cecilia Payne-Gaposchkin
The 1st woman to get a PhD in astronomy in the U.S.
Elements Fraction
Hydrogen 92.1%
Helium 7.8%
Oxygen 0.061%
Carbon 0.030%
Nitrogen 0.0084%
Neon 0.0076%
Iron 0.0037%
Silicon 0.0031%
Magnesium 0.0024%
Sulfur 0.0015%
All others 0.0015%
1 March 2005 AST 2010: Chapter 14 5
The parts of the SunThe parts of the Sun
1 March 2005 AST 2010: Chapter 14 6
The Sun's InteriorFrom inside out:
CoreRadiative zone Convection zone Photosphere ChromosphereTransition region Corona
1 March 2005 AST 2010: Chapter 14 7
The Sun's CoreThe core
is the innermost 10% of the Sun's massgenerates energy from nuclear fusion has the highest temperature and density
temperature 10 million Kdensity = 160 x density of water = 20 x density of ironat this temperature, the core is a gasno molten interior
1 March 2005 AST 2010: Chapter 14 8
How does Heat from the Core Reach Us?
Three ways to transfer heat:Conduction: direct contact
A spoon in a hot cup of coffee gets warm
Convection: moving currents in a fluid
Hot air risesHot current in boiling water
Radiation: electromagnetic waves emitted by a heat source and absorbed by a cooler material
Electric stove
Heat from the Sun reaches us through the EM waves it emits
1 March 2005 AST 2010: Chapter 14 9
Radiative ZoneRadiation transfers heat from the interior of the Sun to its "cooler" outer layersThe core & radiation zone make up 85% of the SunThe temperature drops from 10 million K at the inner side of the radiative zone to 2 million K at its edgeThe energy generated in the core is carried by photons that bounce from particle to particle through the radiative zone
The photons are too energetic to be absorbed by atomsEach photon bounces so many times that it is estimated to take one million years to reach the outer edge of the region
1 March 2005 AST 2010: Chapter 14 10
Convection ZoneMatter at the base of the convection zone is “cool” enough (2 million K) for the atoms to absorb energy and hold on to it Convection occurs in this region The hotter material near the top of the radiation zone (the bottom of the convection zone) rises while the cooler material sinks — heated below like a pot of boiling waterIt takes a week for the hot material to carry its energy to the top of the convection zone
radiative zone
hot
cool
convection zoneconvection zone
1 March 2005 AST 2010: Chapter 14 11
PhotosphereThis is the Sun’s deepest layer that one can see from the outside Photosphere means “light sphere”It is the visible “surface” of the Sun
From this layer, photons can finally escape to spaceThe surface is not something one could land or float on
The photosphere is about 500 km thickThe gas is so dense that you could not see through itThe gas emits a continuous spectrum of light
It features sunspots
1 March 2005 AST 2010: Chapter 14 12
Temperature of Photosphere The photosphere temperature is about 5,800 KThe sunspots appear darker because they are cooler than their surroundings
The center of a typical sunspot has a temperature of 4,000 K
The spectrum and energy output of the radiation emitted from the photosphere obey Wien’s Law and Stefan-Boltzmann law
1 March 2005 AST 2010: Chapter 14 13
Features of PhotosphereSunspots
dark spots, 1500 K, cooler than surroundings glow by themselves
granulestops of convection cells700 to 1000 km diameterlast 10 minutescenters ~ 100 K hotter than edges
1 March 2005 AST 2010: Chapter 14 14
SunspotsDiscovered by Galileo GalileiSun's surface sprinkled with small dark regions - sunspotsSunspots are darker because they are cooler by 1000 to 1500 K than the rest of the photosphere Spots can last a few days or as long as a few months Galileo used the longer-lasting sunspots to map the rotation patterns of the SunSunspots number varies in a cycle with an average period of 11 years
Cycle starts with minimum and most of them are at around 35° from the solar equator At solar maximum (number peaked), about 5.5 years later, most of the sunspots are within just 5° of the solar equator
1 March 2005 AST 2010: Chapter 14 15
1 March 2005 AST 2010: Chapter 14 16
1 March 2005 AST 2010: Chapter 14 17
Sunspots and Magnetic FieldSunspots = regions of strong magnetic fieldsFound by observation of Zeeman effect
1 March 2005 AST 2010: Chapter 14 18
Sun RotatesGalileo
discovered sunspotssunspots moved sun rotates
Rotation – speed depends on latitude
equator once/25 days30º N once/26.5 days60º N once/30 daysJupiter also does this
1 March 2005 AST 2010: Chapter 14 19
1 March 2005 AST 2010: Chapter 14 20
ChromosphereVisible during solar eclipses as a thin pink layer at the edge of the dark MoonColorful layer – “color sphere”
Color due to hydrogen bright emission lineAlso shows yellow emission due to helium – discovered in 1868 – new element previously not seen on Earth
Helium was found on Earth in 1895
The chromosphere is only 2,000 to 3,000 km thickTemperature rises outward away from the photosphere – from 4,500 K to 10,000 K
1 March 2005 AST 2010: Chapter 14 21
Transition RegionIt’s a thin region (about 10 km thick) in the Sun’s atmosphere where temperature changes from 10,000 K to nearly 1,000,000 K
1 March 2005 AST 2010: Chapter 14 22
Solar WeatherThe Sun has complex and violent weather patternsChromosphere contains jet-like spikes of gas – called spiculesSpicules rise vertically through the chromosphereLast 10 minutesConsist of gas jets, at 30 km/s Rise to heights of 5000 to 20000 kmT ~ chromosphere
1 March 2005 AST 2010: Chapter 14 23
Corona (1)The outermost part of the Sun’s atmosphere is called the corona It is visible during total solar eclipses as a pearly-white glow around the dark Moon The corona has a very high temperature of ~1-2 million KIt is known to be very hot because it contains multiply ionized atoms
At very high temperatures, atoms like iron can have 9 to 13 electrons ejected (the atoms become ionized)9-times ionized iron is only produced at a temperature of 1.3 million K 13-times ionized iron means the temperature gets up to 2.3 million K!
Total solar eclipse in 1973Total solar eclipse in 1973
1 March 2005 AST 2010: Chapter 14 24
Corona (2)Most of the corona is trapped close to Sun by loops of magnetic field lines
In X-rays, those regions appear bright
Some magnetic field lines do not loop back to the Sun and will appear dark in X-rays
These are called coronal holes
More details visible at short wavelengths
A solar eclipse photographed in the extreme ultraviolet taken by the SOHO spacecraft
1 March 2005 AST 2010: Chapter 14 25
X-rays from the Corona
1 March 2005 AST 2010: Chapter 14 26
ProminencesBright clouds of gas forming above the sunspotsQuiet prominences
40,000 km above surfaceLast days to several weeks
Eruptive prominences700 km/sRareSurge prominences
Last up to a few hours Shoot gas up to 300,000 kmGas speed ~1300 km/s
1 March 2005 AST 2010: Chapter 14 27
Prominences follow magnetic-field
loops
1 March 2005 AST 2010: Chapter 14 28
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1 March 2005 AST 2010: Chapter 14 30
Solar FlaresSolar flares are eruptions more powerful than surge prominencesFlares last from a few minutes to a few hoursA lot of ionized material is ejected in a flareUnlike the material in prominences, the solar-flare material moves with enough energy to escape the Sun's gravityWhen such a burst of ions reaches the Earth, it interferes with radio communicationSometimes a solar flare will cause voltage pulses or surges in power and telephone lines
Brownouts or blackouts may result
Humans traveling outside the protection of the Earth's magnetic field will need to have shielding from the powerful ions in a flare
1 March 2005 AST 2010: Chapter 14 31
1 March 2005 AST 2010: Chapter 14 32
Solar WindFast-moving charged particles (mostly protons and electrons) can escape the Sun's gravitational attractionThe stream of particles is called the solar windThey move outward at a speed of about 400 km/s
They can reach the farthest reaches of the solar system
Solar-wind particles passing close to a planet with a magnetic field are deflected around the planet
Some are deflected to the planet's magnetic polesAs the particles hit the planet's atmosphere, they cause the molecules in the atmosphere to produce beautiful curtains of light called the auroras
Aurora borealis in the northern hemisphere Aurora australis in the southern hemisphere
1 March 2005 AST 2010: Chapter 14 33
Is the Sun a Variable Star?What is more certain than that the Sun will rise tomorrow?We’ve already seen that sunspots follow an 11-year cycleOn longer time scales, the Sun undergoes changes in overall activityChanges are only about 0.1%!
Yet this is enough to affect our climate
In the mid 1600’s the Sun’s output was particularly low the “Little Ice Age”Other stars are seen to vary by 0.3%, up to 1%