The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone,...

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The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields, the sunspot cycle Solar activity and how it influences the Earth

Transcript of The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone,...

Page 1: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

The Sun – A Typical Star

• The layers of the sun; core, radiative

zone, convective zone, photosphere, chromosphere, and corona

• Sunspots and magnetic fields, the sunspot cycle

• Solar activity and how it influences the Earth

Page 2: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Gravity vs. pressure

Page 3: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

A Star: A Balance between Gravity and

Pressure• Self-regulating…• Higher fusion rate would expand

star, lowering core’s self-gravity and thence density, pressure, temperature and thus lowering fusion rate. And vice versa

Page 4: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Sun layers

Page 5: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Layers of the sun

Page 6: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

• Core = where temperature exceeds fusion point (10 million Kelvin)

• Radiative Zone = nothing much goes on here. It just acts as an obstacle course for the photons created in the core and random-walking their way upward

• Convection Zone = temperature gradient is so steep that photon diffusion can’t carry the heat outward fast enough. The rising temperature expands the gas, lowering density and causing it to rise (helium-balloon-like) to the surface, where it cools, gets denser, and falls back down to get reheated and start all over again. Think – soup cooking on a stove.

• Photosphere = visible surface. This is where the mean free path now gets so long the material is transparent above here.

Page 7: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Sunspots

• Places where the sun’s magnetic field is concentrated and inhibits the normal convective flow of hot material from below. So the material sits on the surface and cools off as it radiates to the sky.

• Charged particles in a magnetic field feel a force sideways to their motion, binding the gas to the field.

• Sunspots are like “magnetic scabs” of gas unable to be recirculated to lower, hotter levels. They are bound to the magnetic fields in the photosphere, cooling as they radiate to the cold universe, and hence cool off and darken.

• Vertical structure of a sunspot

Page 8: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Sunspots optical

Page 9: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

HiRes sunspot

Page 10: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Sunspot in UV light. Hot Gas is following the magnetic field lines

Page 11: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Earth w/ sunspot

Page 12: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Plages Are Hotter Areas Near Sunspots, Where the

Energy Unable to Penetrate a Sunspot

Emerges Nearby

Page 13: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Sunspot cycle #vs time

Page 14: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Sunspot cycle 1760-1965

Page 15: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Solar Maxima have been of decreasing intensity for ~50 years

Page 16: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Helioseismology allows us to make rough predictions of the solar cycle’s intensity for a

few years in advance

Page 17: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

More Sunspots, And More Plages Too, at Solar Max

Page 18: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

How Does The Solar Cycle Affect Earth?

• Two important ways…• 1. The solar wind creates aurorae (more

later)• 2. Solar luminosity changes during the

cycle. We have seen that lower solar activity goes with lower average temperatures on Earth

Page 19: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

How Does Solar Activity Change Solar Luminosity?

• Higher solar activity produces higher solar

luminosity. • Mechanism – more surface magnetic field energy,

which thermalizes (i.e. becomes random kinetic energy, as the 2nd Law of Thermodynamics requires) and produces more net solar radiation.

• Some of the magnetic field energy directly impacts Earth by high speed solar wind particles hitting Earth.

• However, the luminosity changes are tiny; less than 0.1%, as measured by satellites above the atmosphere.

Page 20: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Satellite Data Shows TSI (Total Solar Irradiance). Note the Decreasing

Luminosity of the Sun

Page 21: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,
Page 22: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,
Page 23: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Solar Luminosity: Past 400 Yrs, from Proxies

Page 24: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

The Maunder Minimum and The “Little Ice Age” (LIA); Connected?

• The Maunder Minimum in sunspot numbers in the late 1600’s corresponds roughly to a cool period in climate on Earth.

• But detailed research finds several causes of the LIA…• 1. Unusually intense volcanic ash/dust period• 2. Disease killed ~20% of human population in the Americas,

reforestation took up extra CO2 out of the atmosphere.• 3. Lower solar luminosity (relatively minor contributor, from

satellite correlations of sunspot number vs TSI)• 4. Reduced thermohaline circulation failing to efficiently

distribute equatorial warmth to European and North American latitudes

Page 25: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

The Plague of the 1300’s is Considered a Starting Point for the Little Ice Age. There’s Another Drop in Human Population Just before Coal Discovery

Page 26: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Eclipse composite

Page 27: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Total eclipse corona

Page 28: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

cme

Page 29: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

solarwind

Page 30: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

EarthOnionMagField

Page 31: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

SOHO wide angle

Page 32: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Aurorae – GiNormous Flourescent Lights!

• Caused when high speed solar wind particles impact the Earth’s atmosphere

• Collisionally excites the nitrogen and oxygen atoms

• These atoms then de-excite (electrons fall back down through the energy levels) giving off photons

• Exactly the same as how flourescent lights work!

Page 33: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

greenpurpleAurora

Page 34: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Aurora hoffman

Page 35: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Aurora ewoldt

Page 36: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Aurora tricolor

Page 37: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Aurora from space iss

Page 38: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Long Term Solar Evolution…

• As the sun ages, its core collapses as hydrogen converts to helium, and this increases the gravity and pressure and fusion rate in the core

• So, the sun is getting more luminous on the long term

• During the 4.56 billion year life of the solar system, the sun has increased in luminosity by about 25%.

• This will continue, and gradually accelerate…

Page 39: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Long term L,R,T

Page 40: The Sun – A Typical Star The layers of the sun; core, radiative zone, convective zone, photosphere, chromosphere, and corona Sunspots and magnetic fields,

Key Points – Chap 14: The Sun and Climate

• Sun driven by fusion of H into He in core, stable with gravity balancing pressure

• Sunspots: places of strong magnetic field inhibiting convection of heat from below, cool and darken

• Sunspot cycle 11 years, with ~100 year larger cycles perhaps

• More spots = More solar activity = More solar luminosity, but only 0.1% more at max vs min

• Long term solar luminosity; has risen 30% since Birth of Earth, and will keep rising.

• Life on Earth will likely end in a billion years or so