A105 Stars and Galaxies  News Quiz Today  Review Exam 1  Homework 6 (the Sun) due Thursday Today’s APODAPOD

Announcements… Solar Lab today at 11, tomorrow at 2 PM Kirkwood Obs. Moon Festival, Oct. 4, 8:30-10:30 Rooftop Session, Oct. 4, 9:00 Orionid meteor shower, Oct , just before midnight

Exam Review Range of score: of 80 questions Average score: 54/80 NovaSearch I Homework If you picked a year with just a few observations available, you will need to select another year with more for NS II and NS III! If the year you selected did not seem to show any blemishes, view some other years to see what they look like.

News Quiz On a piece of paper, list three important ideas from this week’s audio selection Print your name carefully – if we can’t read your writing, we can post the points to the gradebook!

The Sun Today Image credit: Solar Orbiting Heliospheric Observatory/MDI

Basic Facts radius 7 x 10 5 km about 100 x Earth’s radius mass = about 300,000 x Earth’s mass distance 1 AU, 8 light minutes 1.5 x 10 8 km about 100 x Sun’s diameter Temperature about 6000 Kelvin (10,000 F) at the surface about 15 million Kelvin inside Composition 90% of atoms are hydrogen 10% of atoms are helium WHY WE STUDY THE SUN The Sun

Helioseismology With helioseismology, we can measure temperature, pressure and motion inside the Sun from sound waves that traverse the Sun’s interior.

Listen to the Sun The Sun oscillates in complex patterns over the whole interior and surface. The frequency and location of the oscillations give us a detailed picture of the inside of the Sun. Helioseismology blue = inward motion red = outward motion

Basic Structure INSIDE Core Radiative Zone Convection Zone OUTSIDE Photosphere Chromosphere Corona Solar Wind

Conditions inside the Sun Temperature peaks in the core and drops off at the outside edge of the Sun

Why does the Sun Shine? The Sun is a “cooling ember” The Sun is burning like coal or wood The Sun is contracting due to gravity NONE OF THESE PRODUCES ENOUGH ENERGY

NUCLEAR REACTIONS produce enough energy Luminosity ~ 10 billion years Nuclear Potential Energy (core) E = mc 2 - Einstein, 1905

Fission: Big nucleus splits into smaller pieces Fusion: Small nuclei stick together to make a bigger one What produces nuclear energy?

The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus Nuclear fusion requires high temperatures and high density

The Sun’s Energy Comes from Nuclear Fusion The Conversion of hydrogen into helium

Proton-proton chain fuses hydrogen into helium IN: 4 protons OUT: 4 He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower The missing mass is converted to energy Rate of nuclear fusion depends on temperature

Neutrinos created during fusion fly directly out of the Sun These neutrinos can be detected on Earth How do we know nuclear reactions are going on in the Sun?

Estimating the Sun’s Lifetime How much fuel does the Sun have? How fast is that fuel being consumed? When will it run out? The Sun’s Lifetime

How much fuel? The Sun “burns” hydrogen to helium in a nuclear reaction How many hydrogen atoms in the Sun –2 x grams of hydrogen –6 x atoms in each gram E = mc 2 12 x hydrogen atoms

How Much Energy Can the Sun Produce? For each helium nucleus created, the Sun produces 5 x joules of energy –the Sun can burn half its hydrogen –FOUR hydrogen atoms are needed to make each helium atom E = mc 2 ½ x ¼ x 12x10 56 x 5x = 7 x joules

How Much Energy Each Second? –At the distance of the Earth, the Sun radiates 1400 watts (1400 joules per second) in each square meter on the surface of a sphere with a radius equal to one AU –How many square meters are on that sphere? The Solar Constant 1 meter 1400 watts = watt light bulbs What is a joule? Each second a 100-watt light bulb produces 100 joules of energy

Sphere with radius of 1 AU Surface area of a sphere = 4  r 2 How many square meters on a sphere with radius one AU? Area times energy per square meter per second equals total energy output per second The Sun produces 4 x watts

Solar Energy From the conversion of hydrogen into helium by nuclear reactions… E = mc 2 How long will the Sun shine??? Total energy available = 7 x joules Radiating energy at 4 x joules per second Lifetime =7 x joules 4 x joules per second = 2 x seconds = 6 x years

Solar Energy In fact, the Sun will only shine for about 10 billion years, twice its present age. E = mc 2 How long will the Sun shine??? Not all the Sun’s hydrogen is in regions hot enough for hydrogen fusion reactions to occur. We’ll learn more about the future evolution of the Sun as we look more closely at other stars in the Galaxy.

Radiation Convection How does the energy from fusion get out of the Sun?

Radiation: In the inner regions of the solar interior, energy gradually leaks upward in form of randomly bouncing electromagnetic waves. Further from the center, the wavelengths of the electromagnetic waves become longer.

Energy Transport In the outer regions of the Sun’s interior, energy flows outward by convection; heat is carried upward by bubbling hot gas.

The convection zone gives the surface the appearance of boiling liquid

Gravitational contraction: Provided energy that heated core as Sun was forming Contraction stopped when fusion began Gravitational equilibrium: Energy provided by fusion maintains the pressure Balancing Gravity

Solar Thermostat Decline in core temperature causes fusion rate to drop, so core contracts and heats up Rise in core temperature causes fusion rate to rise, so core expands and cools down

Summary: Why was the Sun’s energy source a major mystery? –Chemical and gravitational energy sources could not explain how the Sun could sustain its luminosity for more than about 25 million years Why does the Sun shine? –The Sun shines because gravitational equilibrium keeps its core hot and dense enough to release energy through nuclear fusion.

The Budget of Solar Radiation percent Reflected back out to space35% Absorbed by atmosphere18% Scattered to the Earth from blue sky10% Scattered to the Earth from clouds14% Hits the Earth's surface directly23% 100% What happens to sunlight that falls on the Earth?

Recall the structure of the Sun…

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

 The Sun! Units 49, 50, 52  Homework 6 Due THURS. SOLAR LAB TODAY AT 11:00, TOMORROW AT 2:00