DOC PREVIEW
UMD ASTR 100 - Introduction to Astronomy Our Star

This preview shows page 1-2-3-4-30-31-32-33-34-61-62-63-64 out of 64 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 64 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

ASTR100 (Spring 2008) Introduction to Astronomy Our StarWhy does the Sun shine?LuminosityPowerPoint PresentationSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Quiz!What is the Sun’s structure?Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29How does nuclear fusion occur in the Sun?Slide 31Slide 32Slide 33Slide 34Thought QuestionSlide 36Solar ThermostatHow does the energy from fusion get out of the Sun?Slide 39Slide 40Slide 41How do we know what is happening inside the Sun?Slide 43Slide 44Slide 45Slide 46Slide 47What causes solar activity?Solar activity is like “weather”…Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57How does solar activity affect humans?Slide 59Slide 60Slide 61How does solar activity vary with time?Slide 63Slide 64ASTR100 (Spring 2008) Introduction to AstronomyOur StarProf. D.C. RichardsonSections 0101-0106Why does the Sun shine?Lifetime =Total EnergyLuminosity• This helps explain why the Sun shines!…LuminosityLuminosity is light energy emitted per unit time.Measured in Watts (Joules per second).Our Sun’s luminosity is 3.8 × 1026 W.That’s a lot of 100-W lightbulbs!!Is it on FIRE?Is it on FIRE? Luminosity ~ 10,000 yearsChemical Energy ContentIs it on FIRE? … NO! Luminosity ~ 10,000 yearsChemical Energy ContentIs it CONTRACTING?LuminosityGravitational Potential EnergyIs it CONTRACTING?~ 25 million yearsLuminosityGravitational Potential EnergyIs it CONTRACTING? … NO!~ 25 million yearsIs it powered by NUCLEAR ENERGY?Is it powered by NUCLEAR ENERGY?E = mc2- Einstein, 1905Is it powered by NUCLEAR ENERGY?Luminosity~ 10 billion yearsNuclear Potential Energy (core)E = mc2- Einstein, 1905Is it powered by NUCLEAR ENERGY? … YES!Luminosity~ 10 billion yearsNuclear Potential Energy (core)E = mc2- Einstein, 1905The Sun is in gravitational equilibrium…The outward push of pressure balances the inward pull of gravity.Weight of upper layers compresses lower layers.Gravitational equilibrium…Energy provided by fusion (heat) maintains the pressure.Gravitational contraction…Provided energy that heated core as Sun was forming.Contraction stopped when fusion began.Quiz!Consider Schrödinger’s equation:Show that this equation is equivalent to:Haha! April Fools!What is the Sun’s structure?Radius: 6.9 x 108 m (109 times Earth)Mass: 2 x 1030 kg (300,000 Earths)Luminosity: 3.8 x 1026 WattsSolar wind:A flow of charged particles from the surface of the Sun.Corona:Outermost layer of solar atmosphere. ~1 million KChromosphere:Middle layer of solar atmosphere.~ 104–105 KPhotosphere:Visible surface of Sun.~ 6,000 KConvection Zone:Energy transported upward by rising hot gas.Radiation Zone:Energy transported upward by photons (light).Core:Energy generated by nuclear fusion.~ 15 million KHow does nuclear fusion occur in the Sun?FissionBig nucleus splits into smaller pieces.(Nuclear power plants)FusionSmall nuclei stick together to make a bigger one.(Sun, stars)High temperature enables nuclear fusion to happen in the core.(Atoms move faster when they’re hotter.)The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus in several steps.The sequence of steps is called the proton-proton chain.IN4 protonsOUT4He nucleus2 gamma rays2 positrons2 neutrinosTotal mass is 0.7% lowerE = mc2Thought QuestionWhat would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?A. The core would expand and heat up slightly.B. The core would expand and cool.C. The Sun would blow up like a hydrogen bomb.Thought QuestionWhat would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?A. The core would expand and heat up slightly.B. The core would expand and cool.C. The Sun would blow up like a hydrogen bomb.Solar thermostat keeps burning rate steadySolar ThermostatDrop 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.How does the energy from fusion get out of the Sun?Energy gradually leaks out of the radiation zone in the form of randomly bouncing photons.Convection (rising hot gas) takes energy to surface.Bright blobs on photosphere are where hot gas reaches the surface.How do we know what is happening inside the Sun?We learn about the inside of the Sun by…Making mathematical models.Observing “sunquakes”.Observing solar neutrinos.Patterns of vibration on the surface tell us what the Sun is like inside.Results agree very well with mathematical models of the solar interior.Neutrinos created during fusion fly directly through the Sun.Observations of these solar neutrinos can tell us what’s happening in core.Solar neutrino problem:Early searches for solar neutrinos failed to find the predicted number.Solar neutrino problem:Early searches for solar neutrinos failed to find the predicted number.More recent observations find the right number of neutrinos, but some have changed form.What causes solar activity?Solar activity is like “weather”… Sunspots.Solar prominences.Solar flares.Coronal mass ejections.All are related to magnetic fields.SunspotsCooler than other parts of the Sun’s surface (4000 K).Regions with strong magnetic fields.Click me!Charged particles spiral along magnetic field lines.Loops of bright gas often connect sunspot pairs (prominence).Click me!Loops trace magnetic field lines.Click me!Magnetic activity causes solar flares that send bursts of X-rays and charged particles into space.Click me!Magnetic activity also causes solar prominences that erupt high above the Sun’s surface.The corona appears bright in X-ray photos in places where magnetic fields trap hot gas.How does solar activity affect humans?Coronal mass ejections send bursts of energetic charged particles out through the solar system.Click me!Charged particles streaming from Sun can disrupt electrical power grids and disable communications satellites.Energetic particles high in Earth’s atmosphere cause aurorae (e.g., Northern Lights).How does solar activity vary with time?Number of sunspots rises and falls in 11-year cycle.Click me!Sunspot cycle related to winding and twisting of Sun’s magnetic


View Full Document

UMD ASTR 100 - Introduction to Astronomy Our Star

Download Introduction to Astronomy Our Star
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Introduction to Astronomy Our Star and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Introduction to Astronomy Our Star 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?