ASTR 1115G Sun Notes PDF

The Sun, Part II: Energy Transfer, Magnetic Activity and Space Weather ASTR 1115G October 1, 2024 Announcements Please put phones away, remove headphones, and put watches on DnD. Quiz due Sunday. Goal: Exam 1 graded and entered by Friday evening ...

The Sun, Part II: Energy Transfer, Magnetic Activity and Space Weather ASTR 1115G October 1, 2024 Announcements Please put phones away, remove headphones, and put watches on DnD. Quiz due Sunday. Goal: Exam 1 graded and entered by Friday evening  Anatomy of the Sun Core (Sun’s furnace) Credit: Kathleen Cantner, AGI Radiative zone Convective zone Photosphere Corona Solar Wind  The Sun’s Interior Core: Where energy is generated Radiative Zone: energy seeps through in the form of light Convective Zone: energy is transferred up in columns of hot gas Photosphere: Very thin layer that is the Sun’s “surface”. This is the only part that can be “seen” with light. Kathleen Cantner, AGI Convection and Radiation Convection occurs when heat cannot escape a hot, fluid medium because it is opaque. The outer layers of the Sun are relatively cool and hence opaque. Radiation is a very effective way to move heat, but only through media that are transparent. convective zone: radiative zone: opaque transparent sggglassmanufacturer.com  Convection credit: pricenomics  Convection credit: typesofclouds.net Cantner_SolarStructure.png Convection DKIST First Light Granulation  The Sun’s Exterior (1) Chromosphere: gas is hotter than the photosphere. Helium discovered here! (2) Transition Region: very thin, connects (1) to (3) OpenStax Astronomy (3) Corona: the part that can be seen during solar eclipses (4) Solar Wind: carries hot, charged atoms away; creates comets’ tails and is responsible for aurorae. Temperature Structure of the Sun’s Atmosphere OpenStax Astronomy Soho interactive Sun image viewer https://sohowww.nascom.nasa.gov/data/realtime/ soho/soho_fader.html Photosphere What we observe as the ‘surface’ of the Sun No sharp edge – only an optical effect We call this limb darkening Temperatures about 5600 K Only about 400 km thick! Compare to 106 km diameter! Granules about 700-1000 km in size About the size of Texas Convective cells ‘boiling’ to the surface Chromosphere Named for the bright red color seen during eclipse Thicker layer than photosphere Hotter than photosphere (~10,000 K) Helium was discovered in the chromosphere almost 30 years before it was discovered on Earth C. Witte - NASA  Outer layer of Sun’s Corona atmosphere Extends out beyond Earth! Very hot - millions of degrees K Must block out the (much) brighter photosphere to see it  Response Card Question You radiate light in the infrared with a luminosity of 100 Watts (about the same as a standard incandescent lightbulb!) The sun’s luminosity is 4x10 26 Watts. How many of you would it take to radiate as much light as the Sun? 1. 4x1024 2. 4x1028 3. 25x10-26 4. 25x1024  Response Card Question You radiate light in the infrared with a luminosity of 100 Watts (about the same as a standard incandescent lightbulb!) The sun’s luminosity is 4x10 26 Watts. How many of you would it take to radiate as much light as the Sun? 1. 4x1024 2. 4x1028 3. 25x10-26 4. 25x1024  Response Card Question Which of the following has parts of the Sun in the correct order from inner to outer layers? 1. Photosphere, radiative zone, convective zone, corona 2. Photosphere, convective zone, radiative zone, corona 3. Convective zone, radiative zone, chromosphere, photosphere 4. Radiative zone, convective zone, photosphere, chromosphere  Response Card Question Which of the following has parts of the Sun in the correct order from inner to outer layers? 1. Photosphere, radiative zone, convective zone, corona 2. Photosphere, convective zone, radiative zone, corona 3. Convective zone, radiative zone, chromosphere, photosphere 4. Radiative zone, convective zone, photosphere, chromosphere  Review Question A major difference between the Sun and Earth is: A. The Sun is much more dense than Earth; B. The Sun’s atmosphere has convection whereas Earth’s does not; C. The Sun is made mostly of hydrogen and helium whereas Earth is not; D. The Sun has a magnetic field; Earth does not.  Review Question A major difference between the Sun and Earth is: A. The Sun is much more dense than Earth; B. The Sun’s atmosphere has convection whereas Earth’s does not; C. The Sun is made mostly of hydrogen and helium whereas Earth is not; D. The Sun has a magnetic field; Earth does not.  Review Without reference to your notes, write down one method for measuring the distance to the Sun.  Sunspots B Ventrudo, B Ventrudo, oneminuteastronomer.com oneminuteastronomer.com Sunspots are regions where the Sun’s magnetic field is particularly strong. They tend to “block” convection, causing the gas in the their vicinity to cool to a lower temperature (4000 K) than the surrounding area (5600 K). They rotate with the rest of the Sun.  Review Why are the edges of granules darker than their centers?  The Solar Cycle wikipedia The number of sunspots grows and shrinks, with maxima separated by 11-year intervals. Precisely why is the subject is active inquiry, but it has to do with the evolution of magnetic fields within the Sun’s convective zone. The Solar Cycle – recent data https://www.swpc.noaa.gov/products/solar-cycle-progression The Solar Cycle – recent data https://www.swpc.noaa.gov/products/solar-cycle-progression  Magnetism in the Convective Zone Iron filings and ionized gas both move in a direction specified by the local magnetic field. What is a magnetic field? Physicists think of it V. Kaplunovsky, U. Texas Austin as invisible rubber bands threading the space around magnets that tell electrons where to go.  Flowing Charges Create Magnetism If you place a compass near a wire that has electricity going through it, you will see the compass needle deflect because moving charges create a magnetic field. The Sun is full of flowing charged matter, so it inevitably has magnetic fields too. sciathlon.blogspot.com  The smoking gun wavelength of magnetism: The Zeeman Effect Recall that energy levels of atoms take on only particular values When a magnetic field is present, these energy values can split into two close, but different energies Spectroscopy of the Sun in sunspot regions shows exactly this effect The Sun’s Magnetic Field is Complicated and Changes Constantly!  Magnetic Storms Three types of energetic events are associated with active regions in the photosphere. 1. Prominences: “loops” of hot gas that emerge above the photosphere. Tame. 2. Flares: Explosions associated with rapid release of energy stored in the magnetic fields (like snapping a rubber band). Powerful. 3. Coronal Mass Ejections: Outbursts in which hot material is ejected from the sun at 500-1000 km/s. A major source of concern. Winding of magnetic fields  Prominences SOHO-EIT Consortium/ESA/NASA via APOD  Solar Flares Flares originate in magnetically active regions associated with sunspots  Solar Flare Video https://www.youtube.com/watch?v=E8csg9YSMkk Coronal Mass Ejections credit: ESA & NASA / SOHO  Question The material ejected in Coronal Mass Ejections (CMEs) works its way toward the Earth at, say, v=1000 km/s. The typical distance from the Sun is d=1.5x10 8 km. Suppose we see the Sun send a tremendous CME toward Earth. How long (t) do we have to prepare? (Hint: d = v x t, so t = d / v). A. 1.5x105 sec (or about 41 hours) B. 1.5 sec C. 6.7x10-6 sec D. 1500 sec (about 25 minutes)  Question The material ejected in Coronal Mass Ejections (CMEs) works its way toward the Earth at, say, v=1000 km/s. The typical distance from the Sun is d=1.5x10 8 km. Suppose we see the Sun send a tremendous CME toward Earth. How long (t) do we have to prepare? (Hint: d = v x t, so t = d / v). A. 1.5x105 sec (or about 41 hours) B. 1.5 sec C. 6.7x10-6 sec D. 1500 sec (about 25 minutes) The Solar Corona Last Night SDO; composite image Solar Corona 2022 vs. 2024 SDO; composite image CMEs: Implications for Us CMEs involve enormous amounts of magnetic material hurtling toward Earth. They: Induce voltage in our electrical systems and can “fry” transformers (eg 1989 blackout in Québec) Heat up the atmosphere, increasing drag on satellites and changing their orbits; Interfere with radio communications Create static charge on satellites; Corrode oil and gas pipelines; Threaten astronauts  Takeaways The Sun’s structure consists of: core radiative zone convective zone photosphere corona The photosphere is threaded by evolving magnetic fields; these give rise to sunspots and flares and are associated with coronal mass ejections.