ASTR 1115G The Sun III - October 3, 2024 (PDF)

The Sun III ASTR 1115G October 3, 2024  Announcements Please (completely) put away phones Tortugas Mountain Observatory by Zoom t - Details by email Quiz due Sunday. Goal: Exam 1 graded and entered by Friday evening  Flowing Charges...

The Sun III ASTR 1115G October 3, 2024  Announcements Please (completely) put away phones Tortugas Mountain Observatory by Zoom t - Details by email Quiz due Sunday. Goal: Exam 1 graded and entered by Friday evening  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  Flares (Movie) https://www.youtube.com/watch?v=HFT7ATLQQx8  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 A B C D 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=1.5x108 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 A B C D 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=1.5x108 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) 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 The Solar Corona This Week SDO; composite image Solar Corona 2022 vs. 2024 SDO; composite image  Discussion The Sun’s “activity” level rises and Falls every 9-11 years. During this time, its overall brightness might change by 0.1%. Meanwhile, the Earth’s atmosphere has been accumulating carbon (a known greenhouse gas) since about 1800; its mean temperature has been rising steadily for over 50 years; and both are now rising unusually quickly. Can you think of a falsifiable explanation for how the solar cycle could cause Global Warming?  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.  A B Response Card Question C D Coronal Mass Ejections are caused by: A. plate tectonics on the Sun B. volcanoes distributing Solar magma C. Comets colliding with the Sun’s surface D. Magnetic activity occurring near sunspots E. Cloud formation in the chromosphere  A B Response Card Question C D Coronal Mass Ejections are caused by: A. plate tectonics on the Sun B. volcanoes distributing Solar magma C. Comets colliding with the Sun’s surface D. Magnetic activity occurring near sunspots E. Cloud formation in the chromosphere  A B Response Card Question C D Why are sunspots dark? A. they have fewer nuclear reactions than bright areas B. they indicate places where clouds have formed over the Sun C. they are places where the Sun’s photosphere is cooler D. they are places where the Sun’s composition is dominated by heavy elements  A B Response Card Question C D Why are sunspots dark? A. they have fewer nuclear reactions than bright areas B. they indicate places where clouds have formed over the Sun C. they are places where the Sun’s photosphere is cooler D. they are places where the Sun’s composition is dominated by heavy elements  A B Response Card Question C D The surface temperature of the Sun is 5800 K. If I heat up a lump of metal in a laboratory to 5800 K, it will be: A. redder than the Sun B. bluer than the Sun C. the same color as the Sun  A B Response Card Question C D The surface temperature of the Sun is 5800 K. If I heat up a lump of metal in a laboratory to 5800 K, it will be: A. redder than the Sun B. bluer than the Sun C. the same color as the Sun  Energy The Sun is the most important source of energy to life on Earth Well recognized since ancient times How could such a huge amount of energy be released? By the 19th century, conservation of energy recognized The hunt was on for where the energy could come from! Energy can change change forms but still be conserved. Case Study in Energy Conservation https://plus.nasa.gov/video/stemonstrations- kinetic-and-potential-energy/  Energy Conversion Here on Earth, we experience the conservation of energy all the time. usually between gravitational potential energy and kinetic energy If material is falling into the Sun, could the transformation of gravitational potential energy be converted into enough kinetic energy? - proposed by Kelvin & Helmholtz dreamstime.com A hypothesis for what powers the Sun Conversion of gravitational potential into thermal energy Gas particles fall towards the center of mass They gain kinetic energy (velocity) Increased kinetic energy of gas particles -> increased temperature! Only so much stuff to fall in predicts that the Sun should be about 100 million years old!  Conflicting evidence Geologists independently found that Earth must be >4 http://mspostons3rdgrade.weebly.com/fossils.html billion years old. This is was an enormous discrepancy! Gravity: 1 x 106 years Fossils: 4 x 109 years  Conflicting evidence Geologists independently found that Earth must be >4 http://mspostons3rdgrade.weebly.com/fossils.html billion years old. Solution: Nuclear Energy This is was an enormous discrepancy! Gravity: 1 x 106 years Fossils: 4 x 109 years  Atomic Nucleus Recall that electrons have a negative charge while protons have a positive charge. This means that they pull towards one another, and it explains static electricity: surfaces that have “too many” electrons will pull towards surfaces that have “too few”. It also explains why atoms can hold onto their electrons: the electrons and the protons attract! The flip-side of this effect is that surfaces that have “too many”electrons (more electrons than protons) will repel each other.  Atomic Nucleus In 1911, it was discovered that all of a gold atom’s positive charge is concentrated into a tiny nucleus. This was a big surprise! It implies the existence of a strong nuclear force. The idea is that, although protons do repel each other through the electrostatic force, if they get very close, then they attract each other through the much stronger strong force, which can make protons stick together as long as they’re already very close. It’s sort of like glue.  Atomic Nucleus So there is always this tension between the strong force, which tries to keep nuclei together, and the electrostatic force, which tries to make them fly apart. As it turns out, although the strong force is strong, it can’t keep two protons stuck together for long. Neutrons (discovered in 1932) have the same mass as protons but no charge. They provide the extra strong force glue to keep heavy nuclei energetically bound.  Atomic Nucleus The number of protons and electrons entirely determines an atom’s chemical properties (that is, how it forms molecules with other atoms). The number of neutrons determines how stable its nucleus is: if a nucleus has too few or too many neutrons, then it will decay radioactively. Take a breather…  Isotope Notation Used to indicate mass (top number: nucleons = protons + neutrons) and atomic number (bottom number: the number of protons) in a nucleus. 1 1 H This hieroglyphic describes a nucleus that has 1 nucleon, and one proton. So evidently there are no neutrons. This is ordinary hydrogen. H 2 1 This describes a nucleus that has 2 nucleons, and one is a proton. So evidently there is one neutron. This is “deuterium” or “heavy hydrogen”. It occurs naturally, but is poisonous in large quantities.  Isotope Notation 14C 6 This describes a nucleus that has 14 nucleons, and 6 of them are protons. This is “carbon 14”, which is radioactive. 12C 6 This describes a nucleus that has 12 nucleons, and 6 are protons. So evidently there are 6 neutrons. This is ordinary carbon. Here is carbon 13, which is also stable: 13C 6