Today: Chapter 10 Reading Next Week: Homework Due March 12 Midterm Exam: March 19 Correction to Homework #1: Diameter of eye: 2.5 cm #10: See Ch. 11 Office Hours Monday. 11AM -2 PM Help Sessions Available: See class website.
The Outer Parts of the Sun The outer layers of the Sun are called the Sun s Atmosphere. It is usually divided into the 3 layers.! The photosphere is the layer we see! The chromosphere is just above the photosphere! The corona is the outermost part of the Sun.
Convection & Granulation Gas in the Sun is undergoing convection. Cells of hot gas are bubbling up in the Convection Zone The gas then cools and sinks down. The top of the convection zone is called the photosphere of the Sun. Each bubble is about 700 km across.
The Photosphere Is the apparent surface layer of the Sun Light from the interior leaves the Sun at the Photosphere Temperature 5800 K The Chromosphere is a thin layer above the Photosphere Image JulioC
Chromosphere seen Total Solar Eclipse Aug. 21, 2017
The Chromosphere has Prominences, which erupt of the Sun s Surface
The Corona! Outside the chromosphere is the Sun s Corona! Its temperature is even hotter than the photosphere: 1 million Kelvins.! But, it has low density.! Because it is so hot, it emits X rays! It has streamers that follow magnetic field lines
Sun s corona seen on August 21, 2017 (c) James Van Zandt, 2017
The Sun s Corona looks different every eclipse... 1916 2005 2017 NASA
Solar Wind The corona expands outwards, becoming the solar wind A Solar Flare can bombard the Earth with high-energy particles. Sun Coronal Mass Ejection moves out at 4 million M.P.H.!
Eruption on the Sun seen in Ultraviolet light.
Anim. Such a solar storm could endanger astronauts. Fortunately, Earth s magnetic field deflects the particles. They strike Earth at the North & South Poles.
! When they strike the Earth s atmosphere, they produce the Aurora Borealis, the Northern Lights. Image from: http://astroguyz.com/
Oct. 2016 Aurora over Iceland
check: spaceweather.com for reports on solar flares & aurorae
Sun s Magnetic Field! Like the Earth, the Sun has a Magnetic Field.! As the Sun rotates, its magnetic field lines become twisted.! When they reach the surface of the Sun, they emerge as sunspots.! Sunspots appear on the Sun, and last for a few weeks.! The number of spots on the Sun changes from day to day. A sunspot
Sunspots are cooler regions of the photosphere (T 4240 K).
Sunspot image from SOHO satellite visible
Solar Activity Cycle! The sunspot cycle: every 11 years the number of sunspots increases! Every 11 years the north and south magnetic poles reverse! Number of spots reach a Maximum in ~2014 ; the poles reversed!! We are now at Solar Minimum (no spots)
The 11-year sunspot cycle has been observed for centuries. However, from 1645 to 1715, very few sunspots were observed. This lack of spots is called the Maunder Minimum On Earth, extreme cold temperatures were reported...
The Interior of the Sun! All solar energy is generated in the core! The core is about 10% of the Sun s diameter! The temperature of the core is about 15 million K!! It also has very high density.! Under these conditions, nuclear reactions occur, which power the Sun.
Energy from the Sun! Chemical reactions (like fire, metabolism) involve an atom s electrons. Eg.! 2 H2 + O2 = 2 H2O! Nuclear reactions involve an atom s nucleus...! They are much more powerful.! They create new elements!! All of the Sun s energy comes from nuclear reactions.! (so the Sun is not on fire )! Since the Sun is mostly made of Hydrogen (H), the reactions involve H nuclei.
Energy from the Sun! Atoms in the Sun s core have lost their electrons. (they are ionized) Atom Ion! A Hydrogen nucleus = 1 proton! If four Hydrogen nuclei come together, they can fuse, forming a Helium nucleus.! This fusion reaction creates a tremendous amount of energy
Fusion in the Sun! For Fusion to happen, 4 Hydrogen nuclei (protons) must combine to become Helium! But Helium has 2 protons and 2 neutrons.! Can protons turn into neutrons?!... Only if they also produce a positively charged particle.! Positive electrons, called positrons are an example of antimatter!! The sequence of steps to produce Helium is called the proton-proton chain
The Proton-Proton Chain positron (antimatter!) photon (light energy)
Energy from the Sun: Nuclear Fusion Start with: 4 Hydrogen nuclei End up with: 1 Helium nucleus 4 Hydrogens weigh more than one Helium.
Where Stars Get Their Energy! The end product of nuclear fusion is the Helium nucleus! This Helium is about 1% lighter than the 4 Hydrogens that made it up.! (exact factor: 0.007 = 0.7 % )! Where did that mass go?! Albert Einstein discovered that mass (m) can transform into energy (E).! c is the speed of light E =mc 2! c = 3 x 10 8 m/s so c 2 = 9 x 10 16 m 2 /s 2!!!!!! A small amount of mass can produce a lot of energy
Energy from Mass Example! When Hydrogen fuses into Helium, 1% of the mass becomes energy.! Question: If 1 gram of matter disappears, how many Joules of Energy will be produced.!! 1 Joule = kg m 2 / s 2. (eg: a 100 Watt light emits 100 Joules per second)! In nuclear reactions, mass is converted into energy E =Mc 2 M is the mass lost. (not the total mass), in kilograms (kg) E is the Energy produced, in Joules (J)! M =1 gram = 0.001 kg c 2 = 9 x 10 16 m 2 /s 2 (Note: use m/s here!)
E =Mc 2 E = (0.001 kg) x ( 9 x 10 16 m 2 /s 2 ) E = 9 x 10 13 kg m 2 / s 2 = 9 x 10 13 Joules of energy This is equal to the energy:! of burning 1 million gallons of gasoline!! exploding 25,000 tons of dynamite (25 kilotons of TNT) All from one gram of mass disappearing!
Nuclear Fusion in the Sun! The Sun converts 4 million tons of matter to energy every second!! This energy is equal to 2 billion hydrogen bombs! (1 Hydrogen bomb ~ 2 Megatons of TNT)! The Sun has been shining for 5 billion years, all this time converting Hydrogen to Helium.! Fortunately, the Sun has enough Hydrogen fuel to keep shining for 5 billion more years.
Nuclear Power can be generated two ways: Fission Fusion! Breaking up a big nucleus, (like Uranium) to produce smaller nuclei (like Lead)! Combining small nuclei (like Hydrogen) to form larger (like Helium) Both types have been used by people here on Earth.