Next quiz: Monday, October 31 Focus on Chapter 8 1
The Sun as a Star (Chp. 8) 2
Sun is 109 times larger than Earth (about 10 times larger than Jupiter. Its surface temperature is 5800 K and it radiates most of its energy in the optical (near yellow). The is made of 92% Hydrogen, 7.8% Helium, and 0.2% everything else. Atmosphere has three regions: photosphere, chromosphere, and corona. Sunspots are cooler than surrounding atmosphere Sunspots are regions of concentrated magnetic field Currents in the Sun produce magnetic fields; differential rotation tangles them up, producing active regions. Active regions have many names, depending on where/ how we see them: sunspots, plages, prominences (flares & coronal mass ejections too). 3
Solar Cycle The number of sunspots varies in an 11 year cycle Each sunspot peak is called a solar maximum 4
Solar Cycle The number of sunspots varies in an 11 year cycle Each sunspot peak is called a solar maximum 4
Butterfly Diagram Sun spot cycle starts out with spots at higher latitudes on the sun. Evolve to lower latitudes (towards the equator) throughout the cycle 5
Maunder Minimum 1645-1715: extended lull in solar activity Little Ice Age recorded in Europe 6
Sun-quakes!! 7
What Powers the Sun? 8
Early Ideas The Sun is a ball of fire. Problem #1: A lump of coal the size of the Sun would burn out in about 5000 years. Problem #2: Temperatures involved are much too high for common fire which is a chemical process involving the electrons orbiting molecules. 9
Early Ideas (cont) Gravity compresses interior of Sun to extreme temperatures. If you descend down a mine shaft, you ll notice that the temperature begins to INCREASE with depth (below about 20 m depth). 10
Early Ideas (cont) Gravity compresses interior of Sun to extreme temperatures. Problem #1: Sun is constantly losing energy. To keep it shining with a steady brightness, it would have to keep shrinking. Problem #2: Whole process would take about 10 million years. 11
Modern Ideas 1905: Einstein s Theory of General Relativity Energy can be created from mass and vice-versa. All mass has an equivalent of amount of energy which is given by the formula: E=mc 2 For example: the mass in an aspirin is equivalent to a small nuclear weapon. How does the conversion take place? - subatomic (nuclear) reactions - process called fusion - example: Proton-Proton Chain 12
Review: Isotopes 13
Requires very high temperatures (greater than 10 million K)! 14
How long can the Sun keep shining? 15
Proton-Proton Chain (cont) What you put in (net): 4 hydrogen atoms (protons) What you get out (net): 1 helium atom (2 protons and 2 neutrons) 16
Proton-Proton Chain (cont) What you put in (net): 4 hydrogen atoms (protons) mass= 6.693 10-24 grams What you get out (net): 1 helium atom (2 protons and 2 neutrons) mass= 6.645 10-24 grams 16
Proton-Proton Chain (cont) What you put in (net): 4 hydrogen atoms (protons) mass= 6.693 10-24 grams What you get out (net): 1 helium atom (2 protons and 2 neutrons) mass= 6.645 10-24 grams Mass Deficit: 0.048 10-24 grams (or 0.7%) 16
Proton-Proton Chain (cont) Only 0.7% of the mass is converted into energy! Fortunately, the Sun has a lot of mass! Unfortunately, only the innermost 10% is hot enough for fusion to take place 17
How much mass will be converted into energy? Mass of Sun = 2.0x10 33 grams 18
How much energy is that? Energy = mc 2 = 1.3 10 51 ergs Funny energy units! 19
Sun is losing 3.9x10 33 ergs of energy every second! How long can it keep this up?! Total Energy Available = 1.3 10 51 ergs Every second, Sun emits 3.9 10 33 ergs 20
Sun is losing 3.9x10 33 ergs of energy every second! How long can it keep this up?! Total Energy Available = 1.3 10 51 ergs Every second, Sun emits 3.9 10 33 ergs 3.3 10 17 seconds = 10 billion years! 20
Chapter 19 The Origin of the Solar System
Outline I. Theories of Earth s Origin A. Early Hypotheses B. The Solar Nebula Hypothesis II. A Survey of the Solar System A. A General View B. Two Kinds of Planets C. Space Debris D. The Age of the Solar System
Outline (continued) III. The Story of Planet Building A. A Review of the Origin of Matter B. The Chemical Composition of the Solar Nebula C. The Condensation of Solids D. The Formation of Planetesimals E. The Growth of Protoplanets F. Is There a Jovian Problem? G. Explaining the Characteristics of the Solar System H. Clearing the Nebula IV. Planets Orbiting Other Stars A. Planet-Forming Disks around Other Suns B. Extrasolar Planets
Early Hypotheses Catastrophic hypotheses predict: Only few stars should have planets! catastrophic hypotheses, e.g., passing star hypothesis: Star passing the sun closely tore material out of the sun, from which planets could form (no longer considered) evolutionary hypotheses, e.g., Laplace s nebular hypothesis: Evolutionary hypotheses predict: Most stars should have planets! Rings of material separate from the spinning cloud, carrying away angular momentum of the cloud cloud could contract further (forming the sun)
The Solar Nebula Hypothesis Basis of modern theory of planet formation. Planets form at the same time from the same cloud as the star. Planet formation sites observed today as dust disks of T Tauri stars. Sun and our Solar system formed ~ 5 billion years ago.
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Survey of the Solar System 29
Mnemonic to help you remember the order of the planets in the solar system: My Very Excited Mother Just Served Us Nine Pizzas Just Sat Upon Nine Pins 30
Mnemonic to help you remember the order of the planets in the solar system: My Very Excited Mother Just Served Us Nine Pizzas Just Sat Upon Nine Pins 30
Mnemonic to help you remember the order of the planets in the solar system: My Very Excited Mother Just Served Us Nine Pizzas Just Sat Upon Nine Pins My Very Excited Mother Just Served Us Nachos 30
Survey of the Solar System Relative Sizes of the Planets Assume, we reduce all bodies in the solar system so that the Earth has diameter 0.3 mm. Sun: ~ size of a small plum. Mercury, Venus, Earth, Mars: ~ size of a grain of salt. Jupiter: ~ size of an apple seed. Saturn: ~ slightly smaller than Jupiter s apple seed. Pluto: ~ Speck of pepper.
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Planetary Orbits Mercury Venus Earth Mars Jupiter Saturn All planets in almost circular (elliptical) orbits around the sun, in approx. the same plane (ecliptic). Sense of revolution: counterclockwise Sense of rotation: counterclockwise (with exception of Venus, Uranus, and Pluto) (Distances and times reproduced to scale) Uranus Orbits generally inclined by no more than 3.4 o Exceptions: Mercury (7 o ) Pluto (17.2 o ) Pluto Neptune
Planetary Orbits Mercury Venus Earth Mars Jupiter Saturn All planets in almost circular (elliptical) orbits around the sun, in approx. the same plane (ecliptic). Sense of revolution: counterclockwise Sense of rotation: counterclockwise (with exception of Venus, Uranus, and Pluto) (Distances and times reproduced to scale) Uranus Orbits generally inclined by no more than 3.4 o Exceptions: Mercury (7 o ) Pluto (17.2 o ) Pluto Neptune
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Inclination and Obliquity 37