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Chapter11 NATSReview.docx

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York University
Natural Science
NATS 1745

NATS1745 6.0 History ofAstronomy Chapter 11 Exam Review 1. What are the advantages of radio astronomy compared to visible-light astronomy? Can be detected on earth both night and day as well as through clouds. (not overwhelmed by sunlight). Easily detected with ground level telescopes (completely penetrate earth’s atmosphere). Reflect off most metallic surfaces. Not absorbed by interstellar dust. Strongly emitted by distant (young) galaxies, allowing us to observe galaxies as they appeared in the distant past. Make sure that you understand *why* radio waves have each of these advantages. 2. Who was the 1st person to detect radio emission from space? Carl Jansky was the first to detect radio emission. Where was this emission coming from? Sagittarius constellation. (Center of the galaxy) From the Milky Way disk. How did he know this? The rising and falling of the hiss every 24 hours is due to the fact that the center of the Milky Way rises and sets each day due to the Earth’s daily motion. 3. When Grote Reber mapped out the radio emission from the Milky Way, what did he find? Was able to identify a few discrete radio sources. The map showed difference between discrete radio source and the galactic hiss. The map revealed that there was a broad radio peak on the right surrounded by gradual contours. To the left of Sagittarius are two smaller peaks that indicate of other sources of radio emissions at those specific coordinates. 4. Describe the process that is producing the 21-cm radio emission in our galaxy. In a hydrogen atom, when the magnetic poles of the proton and electron are aligned, the electron eventually flips over. Since the flipped-over state is lower in energy, the electron emits a photon with energy equal to the energy difference between the two states. The hydrogen atoms naturally emit a 21-cm radio wave when their electron flips over. 5. What did maps of the 21-cm radio emission in our galaxy reveal about the structure of our galaxy? Interstellar space in our galaxy is filled with hydrogen. Our galaxy contains 4 well-defined spiral arms. We can’t see the spiral arms on the other side of the galaxy due to the shadow of the Galantic center. Proof that we are a spiral galaxy. Where is the Sun located in this structure? Resides around the arc. 6. What did Stanley Hey identify as the source of the radio emission that was interfering with British radar during WWII? Interfered by large surges of radio emission. 7. What are solar flares? Eruptions of radiation which trace out magnetic field lines from sun spots. 8. Describe how the Sun spins. It spins differentially from earth; its rotation speed decreases with latitude. Rotates around its own axis. Takes between 25-35 days to complete one rotation. Its atoms don’t all spin together. Regions close to the equator spin quickly, while regions near poles spin slowly – differential rotation. Spinning sphere of metal. How has this effected the Sun's magnetic field? Horizontal slices all spinning at different speeds due to differential rotation. Therefore, each slice has its own bar magnet, magnetic field of different strengths. Equatorial slice is strongest because rotation is fastest there. Slice at the poles is weakest in magnetic field strength. The magnetic lines will get skewed over time. What happens to the Sun's magnetic field every 11 years as a result? The twisting and untwisting of magnetic field lines every 11 years. Since it contains metal, this causes the frequency of sunspots and flares to increase every 11 years. (11 year peak solar maximum) When the twisting of the sun’s magnetic field reaches its 11-year peak, magnetic loops poke through its surface. The heat released results in sunspots. 9. What causes magnetic storms on Earth? Due to the winds of charged particles produced by sunspots. Magnetic storms – sudden scrambling of the magnetic fields. Caused by the distortion of Earth’s magnetic field by solar winds of charged particles. 10. What causes aurora on Earth? Winds of charged particles produced by sunspots.Aurora’s are the glow of charged particles from solar winds, which are interacting with the Earth’s magnetic field. (Primarily near the poles, where Earth’s magnetic field is strongest). Why are aurora most often seen at high latitudes? Most concentrated near north and south poles where Earth’s magnetic field is strongest. 11. What happens to the number and intensity of sunspots, magnetic storms and aurora every 11 years, due to the Sun's magnetic cycle? The Sun reverses its magnetic field, thus producing a cycle of storms marked by solar flares. Violent
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