MGMT 1050 Lecture Notes - Lecture 11: Richmond Hill, Ontario, Hydrogen Atom, Christian Metal

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20 Jul 2016
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NATS1745 6.0 History of Astronomy
Chapter 11 Exam Review
1. What are the advantages of radio astronomy compared to visible-light astronomy? Make sure
that you understand *why* radio waves have each of these advantages.
Advantages of radio waves:
a) Can be detected on Earth both night and day (not overwhelmed by sunlight) as well as through clouds
-unaffected by the amount of light in the sky
b) Easily detected with ground-level telescopes (they completely penetrate Earth's atmosphere)
-radiowaves are long waves, which easily pass through the atmosphere
-therefore, radio dishes don’t need to be placed at high-altitudes (can pass through the entire
atmosphere)
c) Reflect off most metallic surfaces
d) Not absorbed by interstellar dust
-Radio light from distant surfaces can make it through the dust of the milky way (because they
are long waves)
e) Strongly emitted by distant (young) galaxies, allowing us to observe galaxies as they appeared in the
distant past
-Radio emissions extent far beyond visible light
2. Who was the 1st person to detect radio emission from space? Where was this emission
coming from? How did he know this?
a) Karl Jansky
b) Our galaxy (the Milky Way)
c) Found that the strength of this noises intensity was coming from the Sagitarius constellation
3. When Grote Reber mapped out the radio emission from the Milky Way, what did he find?
Reber detected radio emission from two discrete sources
4. Describe the process that is producing the 21-cm radio emission in our galaxy.
Based on the Bohr model of the hydrogen atom:
oNucleus containing a (+ charged)proton is orbited by an (- charged) electron
oProton and electron spin around their own axis
oWhen charged particles spin, you get the magnetic field of a bar magnet
oIf the proton and electron spun is the same directions, the electron flips over (flips the
poles so that the magnetic poles are no longer aligned) because the unaligned state is more
stable
oWhen an e- flips over, it emits the energy it no longer needs
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5. What did maps of the 21-cm radio emission in our galaxy reveal about the structure of our
galaxy? Where is the Sun located in this structure?
Maps of our Galaxy's 21-cm emission, revealed its interstellar H-gas and spiral structure
oHydrogen gas is not spread uniformly throughout the galaxy (arranged in spiral arms)
The sun: found in the Orion arm (points in the direction of the orion constellation)
6. What did Stanley Hey identify as the source of the radio emission that was interfering with
British radar during WWII?
Stanley Hey detected radio emission from solar flares
7. What are solar flares?
Solar flares: eruptions of radiation which trace out magnetic field lines from sunspots
*sunspots: relatively cool spots on the sun's surface
8. Describe how the Sun spins. How has this effected the Sun's magnetic field,
and What happens to the Sun's magnetic field every 11 years as a result?
a) the Sun (a fluid) spins differentially (i.e its rotation speed decreases with latitude)
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b) As a result, its magnetic field is not a simple bar-magnet, but a complex field which twists and
untwists every 11 years
c) Every 11 years, the frequency of sunspots and flares to increase every 11 years
-As well as: the poles switching after the fields reach their “max twisted state”
9. What causes magnetic storms on Earth?
Magnetic storms: the sudden and temporary scrambling of the earth's magnetic field
-caused by the distortion of Earth’s magnetic fields by solar winds of charged particles
10. What causes aurora on Earth? Why are aurora most often seen at high latitudes?
Aurora (Northern Lights’):the glow of charged particles from solar winds which are interacting with
Earth’s magnetic field (primarily near the 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?
Increased # and intensity of sunspots: therefore increased magnetic storms and aurora because of
stronger solar winds
12. What was developed in the 1960s to extend the limits of the observable Universe in radio
light?
Radio array: Collection of radio dishes that collectively achieve the power of one giant disk
13. Describe the radio emission from a pulsar. What did Hewish initially suspect that the signal
was coming from? What is the true explanation for the pulses? Are all neutron stars
pulsars? Why/why not?
a) Pulsating radio signals following a very regular pattern were detected from the cores of supernova
remnants
b) Hewish initially though it was artificial (from extra-terrestrials; some form of communication)
c) pulsars are actually from neutron stars whose radio beams are periodically aimed at Earth
d) Not all neutron stars are pulsars because not all neutrons stars have a strong enough magnetic field
(and spinning fast enough) to release radio beams
Neutron stars (dead cores of high mass stars)
All stars spin; neutrons have a very fast spin
Spinning charged particles create magnetic fields
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