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
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
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
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