Transcript Unit 1

Reading
Unit 52, 53, 55
Homework 7
Unit 52 problems 4, 6, 7, 8
Unit 53 problems 5, 6, 9, 11,12
Unit 55 problems 5, 6
The Aurora
• When CME material
reaches the Earth, it
interacts with the Earth’s
magnetic field and collides
with ionospheric particles
• The collision excites
ionospheric oxygen, which
causes it to emit a photon
• We see these emitted
photons as the aurora, or
Northern Lights
The Solar Cycle
• The number of sunspots seen increases
and decreases periodically.
• Every 11 years or so, the sunspot
number peaks. This is called Solar
Maximum
• Around 5.5 years after Solar
Maximum, the sunspot number is at its
lowest level. This is called Solar
Minimum
• Solar activity (CMEs, flares, etc.)
peaks with the sunspot number
The Babcock Cycle
Differential Rotation
• Different parts of the sun rotate at different speeds
– Equator rotates faster than the poles
– Solar magnetic fields get twisted as time goes on
The Maunder Minimum
• Very few sunspots were recorded between 1645 and 1725
• This is called the Maunder Minimum
• Corresponds to relatively lower temperatures here on Earth, a
“little ice age”
• The reason for the Maunder Minimum and its effect on
climate are still unknown
Temperature and Pressure Are the Key
• In the core of the Sun, the temperature
exceeds 15 million K, and the pressure is
very high
• High temperatures imply that the nuclei in
the core are moving very fast, and the high
pressure is pushing them together
• The high speeds of the nuclei allow them to
collide and fuse via the proton-proton chain
The Proton-Proton Chain
Neutrinos
• One product (aside
from energy) of the
proton-proton chain is a
neutrino
– Very low mass, very
high energy particle
– Passes through matter
very easily, and so is
hard to detect
– Neutrino measurements
on Earth confirm our
models of fusion in the
Sun’s core
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To what do the words "hydrostatic equilibrium" in the
Sun refer?
• a. The balance of gravity inward and gas pressure
outward.
• b. The balance of gas pressure inward and heat
outward.
• c. the balance of gas pressure outward and magnetic
forces inward.
• d. the creation of one helium nucleus for the
"destruction" of every four helium nuclei.
The time taken for neutrinos generated in the
thermonuclear reactions at the center of the Sun to
escape from its surface is
• a. about 1 million years
• b. about 100,000 years
• c. instantaneous, since neutrinos travel faster than the
speed of light
• d. very short, around few seconds
What problems have observers of solar neutrino run
into?
• a. The neutrino are of the wrong type (mostly muon
neutrinos and no electron neutrinos)
• b. The neutrinos are about twice as energetic on
average than is predicted by theoretical models of the
Sun.
• c. Only about 1/3 of the expected number of neutrinos
is observed, compared to theoretical models of the
Sun.
• d. About six times as many neutrinos are observed
than expected from theoretical models of the Sun.
Solar activity reflected by the number of sunspots is
believed to influence the climate on Earth as
• A. when Sun has more sunspots it radiates less heat
• B. sunspots inhibit nuclear reactions in the Sun
• C. the number of energetic particles interacting with
Earth atmosphere changes
• D. sunspots affect the Earth orbit
Sun’s magnetism is due to
• A. iron core of the Sun
• B. heating of Corona by energetic particles generated
during Solar Flares
• C. generation of magnetic fields via fluid+magnetic
field motions
• D. neutrino flows coming from the Sun’s core
Why was adaptive optics developed?
• a. To compensate for chromatic aberration
• b. To prevent distortion of mirrors by the vacuum of
space
• c. To compensate for the image distortion caused by
the Earth atmosphere
• d. To prevent fractures of the main mirror.
The PRIMARY reason for spreading many radio
telescopes across a large area and combining the
signals at a central station (i.e. combining radio
telescopes to form an interferometer) is
• a. to produce a much sharper images of radio sources
• b. to avoid interference between signals from separate
telescopes
• c. to be able to send a more powerful signal to space
• d. ensure that cloudy weather only affects a few of
telescopes, leaving the others to continue observing
The main absorber in the atmosphere for infrared
radiation, which impedes observations of
astronomical infrared objects, is
• a. electrons in the Earth's atmosphere
• b. dust in the Earth atmosphere
• c. oxygen and nitrogen, the major constituents of the
atmosphere
• d. water vapor
Pieces of metal are heated by varying amount in a
flame. The hottest of these will be the one that shows
which color most prominently?
•
•
•
•
a. blue
b. yellow
c. red
d. black
To a physicist a blackbody is defined as an object
which
• a. absorbs all radiation which falls upon it
• b. always appears to be black, whatever its
temperature
• c. always emits the same spectrum of light, whatever
its temperature
• d. reflects all radiation which falls upon it, never
heating up and always appearing black.
The specific colors of light emitted by an atom in a
hot, thin gas are caused by
• a. protons jumping from level to level
• b. an electron dropping into the nucleus, producing
small nuclear changes
• c. electrons jumping to lower energy levels, losing
energy as they do so
• d. the vibrations of the nucleus
When electromagnetic radiation is Doppler-shifted by
motion of the source away from the detector
• a. the measured wavelength is longer than the emitted
wavelength
• b. the measured frequency of the radiation remains the
same, but its wavelength is shortened, compared to
the emitted radiation
• c. the speed of the radiation is less than the emitted
speed
• d. the measured frequency is higher than the emitted
frequency.
You see this every day!
• More distant streetlights appear
dimmer than ones closer to us.
• It works the same with stars!
• If we know the total energy output of a
star (luminosity), and we can count the
number of photons we receive from
that star (brightness), we can calculate
its distance
L
d=
4pB
• Some types of stars have a known
luminosity, and we can use this
standard candle to calculate the
distance to the neighborhoods these
stars live in.
Photons in Stellar Atmospheres
• Photons have a difficult time moving through a star’s atmosphere
• If the photon has the right energy, it will be absorbed by an atom and raise an
electron to a higher energy level
• Creates absorption spectra, a unique “fingerprint” for the star’s composition.
The strength of this spectra is determined by the star’s temperature.
Stellar Surface Temperatures
• Remember from Unit 23 that the peak
wavelength emitted by stars shifts with the
star’s surface temperatures
– Hotter stars look blue
– Cooler stars look red
• We can use the star’s color to estimate its
surface temperature
– If a star emits most strongly in a wavelength 
(in nm), then its surface temperature (T) is:
T=
2.9 ´106 K × nm
• This is Wien’s Law
l
Measuring Temperature using
Wein’s Law
T=
2.9 ´106 K × nm
l
Spectral Classification
• Around 1901, Annie
Jump Cannon
developed the spectral
classification system
– Arranges star
classifications by
temperature
• Hotter stars are O type
• Cooler stars are M
type
• New Types: L and T
– Cooler than M
• From hottest to coldest, they are
B-A-F-G-K-M
O-
– Mnemonics: “Oh, Be A Fine Girl/Guy,
Kiss Me
– Or: Only Bad Astronomers Forget
Generally Known Mnemonics