Download Linking Asteroids and Meteorites through Reflectance

Astronomy 101
The Solar System
Tuesday, Thursday
Tom Burbine
[email protected]
Course
• Course Website:
– http://blogs.umass.edu/astron101-tburbine/
• Textbook:
– Pathways to Astronomy (2nd Edition) by Stephen Schneider
and Thomas Arny.
• You also will need a calculator.
• There is an Astronomy Help Desk that is open
Monday-Thursday evenings from 7-9 pm in Hasbrouck
205.
• There is an open house at the Observatory every
Thursday when it’s clear. Students should check the
observatory website before going since the times may
change as the semester progresses and the telescope
may be down for repairs at times. The website is
http://www.astro.umass.edu/~orchardhill/index.html.
HWs #6, #7, #8, and #9
• Due by Feb. 23rd at 1 pm
Exam #2
• February 25th
• Covers from last exam up to today
Sun
• Brightest star in the sky
• Closest star to Earth
• Next Closest is Alpha Centauri, which is 4.3 light
years away
Sun video
• http://www.space.com/common/media/video/play
er.php?videoRef=sun_storm
Solar Constant
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Energy received at Earth’s distance from the Sun
~1400 W/m2
50-70 % reaches Earth’s surface
30% absorbed by atmosphere
0-20% reflected away by clouds
http://en.wikipedia.org/wiki/File:Sun_Life.png
Absorption lines
Energy Source for Sun
• Fusing hydrogen into helium
– Hydrogen nucleus – 1 proton
– Helium nucleus – 2 protons, 2 neutrons
• Need high temperatures for this to occur
• ~10 to 14 million degrees Kelvin
http://www.astronomynotes.com/starsun/s3.htm
http://www.astronomynotes.com/starsun/s3.htm
How does Fusion Convert Mass to
Energy
• What is the most famous formula in the world?
E = mc2
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m is mass in kilograms
c is speed of light in meters/s
E (energy) is in joules
very small amounts of mass may be converted
into a very large amount of energy
Law
• Law of Conservation of mass and energy
– Sum of all mass and energy (converted into the same
units) must always remain constant during any
physical process
0.993 kg
1 kg
1 kg
0.993 kg
0.007 kg
http://observe.arc.nasa.gov/nasa/exhibits/stars/star_6.html
Reaction
• 4 protons → helium-4 + 2 neutrinos + energy
Neutrino-virtually massless, chargeless particles
Positron-positively charged electron – annihilated immediately by
colliding with an electron
to produce energy
Antiparticles
• Antiparticle – particle with the same mass and
opposite electric charge
• Antiparticles make up antimatter
• Annihilation – when a particle and an antiparticle
collide
• Antimatter is said to be the most costly substance
in existence, with an estimated cost of $62.5
trillion per milligram.
Fusion reaction
• Much more complicated than
4 protons → helium-4 + 2 neutrinos + energy
Deuteron – Deuterium
(hydrogen with a neutron)
nucleus
Proton-Proton Chain Reaction
• This reaction occurs ~1038 times each second
• It if occurred faster, Sun would run out of fuel
Neutrinos
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Neutrinos – almost massless particles
No charge
It takes a neutrino about 2 seconds to exit the Sun
The neutrino was first postulated in 1930 by Wolfgang
Pauli to preserve conservation of energy, conservation of
momentum, and conservation of angular momentum
during the decay of a neutron into a proton where an
electron is emitted (and an antineutrino).
• Pauli theorized that an undetected particle was carrying
away the observed difference between the energy,
momentum, and angular momentum of the initial and
final particles.
How was the Homestake Gold Mine used
to detect neutrinos?
• A 400,000 liter vat of chlorine-containing cleaning fluid
was placed in the Homestake gold mine
• Every so often Chlorine would capture a neutrino and
turn into radioactive argon
• Modelers predict 1 reaction per day
• Experiments found 1 reaction every 3 days
• Newer detectors used water
to look for reactions
What was the solar neutrino problem?
• Less neutrinos appeared to have been produced
from the Sun than expected from models
Solution of Problem
• Neutrinos come in three types (slightly different
masses)
– Electron neutrino
– Muon neutrino
– Tau Neutrino
• Experiment could only detect electron neutrinos
• Fusion reactions in Sun only produced electron
neutrinos
• Electron neutrinos could change into other types
of neutrinos that could not be detected
• Neutrino oscillations – one type of neutrino could
change into another type
Fusion
• The rate of nuclear fusion is a function of
temperature
• Hotter temperature – higher fusion rate
• Lower temperature – lower fusion rate
• If the Sun gets hotter or colder, it may not be good
for life on Earth
What is happening to the amount of
Helium in the Sun?
• A) Its increasing
• B) its decreasing
• C) Its staying the same
What is happening to the amount of
Helium in the Sun?
• A) Its increasing
• B) its decreasing
• C) Its staying the same
So how does the Sun stay relatively
constant in Luminosity
(power output)
http://www-ssg.sr.unh.edu/406/Review/rev8.html
Figure 15.8
Figure 15.4
Temperature
Density
Parts of Sun
Core
• Core – 15 million Kelvin – where fusion occurs
Figure 15.4
Radiation zone
• Radiation zone – region where energy is
transported primarily by radiative diffusion
• Radiative diffusion is the slow, outward migration
of photons
Figure 15.13
Photons emitted from Fusion reactions
• Photons are originally gamma rays
• Tend to lose energy as they bounce around
• Photons emitted by surface tend to be visible
photons
• Takes about a million years for the energy
produced by fusion to reach the surface
Figure 15.4
Convection Zone
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Temperature is about 2 million Kelvin
Photons tend to be absorbed by the solar plasma
Plasma is a gas of ions and electrons
Hotter plasma tends to rise
Cooler plasma tends to sink
Figure 15.14
Granulation – bubbling pattern due to convection
bright – hot gas, dark – cool gas
Figure 15.14
Figure 15.10
Figure 15.4
Classification of Stars
• Stars are classified according to luminosity and
surface temperature
• Luminosity is the amount of power it radiates into
space
• Surface temperature is the temperature of the
surface
Stars have different colors
Surface Temperature
• Determine surface temperature by determining the
wavelength where a star emits the maximum
amount of radiation
• Surface temperature does not vary according to
distance so easier to measure
1913
Who were these people?
• These were the women (called computers) who
recorded, classified, and catalogued stellar spectra
• Were paid 25 cents a day
• Willamina Fleming (1857-1911) classified stellar
spectra according to the strength of their hydrogen
lines
• Classified over 10,000 stars
Fleming’s classification
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A - strongest hydrogen emission lines
B - slighter weaker emission lines
C, D, E, … L, M, N
O - weakest hydrogen lines emission lines
Annie Jump Cannon (1863-1941)
• Cannon reordered the classification sequence by
temperature and tossed out most of the classes
• She devised OBAFGKM
More information
• Each spectral type had 10 subclasses
• e.g., A0, A1, A2, … A9 in the order from the
hottest to the coolest
• Cannon classified over 400,000 stars
OBAFGKM
• Oh Be A Fine Girl/Gal Kiss Me
• http://www.mtholyoke.edu/courses/tburbine/ASTR223/O
BAFGKM.mp3
http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap04/FG04_05.jpg
http://spiff.rit.edu/classes/phys301/lectures/spec_lines/spec_lines.html
http://scope.pari.edu/images/stellarspectrum.jpg
But
• absorption line - A dark feature in the spectrum
of a star, formed by cooler gas in the star's outer
layers (the photosphere) that absorbs radiation
emitted by hotter gas below.
Cecilia Payne-Gaposchkin (1900-1979)
• Payne argued that the great variation in stellar
absorption lines was due to differing amounts of
ionization (due to differing temperatures), not
different abundances of elements
Cecilia Payne-Gaposchkin (1900-1979)
• She proposed that most stars were made up of
Hydrogen and Helium
• Her 1925 PhD Harvard thesis on these topics was
voted best Astronomy thesis of the 20th century
It takes progressively more energy to remove successive electrons from an atom.
That is, it is much harder to ionize electrons of He II than He I.
Hertzsprung-Russell Diagram
• Both plotted spectral type (temperature) versus
stellar luminosity
• Saw trends in the plots
• Did not plot randomly
Remember
• Temperature on x-axis (vertical) does from higher
to lower temperature
• O – hottest
• M - coldest
Hertzsprung-Russell Diagram
• Most stars fall along the main sequence
• Stars at the top above the main sequence are
called Supergiants
• Stars between the Supergiants and main sequence
are called Giants
• Stars below the Main Sequence are called White
Dwarfs
wd
white dwarfs
• giant – a star with a radius between 10 and 100
times that of the Sun
• dwarf – any star with a radius comparable to, or
smaller than, that of the Sun
Classifications
• Sun is a G2 V
• Betelgeuse is a M2 I
Radius
• Smallest stars on the main sequence fall on the
bottom right
• Largest stars on main sequence fall on the top left
• At the same size, hotter stars are more luminous
than cooler ones
• At the same temperature, larger stars are more
luminous than smaller ones
Main Sequence Stars
• Fuse Hydrogen into Helium for energy
• On main sequence, mass tends to decrease with
decreasing temperature
What does this tell us
• The star’s mass is directionally proportional to
how luminous it is
• More massive, the star must have a higher nuclear
burning rate to maintain gravitational equilibrium
• So more energy is produced
Main Sequence Lifetimes
• The more massive a star on the main sequence,
the shorter its lifetime
• More massive stars do contain more hydrogen
than smaller stars
• However, the more massive stars have higher
luminosities so they are using up their fuel at a
much quicker rate than smaller stars
Ages
• Universe is thought to be about 14 billion years
old
• So less massive stars have lifetimes longer than
the age of the universe
• More massive stars have ages much younger
• So stars must be continually forming
Things to remember
• 90% of classified stars are on main sequence
• Main sequence stars are “young” stars
• If a star is leaving the main sequence, it is at the
end of its lifespan of burning hydrogen into
helium
Remember
• Largest stars on main sequence are O stars
• Largest stars that can exist are supergiants
You need to know stellar classifications
• O, B, A, F, G, K, M
• A0, A1, A2, … A9 in the order from the hottest to
the coolest
wd
white dwarfs
Classifications
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Sun is a G2 V
Betelgeuse is a M2 I
Vega is a A0 V
Sirius is a A1 V
Arcturus is a K3 III
Any Questions?