Astronomy%20101%20The%20Solar%20System%20Tuesday,[e-mail]

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Astronomy 101The Solar SystemTuesday,
ThursdayTom Burbinetomburbine_at_astro.umass.edu

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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.

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• 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 its 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/orchard
  hill/index.html.

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HWs 6, 7, 8, and 9

• Due by Feb. 23rd at 1 pm

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Exam 2

• February 25th
• Covers from last exam up to today

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Sun

• Brightest star in the sky
• Closest star to Earth
• Next Closest is Alpha Centauri, which is 4.3
  light years away

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Sun video

• http//www.space.com/common/media/video/player.php
  ?videoRefsun_storm

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Solar Constant

• Energy received at Earths distance from the Sun
• 1400 W/m2
• 50-70 reaches Earths surface
• 30 absorbed by atmosphere
• 0-20 reflected away by clouds

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http//en.wikipedia.org/wiki/FileSun_Life.png
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Absorption lines
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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

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http//www.astronomynotes.com/starsun/s3.htm
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http//www.astronomynotes.com/starsun/s3.htm
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How does Fusion Convert Mass to Energy

• What is the most famous formula in the world?

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E mc2

• 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

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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

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0.993 kg
1 kg
1 kg
0.993 kg
0.007 kg
http//observe.arc.nasa.gov/nasa/exhibits/stars/st
ar_6.html
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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
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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.

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Fusion reaction

• Much more complicated than
• 4 protons ? helium-4 2 neutrinos energy

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Deuteron Deuterium (hydrogen with a
neutron) nucleus
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Proton-Proton Chain Reaction

• This reaction occurs 1038 times each second
• It if occurred faster, Sun would run out of fuel

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Neutrinos

• 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.

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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

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What was the solar neutrino problem?

• Less neutrinos appeared to have been produced
  from the Sun than expected from models

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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

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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

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What is happening to the amount of Helium in the
Sun?

• A) Its increasing
• B) its decreasing
• C) Its staying the same

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What is happening to the amount of Helium in the
Sun?

• A) Its increasing
• B) its decreasing
• C) Its staying the same

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So how does the Sun stay relatively constant in
Luminosity (power output)
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http//www-ssg.sr.unh.edu/406/Review/rev8.html
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Figure 15.8
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Figure 15.4
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Density
Temperature
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Parts of SunCore

• Core 15 million Kelvin where fusion occurs

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Figure 15.4
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Radiation zone

• Radiation zone region where energy is
  transported primarily by radiative diffusion
• Radiative diffusion is the slow, outward
  migration of photons

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Figure 15.13
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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

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Figure 15.4
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Convection Zone

• 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

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Figure 15.14
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Granulation bubbling pattern due to
convection bright hot gas, dark cool gas
Figure 15.14
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Figure 15.10
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Figure 15.4
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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

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Stars have different colors
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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

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1913
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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

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Flemings classification

• A - strongest hydrogen emission lines
• B - slighter weaker emission lines
• C, D, E, L, M, N
• O - weakest hydrogen lines emission lines

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Annie Jump Cannon (1863-1941)

• Cannon reordered the classification sequence by
  temperature and tossed out most of the classes
• She devised OBAFGKM

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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

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OBAFGKM

• Oh Be A Fine Girl/Gal Kiss Me
• http//www.mtholyoke.edu/courses/tburbine/ASTR223/
  OBAFGKM.mp3

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http//physics.uoregon.edu/jimbrau/BrauImNew/Chap
04/FG04_05.jpg
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http//spiff.rit.edu/classes/phys301/lectures/spec
_lines/spec_lines.html
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http//scope.pari.edu/images/stellarspectrum.jpg
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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.

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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

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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

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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.
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Hertzsprung-Russell Diagram

• Both plotted spectral type (temperature) versus
  stellar luminosity
• Saw trends in the plots
• Did not plot randomly

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Remember

• Temperature on x-axis (vertical) does from higher
  to lower temperature
• O hottest
• M - coldest

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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

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wd white dwarfs
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• 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

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Classifications

• Sun is a G2 V
• Betelgeuse is a M2 I

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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

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Main Sequence Stars

• Fuse Hydrogen into Helium for energy
• On main sequence, mass tends to decrease with
  decreasing temperature

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What does this tell us

• The stars 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

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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

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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

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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

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Remember

• Largest stars on main sequence are O stars
• Largest stars that can exist are supergiants

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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

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wd white dwarfs
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Classifications

• 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

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Any Questions?