Transcript March 11

Survey of the Universe
Tom Burbine
[email protected]
Quiz #3
• Wednesday
• Covers up to last Wednesday
Atmosphere
• Atmosphere can absorb light
• Atmosphere can scatter light
• Atmosphere can distort light (twinkling)
(atmospheric scintillation)
http://www.scienzagiovane.unibo.it/English/radio-window/images/radiazioni-em.jpg
Twinkling
• Twinkling of stars is caused by moving air
currents in the atmosphere.
• The beam of light from a star passes through
many regions of moving air while on its way to an
observer’s eye or telescope.
• Each atmospheric region distorts the light slightly
for a fraction of a second.
Advantages of space-based telescopes
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It can be open 24 hours, 7 days of week
Do not have to worry about distorting effects of
atmosphere
There is no extra background of light due to
scattering of light in the Earth’s atmosphere
Observe in more wavelength regions
Figure 7.20
It does not help
• That you are closer to the stars
Great Observatories
• The Hubble Space Telescope (HST) observes visible,
infrared, and near-ultraviolet light. Launched in 1990
• The Compton Gamma Ray Observatory (CGRO) observes
gamma and x-rays. Launched in 1991. Deorbited in 2000
into the Pacific Ocean
• The Chandra X-ray Observatory (CXO) observes x-rays.
Launched in 1999
• The Spitzer Space Telescope (SST) observes in the
infrared. Launched in 2003.
Hubble (launched in 1990)
Telescope is the
size of a
school bus
2.4 m mirror
Initially
• Hubble’s primary mirror was polished to the
wrong shape
• Was too flat at the edges
• Was barely 2.3 micrometers out from the required
shape (1/50 the width of a human hair)
• Images were not focused as well as they could be
• Later shuttle mission fixed this problem by
installing a number of small mirrors
http://dayton.hq.nasa.gov/IMAGES/SMALL/GPN-2002-000064.jpg
Jupiter taken by Hubble
Compton Gamma Ray Observatory
• Launched in 1991
• Mapped the gamma rays distribution in the sky
• Dominated by emission from interactions between
cosmic rays and the interstellar gas along the plane of
our Galaxy
Chandra X-ray Observatory
• Launched in 1999
• Observed X-rays
• X-rays can be associated with gas
that is spiraling into black holes
M81
Spitzer Space Telescope
• Infrared observatory
• Launched in 2003
Andromeda Galaxy in the infrared.
Seeing dust
Sun
• Our nearest star
• Mean diameter - 1.392×106 km 109 × radius of
Earth
• Mass - 1.9891×1030 kg 333,000 × Mass of Earth
• Made out of plasma – temperatures are so high that
atoms are ionized
Figure 15.4
Temperature
Density
Parts of Sun
Core
• Core – ~15 million Kelvin – where fusion of
Hydrogen to Helium 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
Photosphere
• Photosphere is the solar surface
• Where photons escape into space
• Temperature of ~5,800 K
Chromosphere
• Thin layer of the Sun's atmosphere just above the
photosphere
• Temperatures of 4500 K to as high as 20,000 K
• Most of the Sun’s ultraviolet light is emitted from
this region
Corona
• Plasma "atmosphere" of the Sun,extending
millions of kilometers into space
• Most easily seen during a solar eclipse
• Temperature of 1 to 3 million Kelvin
Solar Wind
• Solar wind is a stream of charged particles ejected
from the upper atmosphere of the Sun
Converting 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
So E is in joules
very small amounts of mass may be converted
into a very large amount of energy and
Who came up with it?
• How much energy can be produced if you can
convert 10 kg of material completely into energy?
• E = mc2
• A) 3.0 x 108 J
• B) 3.0 x 1016 J
• C) 9.0 x 1017 J
• D) 9.0 x 1010 J
Answer
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E = 10 kg * (3 x 108 m/s) * (3 x 108 m/s)
E = 10* (9 x 1016) J
E = 90 x 1016 J
E = 9.0 x 1017 J
Mass-Energy
• E=mc2
• So Mass is a form of potential energy
• Where is one place where you see mass converted
into energy?
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
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
observe.arc.nasa.gov/nasa/exhibits/stars/star_6.html
Any Questions?