Transcript Chapter 2 - The Solar System

Chapter 2
The Solar System
Solar System
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Comprised of
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Sun
Inner Terrestrial Planets (Mercury, Venus, Earth,
Mars)
Main Asteroid Belt
Outer Gas Giants or Jovian planets (Jupiter, Saturn,
Uranus, Neptune)
Pluto and the Kuiper Belt
Oort Cloud
Electromagnetic Radiation (Light)
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Visible light, radio waves, infrared light,
microwaves are all examples of
electromagnetic radiation.
The type of electromagnetic radiation
depends on the frequency. Visible light is
the portion of the electromagnetic
spectrum, between the frequencies of
7.5×1014 Hz and 3.8×1014 Hz.
Electromagnetic Radiation (Light)
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The higher the frequency, the higher the energy
of the electromagnetic radiation. Conversely, the
longer the wavelength, the lower the energy of
light (See Diagram).
Gamma rays and x-rays are very dangerous
because of their high frequency and energy. The
Earth’s electromagnetic field and atmosphere
block radiation at those high frequencies thus
protecting us from them.
Any frequencies of light that the Earth blocks
must be studied from space.
Electromagnetic Radiation (Light)
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Light simultaneously exhibits properties of
both waves and particles. The particle is
called a photon.
The speed of light (denoted classically as
c) in a vacuum is exactly equal to
300,000,000 meters per second
(186,000 miles per second).
The Sun
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The Sun is a star. It is one of more than 100
billion stars in our galaxy.
It contains more than 99.8% of the total mass of
the Solar System.
By mass, the Sun is, at present, about 70%
hydrogen and 28% helium everything else
("metals") amounts to less than 2%. This
changes slowly over time as the Sun converts
hydrogen to helium in its core.
The Sun
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All matter in the Sun is in the form of plasma due
to its extreme temperature.
The surface of the Sun, called the photosphere,
is at a temperature of about 5800 Kelvin (10,000
degrees F).
The corona, extends millions of miles into space
but is visible only during a total solar eclipse.
Temperatures in the corona are over 1,000,000
Kelvin.
The Sun
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The Sun's energy output of 386 billion billion
megawatts is produced by nuclear fusion
reactions. (By comparison Hoover Dam
produces 2,000 megawatts.) Each second about
700,000,000 tons of hydrogen are converted to
about 695,000,000 tons of helium and energy in
the form of gamma rays. As it travels out toward
the surface, the energy is continuously absorbed
and re-emitted at lower and lower temperatures
so that by the time it reaches the surface, it is
primarily visible light.
The Solar Wind
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In addition to heat and light, the Sun also emits
a stream of charged particles (mostly electrons
and protons) known as the solar wind which
travels throughout the solar system at about 450
km/sec. The exact composition of the solar wind
has not yet been measured. A sample return
mission, Genesis, returned to Earth in 2004 and
is undergoing analysis, but it was damaged by
crash-landing when its parachute failed to
deploy on re-entry to Earth's atmosphere.
The Active Sun
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Since it’s not a solid, the outer layers of the Sun
exhibit different rates of rotation. At the equator
the surface rotates once every 25.4 days; near
the poles it's as much as 36 days. This
differential rotation causes its magnetic field
lines to become twisted together over time,
causing magnetic field loops to erupt from the
Sun's surface and trigger the formation of the
Sun's dramatic sunspots and solar prominences.
The Active Sun
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Sunspots are "cool" regions (they look
dark only by comparison with the
surrounding regions). Sunspots can be
very large, as much as 50,000 km in
diameter. The frequency of sunspots
varies cyclically over a 22 year period with
the magnetic poles switching every 11
years.
The Active Sun
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Many solar prominences (closeup) break
apart emitting a burst of plasma (protons
and electrons). This is called a coronal
mass ejection (CME). These expand
away from the sun at supersonic speeds
carrying up to 50 million tons of material.
The Active Sun
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A solar flare is a violent explosion in the Sun's
atmosphere with an energy equivalent to tens of
millions of hydrogen bombs. The frequency of
solar flares varies, from several per day when
the Sun is particularly "active" to less than one
each week when the Sun is "quiet". Solar flares
may take several hours or even days to build up,
but the actual flare takes only a matter of
minutes to release its energy.
The Active Sun
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CMEs, along with solar flares, can cause particularly
strong polar auroras (northern and southern lights), can
disrupt radio transmissions, cause power outages
(blackouts) and damage satellites and electrical
transmission lines. The radiation from the flares can give
passengers in airplanes a dose of radiation equivalent to
a medical X-ray
The radiation risk posed by solar flares and CMEs is one
of the major concerns in discussions of manned missions
to Mars. Some kind of physical or magnetic shielding will
be required to protect the astronauts.
The Sun’s Future
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The Sun is about 4.5 billion years old.
Since its birth it has used up about half of
the hydrogen in its core. It will continue to
radiate "peacefully" for another 5 billion
years or so (although its luminosity will
approximately double in that time). It will
then enter its red giant phase, expanding
as the hydrogen fuel in the core is
consumed and it starts to burn helium.
The Sun’s Future
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Following this phase, giant thermal
pulsations will cause the Sun to throw off
its outer layers to form a planetary nebula.
The Sun will subsequently become a white
dwarf, slowly cooling over many more
billions of years. Although commonplace
by stellar standards, these events will
likely result in the total destruction of the
Earth.