Stars
What you need to learn
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What the structure and processes of the Sun are
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What properties are used to observe and measure
stars
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How stars change during their lives and what is
left when they die
The Sun
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Largest object in our solar system
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Equal to 109 Earths or 10 Jupiters
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330,000 more massive than Earth
¡ Contains 99% of all the mass of the solar system
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The liquid core is probably 13 times more dense
than lead
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Very hot core = 1 x 107 K
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Consists of plasma (most common state of matter)
Layers of the Sun
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Visible surface is called the photosphere
(average temp. = 5800K)
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Chromosphere is the 2nd layer which
appears red when seen
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Top layer is called the corona which is only
visible with special instruments
Solar Wind
¡ Gases that flow outward from the corona at high speeds
l They are charged particles traveling at a fast rate
l When they collect in space you see an aurora
Solar Activity
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Sunspots: dark
spots on the surface of the photosphere
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They are actually
very bright but cooler than surrounding areas
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Occur in pairs
because of their magnetic polarity and can last a couple of months
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Cycle in number
every 11.2 years, but when the Sun’s poles reverse it takes 22.4 years
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Coronal holes:
located over sunspot groups; low density regions
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Solar Flares:
violent eruptions of particles
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Prominence: arc
of gas that is ejected from the photosphere
Solar Interior
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Fusion (combining
of lightweight nuclei) occur within the sun
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Fission
(splitting of heavy atomic nuclei)
During this process matter is actually being
lost (Einstein’s theory of special relativity) and being converted to energy
which powers the Sun
Structure of an Evolved Star
Energy from the Sun
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The sun has burned up about half of its energy
(about 5 billion years left)
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Above the Earth’s atmosphere absorb about 1354 W
of energy per 1 m2 (13 100 watt lightbulbs could be powered from 1 m2)
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Energy travels through space in the form of
electromagnetic radiation
Measuring Stars
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Groups of stars
are called constellations
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88 were named by
the ancient Greeks
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Groups of stars
are actually very far away from each other
¡ When 2 stars are gravitationally bound together and
orbit a common center of mass they are called binary stars (most look like just
one star)
Measuring Stars cont.
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Star distances are measured in light years or
larger units called parsec
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Parallax (apparent shift in position caused by
the motion of the observer) helps scientists measure distances
Basic Properties of Stars
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Magnitude: how bright it appears
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Stars can be compared by ranking them on a scale
developed by the ancient Greeks
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Apparent Magnitude: how bright it appears to be
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Uses a modified system
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Absolute Magnitude: the brightness an object
would have if it were placed at a distance of 10 pc
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Accounts for the distance
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Luminosity: Measure of energy output from the
surface of a star per second
Spectra of Stars
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Classification of spectral types based on
temperature
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Wavelength shifts: determine if stars are
approaching or going away
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Moving closer: shift toward shorter wavelengths
(blue shifted)
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Moving away: longer wavelengths (red shifted)
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Hertzsprung-Russell diagram: looks at mass,
luminosity, temperature, and diameter of stars
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Broad strip of the spectrum is called the main
sequence
Stellar Evolution
¡ Mass governs a star’s temperature, luminosity, and
diameter
l The more massive it is the hotter and more dense it is
l The hotter it is determines the brightness
¡ Gravity and pressure balance each other in a star
Stellar Evolution
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If the temperature
in the core of a star becomes high enough, elements heavier than hydrogen but
lighter than iron can fuse together
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Stars such as the
Sun end up as white dwarfs
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Stars up to about
8 times the Sun’s mass also from white dwarfs
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Stars with masses
between 8-20 times the Sun’s mass end up as neutron stars
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More massive
stars end up as black holes
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A supernova
occurs when the outer layers of the star bounce off the neutron star core, and
explode outward