The Universe PHYSICAL SCIENCE Our Place in the Universe Scale of the Universe
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- The Universe PHYSICAL SCIENCE Our Place in the Universe Scale
of the Universe
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- Exploring the Universe Star a large glowing ball of gas in
space Generates energy through nuclear fusion in its core The Sun
is the closest star to use, and is of fairly average size Formed by
gravity Why do stars have to be massive in order to be a star?
Distances to the Stars Space distances are so huge normal units
arent very useful Light-year (LY) - The distance that light travels
through a vacuum in one year Astronomical Unit (AU) 1 AU = Distance
from Sun to Earth = 93 million miles How do we measure the distance
to the stars?
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- How to measure distance to a star Parallax Triangulation
Parallax Triangulation Only works on stars within 400 ly Look at a
star when Earth is in two diff positions and see how its position
relative to the stars behind it change Scientists have developed
other ways to estimate distances to further stars
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- Properties of Stars Astronomers classify stars by their color,
size, and brightness Color Indicates stars temperature Red Coolest
Blue- Hottest
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- Star Color Color and Temperature A stars color indicates the
temperature of its surface. The hottest stars, with surface
temperatures above 30,000 K, appear blue. The surfaces
(photospheres) of relatively cool red stars are still a toasty 3000
K or so. Stars with surface temperatures between 5000 and 6000 K
appear yellow, like the sun.
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- Spectral Classes of Stars
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- Star Brightness Apparent Brightness How bright it looks from
Earth Absolute Brightness How bright it actually is Its like
measuring the brightness of all the stars when they are all equally
far from you Size and temperature Light becomes fainter with
distance
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- Size & Mass Once astronomers know a stars temperature and
absolute brightness, they can estimate its diameter and then
calculate volume Scale of the Stars Scale of the Stars Scale of the
Universe Scale of the Universe
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- Hertzprung- Russel Diagram Used to estimate sizes of stars and
their distances, and to infer how stars change over time 90% of all
stars found on main sequence Relates brightness, Temp, Size, &
Color
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- Composition of Stars Absorption Lines Scientists determine the
chemical makeup of stars by looking at Absorption lines
Spectrograph instrument that spreads light from a hot glowing
object into a spectrum Different elements absorb different
wavelengths of light. Thus removing them from the spectrum. The
blank spaces (absorption lines) in the spectrum below represent
different elements in that star Each star has its own unique
spectrum. Most Stars have a chemical makeup that is similar to the
Sun, with H and He together making up 96 to 99.9% of the stars
mass
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- Why are Stars Round? Gravity tries to get everything as close
to the center as possible. The only way to achieve this is if it is
in a spherical shape Stars are held in balance by Two Forces
Gravity - Pulls star inwards Thermal Pressure from Nuclear Fusion
Pushes star outward The relative strength of these determine the
stars size. These two forces are balanced before a star dies
Nuclear Fusion Two atoms are pushed together so hard they fuse into
one and create a different element
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- Life Cycle of stars
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- Death of a Star Low & Medium Mass Stars Planetary Nebula
White Dwarf High Mass Stars Supernova Neutron Star Black Hole
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- When a star dies. White Dwarf (C.P. Powerpoint) Neutron Stars
Black Holes
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- Groups of Stars Galaxy Huge group of individual stars, star
systems, star clusters, and gas bound together by gravity Our
Galaxy Milky Way Each consists of Billions of stars. Sometimes
Trillions Four types Spiral, Barred-Spiral, Elliptical,
Irregular
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- Location of solar system Central bulge Nucleus Overhead View of
Our Galaxy Disk of spiral arms containing mainly young stars
Central bulge containing mainly older stars Nucleus Halo containing
oldest stars Side View of Our Galaxy
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- Big Bang Theory Explanation The universe came into existence in
a single moment, an event called the Big Bang The event happened
13.7 Billion years ago All matter and energy were concentrated into
a single infinitely small point Timeline of the universe Timeline
of the universe Video Video Big bang occurred 13.7 billion years
ago. First stars and galaxies formed 200 million years after big
bang. Solar system formed 4.6 billion years ago. Earth today
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- Evidence for Big Bang Edwin Hubble -Red Shift of Galaxies Light
from most galaxies undergoes a redshift. Light is experiencing
Doppler effect and shifting to longer wavelengths (red light). This
means it is moving away from us. This is noticed in most galaxies.
Shows universe is expanding By looking at the rate its expanding we
can calculate how long its been expanding, thus inferring the age
of the universe More distant galaxies are moving away from Earth
faster than closer galaxies Cosmic Microwave Background Radiation
Video Evidence for Big Bang CMB Video Evidence for Big Bang Video
Red Shift of Galaxies Video Red Shift of Galaxies Rubber band
activity Pg. 855 Doppler Effect with Light Waves Stationary Moving
towards Moving away
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- Continued Expansion All galaxies are expanding away from all
other galaxies Further way the galaxy the greater the expansion
Will Universe continue expanding forever?? Recent evidence shows
that the rate of expansion is actually increasing
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- Cosmic Microwave Background Radiation Faint distant glow
detected in every direction Energy produced during the big bang
still travelling through the universe
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- Matter in the Universe Dark matter Matter that does not give
off light Cannot see it but we know its there because of its
gravitational effects