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Distribution of Matter in Space
What is a Star?
• Much of the visible matter in space makes
up stars -- hot, glowing spheres of hydrogen
gas that give off tremendous light energy.
• The billions and billions of stars vary in:
– Size
– Density
– Temperature (colour depends on surface
temp; very hot = blue; cooler = red)
– Brightness (luminosity)
• H-R
animation
• Star
Spectra
(Gizmo)
What is the life cycle of star?
http://www.google.ca/imgres?q=star+life+cycle&hl=en&biw=1152&bih=683&tbm=isch&tbnid=iV0L5uG5BJhmmM:&imgrefurl=http://www.seasky.org/celestialobjects/stars.html&docid=O-VRp6eOvD9w8M&imgurl=http://www.seasky.org/celestialobjects/assets/images/starlife.jpg&w=560&h=287&ei=jsBlUa_zFMGFiALn6IGwDQ&zoom=1&iact=hc&vpx=464&vpy=60&dur=1650&hovh=161&hovw=314&tx=213&ty=1
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The Birth of a Star
• Just like organisms live, grow and die, so do stars.
• Gravity pulls gas and dust in a NEBULA together into a
rotating sphere (composed of ~75% H and 23% He)
• As more material is drawn into the spinning ball, the mass at
its core increases causing the temperature to rise and
possibly start to glow (called a pro-star)
• As the process continues, heating in the core can reach
10 000 000oC and causes the fusion of hydrogen into
helium.
• As a star is ‘BORN’, huge amounts of radiation are given off!
• A star will emit radiation for millions or billions of years!
Life and Death of Stars
• Depending on the mass of a star it can be either a:
Sun-like star
or
Massive star
• They will spend most of their lives (millions to billions of
years) in a stable state converting hydrogen to helium
• But just like fuel in a car runs out, so will the hydrogen
• So what happens when the hydrogen is used up????
When the fuel runs out?
• When the hydrogen runs out, the stable star shrinks
heating the helium core so it starts fusing to carbon,
then to other elements.
• As gravity causes the star to contract, further nuclear
reactions occur, leading to the expansion of the outer
layers
• Sun-like star  RED GIANT
– Our sun will do this in 5 billion years
– It’s diameter will extend past the orbit of Mars
• Massive star  RED SUPERGIANT
Red Giant vs. Red Supergiant
• Red Giant
• Red Supergiant
The Final Stage of a Star’s Life
For a Sun-like star:
For a Massive star:
• Fusion ends when the temp.
is not hot enough to keep the
reaction going
• With no heat, the pressure
decreases and gravity causes
the star to slowly collapse on
itself
 WHITE
DWARF
• Eventually it will fade into a
cold, dark, BLACK DWARF (it
takes so long none have
formed in the universe yet)
• Fusion ends when the fuel
runs out
• With no heat input, gravity
wins and the star collapses
quickly and sends out a
shock wave
• This causes the outer part of
the star to explode in a
SUPERNOVA
• If the star is not destroyed it
will become a NEUTRON
STAR or BLACK HOLE
After a supernova….
• NEUTRON STAR
• BLACK HOLE
• Is a rapidly spinning
object only about 30km
in diameter
• Highly dense remnant of a
star in which gravity is so
strong that not even light
from the radiation going
on inside the remnant can
escape
• Scientists only know
about them because of
hoe material near them
become very hot and
bright
What can colour and
temperature tell us about
the life cycle of star?
Hertzsprung-Russel Diagram
• These two scientists began comparing the surface
temp. of stars with its brightness.
• The noticed a pattern (pg. 385 Fig: 1.18):
– 90% of all stars fit into their main sequence;
– Our sun fits in the middle of the sequence
– White dwarfs and super giants are the exception
• This pattern accounts for our current theory that
stars evolve and change over long periods of time
What are Galaxies?
http://apod.nasa.gov/apod/ap020901.html
Galaxies
• A galaxy is a grouping of millions or billions of stars,
gas and dust, held together by gravity
• Elliptical: a disk or football shaped galaxy made up of
mostly old stars
• Spiral: Milky Way style galaxies with long curved arms
leading away from a bright central core
• Irregular: Small galaxy that lacks a definite shape
How do organize the night sky?
• Constellations – groupings of stars we see
as patterns in the night sky
– There are 88 recognized by the International
Astronomical Union (i.e. Ursa Major)
• Asterisms – unofficially recognized star
groupings
– Big Dipper – see pg. 390 Fig. 1.23
Star Groups
• Star clusters like Pleiades – SEVEN sisters is an
asterism with an ancient myth!
• Cassiopeia was a queen of Ethiopia known for her
beauty. She was more beautiful than the Sea
nymphs she believed. This enraged Poseidon. To
punish Cassiopeia he sent Cetus the whale to
destroy the coast of the Queen’s homeland!
• The Nymphs sought eternal punishment, arranging
for her to be placed in the heavens tied to a chair!
Describing the Position of Objects in Space
• Our reference point for measuring the position of two objects in
space is usually the Earth.
• Altitude and Azimuth are calculated from the observers position.
• Altitude is from 0° at the horizon to 90° straight up.
• ZENITH refers to the highest point directly overhead
• Azimuth determines the direction
•
(0°= north, 90°= east, 180°= south, 270°= west)