Download Key Topics Astronomy Unit

Astronomy Unit
Key Topics
History of the Universe
Big Bang Theory: most widely accepted
theory for the origin of our universe.
• States that 12-14 billion years ago, the universe was only a
few millimeters across.
• According to this theory, the contents of the universe
expanded explosively into existence about 13.7 billion
years ago.
• After the big bang, the universe expanded quickly, and
continues to expand, and cooled enough for atoms to
form.
• Gravity pulled the atoms together into gas clouds that
eventually became stars, which comprise young galaxies.
Evidence of Big Bang Theory
1. Galaxies appear to be moving away from us at speeds
proportional to their distance.
• This is called Hubble’s Law, named after Edwin Hubble who
discovered this phenomenon in 1929. This supports the
expansion of the universe and suggests that it was once
compacted.
2. If the universe was initially very hot as the big bang
suggests, there should be remnants of this radiation.
• In 1965, Radioastronomers Arno Penzias and Robert Wilson
discovered Cosmic Background Radiation, which supports
the Big Bang.
3. The abundance of “light elements” Hydrogen and Helium
found in the universe is thought to support the Big Bang.
Technology and the Universe
Technology provides the basis for many new discoveries
related to space and the universe.
• Visual, radio, and x-ray telescopes collect info from
across the entire electromagnetic spectrum.
• Computers are used to manage data and complicated
computations.
• Space probes send back data and materials from
remote parts of the solar system.
• Accelerators provide subatomic particle energies that
simulate conditions in the stars and in the early history
of the universe before stars formed.
What is a Galaxy?
A galaxy is a group of billions of individual
stars, star systems, star clusters, dust and
gas bound together by gravity. There are
billions of galaxies in the universe, and they
are classified by size and shape. They vary
in size from a few thousand to a hundred
thousand light years across.
A spiral galaxy
3 Types of Galaxies
1.Elliptical Galaxies: round or oval in
shape; some of the largest galaxies are
elliptical galaxies. They are thought to be
the most common type of galaxy in the
nearby universe.
Elliptical
Galaxy M87
3 Types of Galaxies (continued)
2.Spiral Galaxies: disc shaped galaxy that
has a bulge in the middle; have spiral
arms; makes up more than 50% of
galaxies
Spiral Arm: contains gas
and dust clouds and
mainly hot, young stars
Central bulge is packed
with old red and yellow
stars, which glow the
brightest
3 Types of Galaxies (continued)
3.Irregular Galaxies: cannot be classified
as elliptical or spiral; makes up about 3%
of galaxies.
Irregular Galaxy
Our Galaxy; The Milky Way
• Our solar system is part of the Milky Way Galaxy,
which is a spiral galaxy.
• It has more than 100 billion stars and a diameter of
more than 100,000 light years.
• At the center is a bulge of stars from which are
spiral arms of gas, dust, and most young stars.
Hubble’s Law
• Hubble’s Law states that galaxies which are
farther away have a greater red shift, so the
speed at which a galaxy is moving away is
proportional to its distance from the Earth.
Hubble’s Law and the Red Shift
• The red shift is a phenomenon due to Doppler
shifting, so the shift of light from a galaxy to the
red end of the spectrum indicates that the
galaxy is moving farther away.
• This is evidence for the Big Bang Theory
because it tells us that the universe is still
expanding.
• http://wosu.pbslearningmedia.org/resource/phy
03.sci.phys.fund.hubble2/hubbles-expandinguniverse/
Stars
• Early in the formation of the universe, stars
coalesced out of clouds of hydrogen and
helium and clumped together by gravitational
attraction into galaxies.
Stars
• When heated to a sufficiently high
temperature by gravitational attraction, stars
begin nuclear fusion, which converts matter to
energy and fuse lighter elements into heavier
ones.
• All of the elements, except for hydrogen and
helium, originated from the nuclear fusion
reactions of stars.
Classification of Stars
• Stars are classified by:
•
Color : from hottest to coldest:
• O (blue), B (blue), A (blue), F (blue to white), G
(white to yellow), K (orange to red), M (red)
• Size
• Luminosity: amount of energy released from the
star; measured in Watts
• Mass
Stars
• A star’s mass determines the star’s place on
the main sequence and how long it will stay
there.
• Patterns of stellar evolution are based on the
mass of the star.
• Stars begin to collapse as the core energy
dissipates.
• Nuclear reactions outside the core cause
expansion of the star, eventually leading to the
collapse of the star.
Hertzsprung-Russell Diagram
• A Hertzprung-Russell diagram is used to
estimate the sizes of stars and predict
how stars will evolve.
• Most stars fall on the main sequence of
the H-R diagram, a diagonal band
running from the bright hot stars on the
upper left to the dim cool stars on the
lower right.
Hertzprung-Russell Diagram