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Tahsiri: Lecture notes :
Kenealy: Read chapters (1-6).
Please click on the Virtual library www reference guides after the red arrow for further Discussions and Illustrations on the important terms relevant to my lectures.
* Our galaxy is a huge, rotating disk-shaped group of stars that we see in the sky as the Milky Way from our location about two-thirds of the way out from the center. Most of the stars of the galaxy are found in two spiral arms that extend outward from the center. Spiral galaxies are other collections of stars that resemble our galaxy. The universe apparently consists of widely separated galaxies of stars.
a) Illustrations
(1) The
Milky Way Galaxy (2) The Milky
Way (3) Galaxies (4) Exploring
our Galaxy (5) The
Hot Big Bang (6) A
brief introduction to Universe (7)
The
nature of the Universe (8) The
Big Bang model of the Universe.
(9) The
hot Big Bang model (10) The
Big Bang (11) God,
Genesis and the Big Bang (12) Closed
and Open Model of the Universe (13)
The
Big Bang
* Tracing the observed motions
of galaxies back in time implies that, about 15 billion years
ago, the universe consisted of a single point that expanded rapidly
in the Big Bang. Space itself was compressed to a point at that
instant-the Big Bang happened everywhere at once. The cosmological
redshift occurs as a
photon's wavelength is "stretched" by cosmic expansion.
The extent of the observed redshift is a direct measure of the
expansion of the universe since the photon was emitted. The spectral
lines of distant galaxies show a doppler shift to the red arising
from motion away from the earth. Since the speed of recession
is observed to be proportional to distance, the red shift means
that all the galaxies in the universe are moving away from one
another. This expansion of the universe began about 15 billion
years ago.
* The big bang theory holds that the universe originated in a great explosion about 15 billion years ago. Radiation left over from the big bang and doppler-shifted to radio frequencies has been detected. If the explosion was violent enough, the expansion of the universe will continue forever; if not, the universe will eventually begin to contract and will end up in a big crunch after which another cycle of expansion and contraction may occur. It is likely that the solar system originated as part of an evolutionary process, and that planetary systems are quite common elsewhere in the universe.
b) Illustrations(1) Expansion
of the Universe (2) Doppler
shift (3) The
Expansion of the Universe (4) Hubble
Expansion of the Universe (5) The
Expanding Universe (6) Doppler
shift (7) Hubble's
Law and the Expansion of the Universe
(8) Expansion
of the Universe (9) Hubble's
law and the Expanding Universe (10)
Expansion
of Universe simulation (11) Cosmology
Tutorial (12) Expansion
of Universe (13) Hubble's
Law
* The cosmic microwave background
is isotropic blackbody radiation that fills the entire universe.
Its present temperature is about 3 K. Its existence is evidence
that the universe expanded from a hot, dense state. As the universe
has expanded, the initially high-energy radiation has been redshifted
to lower and
lower temperatures.
c) Illustrations(1) The
Cosmic Microwave Background Radiation
(2) Frequently
Asked Questions (3) Cosmic
expansion
* Radio waves from space
are produced by extremely hot gases, by fast electrons that move
in magnetic fields and by atoms and molecules excited to radiate.
Especially notable sources are quasars, distant objects that emit
both light and radio waves strongly and that may be powered by
supermassive black holes at their centers.
d) Illustrations(1) Radio
Waves (2) What
are radio waves? (3) Frequently
Asked Questions About Quasars (4)
Quasars (5) Quasars (6) Black
Hole (7) Quasi
Stellar Objects
* Cosmic rays are atomic
nuclei, mostly protons, that travel through the galaxy at speed
close to that of light. They probably were ejected during supernova
explosions and are trapped in the galaxy by magnetic fields.
e) Illustrations(1)
Cosmic Rays (2) Cosmic
Rays (3) Cosmic
Rays: What Are They? (4) Supernova
Explosions (5) The
Supernova Explosions
*
Cosmological principle: In cosmology-the study of the universe as a whole
assume that the universe is homogeneous and isotropic on large
scales.
f) Illustrations(1) Cosmological
Principles (2) Cosmological
Principle
* Olbers's paradox:
If the universe were homogeneous, isotropic,
infinite, and unchanging, then the night sky would be bright
because any line of sight would eventually intercept a star. The
fact that the night sky is instead dark is called Olbers's paradox. Its resolution is that we see
only a finite part of the universe-the region within about 15
billion light-years, beyond which light has not yet had time to
reach us.
g) Illustrations(1) Olbers'
Paradox and the Dark Night Sky (2)
The
darkness of the night sky (3) Olbers' Paradox
* The large-scale structure
observed in the universe today formed when density inhomogeneities
in the dark
matter clumped and grew to create the "skeleton" of
the structure now observed. Normal matter then
flowed into the densest regions of space, eventually forming the
galaxies we now see. "Ripples" in the
microwave background are the imprint of these early inhomogeneities
on the radiation field.
h) Illustrations(1) Dark
Matter (2) Dark
Matter
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