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ASTRO 209 (Introduction to Astronomy II) THE COSMOS CHAPTER NOTES COMPLETE UNIVERSITY OF CALGARY
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ASTRO 209 (Introduction to Astronomy II) THE COSMOS CHAPTER NOTES COMPLETE UNIVERSITY OF CALGARY
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ASTRO 209 (Introduction toAstronomy II) THE COSMOS
CHAPTER NOTES COMPLETE
UNIVERSITY OF CALGARY
, lOMoAR cPSD| 19857451
Chapter 5:
(first half of chapter 5 is written by hand in notebook - make sure to review)
Start pg 145:
• Atoms come in different types, and each type corresponds to a different chemical element.
• Chemists have identified more than 100 chemical elements and fire, water, air, and earth are
not among them
• Most familiar: helium, hydrogen, carbon, oxygen, silicon, iron , gold, silver, lead, and
uranium.
• ATOM STRUCTURE:
o Atoms are made of particles that we call protons, neutrons, and electrons.
o Protons are found in the tiny nucleus at the center of the atom. - the rest of the atoms
volume contain the electrons that surround the nucleus.
o Properties of an atom depend mainly on the electrical charge in its nucleus. (proton +1,
electron -1, neutron have no charge) oppositely charges particles attract, and vice
versa.
• ATOMIC TERMINOLGY:
o (review from past science) --> each chemical element contains a different number of
protons in its nucleus = atomic number. The combined number of protons and
neutrons is the atomic mass number.
o Versions of an element with different numbers of neutrons are called isotopes of that
element .
o MOLECULES
• Atoms can combine to from molecules. Some molecules consist of 2 or more
atoms of the same element. (EX: H20)
• PHASES OF MATTER
o Interaction between light and matter depend on the physical state of the matter, which
is called the matter's phase.
o Example --> water (h20) can exist I three phases: solid, liquid, gas or (vapor).
o A chemical bond is the interactions between electrons that hold the molecule together.
o Phase changes occur when one type of bond is broken and replaced by another. Changes
in temperature or pressure, (or both) can cause phase changes.
o Temp --> as a substance is heated, the avg Kinetic Energy of Its particles increase, which
causes the particles to break the bonds they have with their neighbors.
o HOW CAN OUR ATMOSPHERE CONTAIN WATER IN THE GAS PHASE (CLOUDS/RAIN)??:
o The process in which particles break free of their bonds is called vaporization (solid -
liquid, solid - vapor, liquid - vapor)
o Vaporization from a solid is called sublimation, and vaporization from a liquid is called
evaporation.
o Molecular Dissociation is when molecules split into pieces
o Charged atoms whether positive or negative are called ions. ¨And the process of
stripping electrons from atoms is called ionization.
, lOMoAR cPSD| 19857451
o In a hot gas, where atoms have been ionized is called a plasma
o Temperature is the primary factor determining the phase of a substance and the ways in
which light interact with it (but pressure also plays a role)
o Pressure is the force per unit area pushing on an objects surface.
• HOW IS ENERGY STORES IN ATOMS:
o To produce light, objects must somehow transfer energy contained in their matter into
vibrations of electric and magnetic fields that we call light.
o Only particles with a charge can interact with light
o Atoms contain energy in 3 different ways:
• Virtue of their mass (possess mass energy in the amount mc^2)
• Possess kinetic energy by virtue of motion
• Contain electrical potential energy that depends on the arrangement of
their electrons around the nuclei.
o Energy levels in Atoms:
o the energy stored by electrons in atoms has a strange but important property: the
electrons can only have particular amounts of energy, and not other energies in-
between.
o The possible energies of electrons are known as the energy levels of an atom.
o Energy level transitions: an electron can move up, or down a level of energy, (only when
it gains or loses the specific amount of energy separating two levels)
o Level 1 = 0ev, Level 2 = 10.2ev Level 3 = 12.1ev Level 4 = 12.8ev Level 5
(IONIZATION LEVEL) = 13.6ev (this is where electron can escape the atom)
o If the electron gains enough energy to reach the ionization level, it escapes the atom
completely = ionizing the atom --> excess energy is transferred to kinetic energy of the
free-moving electron.
▪ LEARNING FROM LIGHT:
o The process of obtaining a spectrum and reading the information it contains is calls
spectroscopy.
▪ 3 TYPES OF SPECTRA
▪ Spectrum of a lightbulb, is a rainbow of color, and because it spans a broad
range of the WL's without interruption = CONTINOUS SPECTRUM
▪ A thin or low density cloud of gas emits light only at specific WL's that depend
on temperature and composition-spectrum contains bright emission lines and
therefore is called the EMISSION LINE SPECTRUM
▪ If a cloud of gas lies between us and a light bulb, we till see most of the
continuous spectrum, but the cloud absorbs light of specific WL's so the spectrum
shows dark absorption lines over the background rainbow = ABSORPTION LINE
SPECTRUM
o (NOTE: SPECTRA ON GRAPHS, ABSORPTION LINES APPEAR AS DIPS ON THE
BACKGROUND OF RELATIVELY HIGH INTENSITY LIGHT WHILE EMISSION LINES LOOK
LIKE SPIKES ON THE BACKGORUND WITH LITTLE OR NO INTENSITY.
o The many dark absorption lines over a background rainbow of color tell us that we are
essentially looking at a hot light source through a cooler gas (cloud).
• EMISSION LINE SPECTRA:
, lOMoAR cPSD| 19857451
o In a gas -electrons move faster obviously, but when they hit into one another could
possibly create enough energy to move it up a level
o Electrons cant stay in higher energy levels for long. They always fall back to level one in a
tiny fraction of a second. (the energy that the electron loses goes into emitting a
photon of light. --> specific wl's and energy
• ABSORPTION LINE SPECTRA:
o Hydrogen atoms can absorb photons from a light bulb if it creates enough energy to
transfer to the next level.
o The fact that hydrogen emits and absorbs light at specific at specific wl's makes it
possible to detect its presence in distant objects.
• REFLECTED LIGHT SPECTRA:
o Planets and moons reflect some light that falls on them.
o Objects that are colored absorb all colors of light except the color they are (red shirt
absorbs blue light and reflects red)
o Thermal Radiation:
o Thermal radiation (sometimes known as blackbody radiation) - Thermal radiation is
electromagnetic radiation emitted from a material that is due to the heat of the
material, the characteristics of which depend on its temperature its spectrum is called
thermal radiation spectrum
o These Spectra show the intensity of light per unit surface area, not the total amount of
light emitted by an object.
• TWO LAWS OF THERMAL RADIATION:
o (Stefan boltzmann law): Each square meter of a hotter object's surface emits more light
at all wavelengths.
o ( Wien's Law): Hotter objects emit photons with a higher average energy --> which
means a shorter average WL. That is why the peaks of the spectra are at shorter WL's
for hotter objects.
o (fireplace poker example from class)
• HOW DOES LIGHT TELL US THE SPEED OF A DISTANT OBJECT?:
o From light, we can learn about the motion of distant objects from changes in their
spectra caused by the Doppler Effect.
o Doppler Effect: an increase (or decrease) in the frequency of sound, light, or other
waves as the source and observer move toward (or away from) each other. The effect
causes the sudden change in pitch noticeable in a passing siren, as well as the redshift
seen by astronomers.
o The doppler effect causes similar shifts in the WL's of light.
o Because shorter WL's of visible light are bluer, the Doppler shift of an object toward us is
called a blueshift.
o If an object is moving away from us, causing light to shift to longer WL's this is called a
redshift. Because longer WL's are redder
o Rest Wavelengths: stationary wavelengths
o Components of motion:
• Important to note that a doppler shift only tells us the part of an objects full
motion that is directed toward or away from us. (objects radial motion)
• Doppler shifts do not give us any info about how fast an object is moving across
our line of sight. (objects tangential component of motion)
o Rotation Rates:
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