AST 109 - Lesson 15
How do we do a spectral analysis?
By taking the focused image of light from in a telescope and passing it through a prism or a grating which gives us a spectrum.
Where have we seen ions?
Comet tails
What is an electron?
Negatively charged particles, orbit around the nucleus, have almost no mass.
What charge does an atom have if the # of protons = the # of electrons?
Neutral charge
What did Bohr say about electron orbits?
"Only certain energy levels allowed" in an atom. This is accurate
What is the bright line spectrum?
Dark gaps between bright lines
What is light scattered by gas dependent on?
Density, temperature, elements of cloud, parts of continuum lost lots
What is the biggest lie in this course?
That electron orbits are well-defined and show pictures.
What must a photon have?
The exact energy difference of two orbits
What does the number of neutrons determine?
The isotope
What is an example of black body radiation?
The sun
What does spectrum mean?
to break up light into colors
What is the spectra continuum?
- Smooth intensity curve, no 'dropouts' or spikes -intensity depends on ...., varies smoothly -from dense, hot objects
Absorption spectrum of a star
-Atmosphere of star cooler than surface, so acts like 'cloud' -absorption lines of atmosphere - in continuum from surface -we tell temperature and makeup of atmosphere
Emission spectrum from a cloud
-If low density cloud heated by nearby star(s), it will radiate for us to see -Radiation at well-defined wavelengths, depending on elements present
Blue hot color means what temperature?
10000 K or hotter; the bluer, the hotter; blue hot = white hot
Red hot color means what temperature?
2000-4000 K
What is a neutron?
A particle that has no charge and that is inside the nucleus of an atom
What do we use to find a spectrum?
A spectrograph
Ions are charged atoms. How can this be?
An ion has fewer electrons than protons
What is an isotope?
Atoms of the same element (same # of protons) that have different numbers of neutrons.
How is an element determined?
By the number of protons
What do electrons do as photons come and go?
Change orbits (energies)
What kind of information does a spectrograph give us?
Chemistry - elements present, amounts Motions - spectral lines shifted Temperatures - lines present or absent Masses Ages (with computer modeling)
What situation would give you an absorption spectrum?
Cool, thin gas between you and light source
What is absorption?
Electron gains photon's energy, jumps to higher orbit
What is emission?
Electron loses energy - drops to lower orbit
What situation would give you an continuum spectrum?
Hot, dense gas as your light source
What situation would give you an emission spectrum?
Hot, thin gas to side from light source
How is light scattered by gas?
Light from star scattered/absorbed passing through gas/dust cloud. Dark lines formed = absorption lines
What charges attract and what repel?
Opposites attract and likes repel
Photon Energies
Planck's law - longer wavelength = lower energy
What is a proton?
Positively charged particle found in the nucleus of an atom
What is an atom?
Smallest components of element with characteristics of that elements; consists of a nucleus, protons, neutrons, and electrons
Beyond imaging, what type of analysis do we want to do?
Spectral analysis of a star, cloud, or galaxy
What is black body radiation?
The radiation emitted by a perfect black body; black at all wavelengths -radiates when hot -continuum shape only depends on temperature
What does the number of protons determine?
The type of element
Wien's Displacement Law
The wavelength of peak emission from a black body is inversely proportional to the absolute (kelvin) temperature of the body. -Temp increase = peak moves to shorter wavelengths -Ymax is wavelength of peak of black body continuum
What is a molecule?
Two or more atoms linked together by sharing electrons
Electron orbits are..
Very fuzzy with a cloud around the nucleus
What color and temperature is the sun?
Yellow/green hot, 6000 K
What are ions?
charged atoms that have gained or lost electrons; never are neutrally charged; # of protons does not = # of electrons. extra or missing electrons, atoms are negative or positive
What is the ideal "black body"?
perfectly absorbing
