1	"The Electromagnetic Spectrum," The Electromagnetic Spectrum, Light, Astronomical Tools
2	Light and Other Forms of Radiation The Electromagnetic Spectrum
3	Light as a Wave Light waves are characterized by a wavelength l and a frequency f.
4	Wavelengths and Colors Different colors of visible light correspond to different wavelengths.
5	Dark Side of the Moon “There is no dark side really. It’s all dark.” -- Pink Floyd
6	Dark Side of the Moon What is wrong with this picture? Front: Not all primary colors (eg, pink, magenta), also refraction angles inconsistent Back: Spectrum is Convergent – I think done for art’s sake
7	Light as a Wave Wavelengths of light are measured in units of nanometers (nm) or angstrom (Å):
8	The Electromagnetic Spectrum
9	Light as Particles Light can also appear as particles, called photons (explains, e.g., photoelectric effect). A photon has a specific energy E, proportional to the frequency f:
10	Why is energy per photon so important? Real life example: Ultra-Violet light hitting your skin (important in Laramie!) Threshold for chemical damage set by energy (wavelength) of photons Below threshold (long wavelengths) energy too weak to cause chemical changes Above threshold (short wavelength) energy photons can break apart DNA molecules Number of molecules damaged = number of photons above threshold Very unlikely two photons can hit exactly together to cause damage
11	Temperature and Heat Thermal energy is “kinetic energy” of moving atoms and molecules Hot material energy has more energy available which can be used for Chemical reactions Nuclear reactions (at very high temperature) Escape of gasses from planetary atmospheres Creation of light Collision bumps electron up to higher energy orbit It emits extra energy as light when it drops back down to lower energy orbit (Reverse can happen in absorption of light)
12	Temperature Scales Want temperature scale with energy proportional to T Celsius scale is “arbitrary” (Fahrenheit even more so) 0^o C = freezing point of water 100^o C = boiling point of water By experiment, available energy = 0 at “Absolute Zero” = –273^oC (-459.7^oF) Define “Kelvin” scale with same step size as Celsius, but 0K = -273^oC = Absolute Zero Use Kelvin Scale for most astronomy work Available energy is proportional to T, making equations simple (really! OK, simpler) 273K = freezing point of water 373K = boiling point of water 300K approximately room temperature
13	Planck “Black Body Radiation” Hot objects glow (emit light) as seen in PREDATOR, SSC Video, etc. Heat (and collisions) in material causes electrons to jump to high energy orbits, and as electrons drop back down, some of energy is emitted as light. Reason for name “Black Body Radiation” In a “solid” body the close packing of the atoms means than the electron orbits are complicated, and virtually all energy orbits are allowed. So all wavelengths of light can be emitted or absorbed. A black material is one which readily absorbs all wavelengths of light. These turn out to be the same materials which also readily emit all wavelengths when hot. The hotter the material the more energy it emits as light As you heat up a filament or branding iron, it glows brighter and brighter The hotter the material the more readily it emits high energy (blue) photons As you heat up a filament or branding iron, it first glows dull red, then bright red, then orange, then if you continue, yellow, and eventually blue
14	Planck and other Formulae Planck formula gives intensity of light at each wavelength It is complicated. We’ll use two simpler formulae which can be derived from it. Wien’s law tells us what wavelength has maximum intensity Stefan-Boltzmann law tells us total radiated energy per unit area
15	Example of Wien’s law What is wavelength at which you glow? Room T = 300 K so This wavelength is about 20 times longer than what your eye can see. Thermal camera operates at 7-14 μm. What is temperature of the sun – which has maximum intensity at roughly 0.5 mm?
16	Kirchoff’s laws Hot solids emit continuous spectra Hot gasses try to do this, but can only emit discrete wavelengths Cold gasses try to absorb these same discrete wavelengths
17	Atoms – Electron Configuration Molecules: Multiple atoms sharing/exchanging electrons (H₂O, CH₄) Ions: Single atoms where one or more electrons have escaped (H⁺⁾ Binding energy: Energy needed to let electron escape Permitted “orbits” or energy levels From quantum mechanics, only certain “orbits” are allowed Ground State: Atom with electron in lowest energy orbit Excited State: Atom with at least one atom in a higher energy orbit Transition: As electron jumps from one energy level orbit to another, atom must release/absorb energy different, usually as light. Because only certain orbits are allowed, only certain energy jumps are allowed, and atoms can absorb or emit only certain energies (wavelengths) of light. In complicated molecules or “solids” many transitions are allowed Can use energy levels to “fingerprint” elements and estimate temperatures.
18	Hydrogen Lines Energy absorbed/emitted depends on upper and lower levels Higher energy levels are close together Above a certain energy, electron can escape (ionization) Series of lines named for bottom level To get absorption, lower level must be occupied Depends upon temperature of atoms To get emission, upper level must be occupied Can get down-ward cascade through many levels
19	Astronomical Telescopes
20	Refracting / Reflecting Telescopes
21	Secondary Optics
22	Disadvantages of Refracting Telescopes
23	The Powers of a Telescope: Size does matter!
24	The Powers of a Telescope (II)
25	Seeing
26	The Powers of a Telescope (III) 3. Magnifying Power = ability of the telescope to make the image appear bigger.
27	The Best Location for a Telescope
28	The Best Location for a Telescope (II)
29	Traditional Telescopes (I)
30	Traditional Telescopes (II)
31	Advances in Modern Telescope Design
32	Adaptive Optics
33	Examples of Modern Telescope Design
34	Interferometry
35	CCD Imaging
36	The Spectrograph
37	Radio Astronomy
38	Radio Telescopes
39	Radio Interferometry
40	The Largest Radio Telescopes
41	Science of Radio Astronomy
42	Infrared Astronomy
43	Infrared Telescopes
44	Ultraviolet Astronomy Ultraviolet radiation with l < 290 nm is completely absorbed in the ozone layer of the atmosphere.
45	NASA’s Great Observatories in Space (I)
46	Hubble Space Telescope Images
47	NASA’s Great Observatories in Space (II)
48	NASA’s Great Observatories in Space (III) The Chandra X-ray Telescope
49	Chandra X-ray Observatory
50	The Highest Tech Mirrors Ever! Chandra is the first X-ray telescope to have image as sharp as optical telescopes.
51	NASA’s Great Observatories in Space (IV)
52	Spitzer Space Telescope Images
53	Spitzer Space Telescope Discovered by a Wyoming grad student and professor. The “Cowboy Cluster” – an overlooked Globular Cluster.
54	Kepler’s Supernova with all three of NASA’s Great Observatories Just 400 years ago: (Oct. 9, 1604) Then a bright, naked eye object (no telescopes) It’s still blowing up – now 14 light years wide and expanding at 4 million mph. There’s material there at MANY temperatures, so many wavelengths are needed to understand it.
55	A Multiwavelength Look at Cygnus A A merger-product, and powerful radio galaxy.
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57	The Future of Space-Based Optical/Infrared Astronomy:
58	Terrestrial Planet Finder