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Doppler Effect the apparent shift in the wavelength of a
wave due to the motion of the source (of the wave) or the
observer.
If the source & observer are approaching , there is a shift to
shorter wavelengths = "blueshift"
If the source & observer are receding , there is a shift to
longer wavelengths = "redshift"
The amount of shift in frequency is precisely dependent on
the speed of approach or recession the "line of sight"
velocity or "radial" velocity.
Astronomers want large telescopes for
increased lightgathering ability
increased angular resolution
Our atmosphere distorts our views of objects in space. The
level of distortion is called the "seeing," and it gives an idea
of the smallest details visible in any telescope.
Astronomers get around limits to seeing by:
put observatories on mountain tops
observe from space or balloons
compensate with "active" control of telescope
Infrared (IR) telescopes detect the "heat" from objects/events in space like dust in clouds, young stars, "cool" objects, etc. Must be done from mountain tops, balloons, & space
Ultraviolet (UV) (must be from space) View hot stars, exploded stars, energetic events
Xray & Gammaray (must be from space) View very highenergy events, very hot stars & gas
By observing the universe at all wavelengths, we can learn much more about objects in space than we could just from one part of the spectrum.
Ch 4 Light & Other EM Radiation
Blackbody Radiation An object at a uniform temperature emits EM waves over a range of wavelengths in a particular way we callblackbody radiation. The intensity of a particular wavelength depends on the temperature of the object. With higher temperature: more energy is emitted at all wavelengths the most intense radiation is emitted at shorter wavelengths
By looking at an object's color, we can tell its temperature.
Temperature scale: We'll use the "kelvin" temperature scale. It's basically the celsius scale set to start "zero" at absolute zero instead of at the freezing point of water. water freezes at 273 K, boils at 373 K
Formation of Spectral Lines
Electrons (e's) orbit the nucleus of the atom (where the
protons [p+] and neutrons [n°] reside) in orbits with specific
energy. These orbits are distinct, there are limited number
of them in a particular element's atoms, and so the e's only
have a few specific energies available to them. As e's
change orbits, they release or absorb a single photon with a
specific energy, and, hence, specific wavelength/color.
emission line spectrum
absorption line spectrum
Each element has its own unique orbits for the e's since
each element's atoms have a specific # of p+'s in the
nucleus. Thus, each element has a unique
emission/absorption spectrum.
Formation of the Solar System
The Earth & planets formedwith the Sun out of a collapsing cloud of gas and (just a tiny bit) of dust. The gas is 3/4 H and 1/4 He, accounting for 99% of the mass.
As the cloud collapsed, the central region became very compressed an hot > the Sun.
Other material farther out "fell" or formed into a rotating disk.
Heat from the Sun drives the lighter gas out to the outer parts of the disk, leaving the small fraction of dust in the inner regions. Over a few 100 million years the dust/ice accumulates into small objects"planetesimals"a few kilometers across.
The planetesimals build into larger objects capable of growing larger by collision ("accretion") and by gravitational attraction. The larger object grow larger by "gobbling up" smaller planetesimals. At stage we call the bigger object "protoplanets."
In the outer part of the disk, the planetismals and protoplanets also grow from collecting the gas (and there's a lot more gas), forming large, gaseous planets.
We can divide the 8 planets into 2 groups.
The terrestrial planets Mercury, Venus, Earth, Mars are
close to the Sun, small, dense, rocky, rotate slowly, have few
moons, no rings...
The jovian planets Jupiter, Saturn, Uranus, Neptune are
far from the Sun, large, lowdensity, gassy/liquid, rotate
rapidly, have many moons & rings...
(Pluto doesn't fit in either group.)
Title: May 14 12:27 PM (13 of 13)
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