Lectures+8+-+12

**__Lecture #8: "Received from Above"__**

 * Electromagnetic Radiation = light (radio, microwave, infrared, visible, ultraviolet, x-ray and gamma)
 * White light is made up of the seven colours of the rainbow: red, orange, yellow, green, blue, indigo and violet.
 * The three primary colours of light are red, green and blue.
 * Refraction is the bending of the direction that light travels at the point where light travels from one clear medium into another clear medium.
 * Light has wave properties
 * The length of the wave, "wavelength" is measured from peak to peak (crest to crest) or trough to trough.
 * The wavelength is variable and for visible light, is from 400nm (violet light) through to 700 nm (red light).
 * Infrared (IR) light is known as heat and while we can't see it, our bodies react to it.
 * Ultraviolet (UV) light also makes our bodies react...we get sunburns, sun tans and skin cancers from to much UV exposure.
 * The atmosphere absorbs most types of light from celestial sources: Only a bit of IR and UV makes it through; no x-ray or gamma light come through; al visible light and radio light make it to the surface of the Earth.
 * The Doppler shift/effect results when there is relative motion of the source of light and the receiver. Wave fronts are compressed when objects move closer to one another ("blueshifting") and stretched when moving away from one another ("redshifting.")
 * __Weblinks__: **
 * An interesting article on the history and how light "works" from the HowStuffWorks.com pages.
 * Electromagnetic radiation as told by the excellent pages at the Lawrence Livermore National Laboratories. Follow the links around these pages to learn a lot!

__Lecture #9: "Tools of the Trade"__

 * Optics are the internal components of telescopes.
 * Telescopes are used by astronomers to brighten the view of images observed, to resolve fine details of those images, and to magnify those images. This last point, the magnification, is not important to professional astronomers, who rarely "look" at what they observe.
 * There are two types of telescopes: refractors, which use lenses and reflectors, which use mirrors. Both types of telescope produce an inverted image of the object viewed.
 * Because of chromatic aberration (the differing refracting angles and the different focal lengths of different colours of light), professional astronomers use reflectors.
 * __Weblink____s__:**
 * How telescopes work, as told by the good folks at the University of Illinois.
 * Wikipedia's telescope pages.
 * How spherical mirrors & parabolic mirrors reflect light (youTube video).
 * Telescopes are housed in Observatories.

__Lecture #10: "Earth, a model Terrestrial Planet"__

 * The interior of the Earth is divided: Inner core, outer core, mantle, crust. The interior is still hot (from the Earth's formation). There is also the oceans and atmosphere.
 * The rotation and convection in the outer core drives the dynamo effect, which generates the Earth's magnetic field.
 * The convection of the fluid mantle drives plate tectonics.
 * Plate tectonics is the movements of Earth's crustal plates. The continental plates are less dense and so float on top of the oceanic plates. Earthquakes result when crustal plates interact.
 * The Oceans absorb condensed when the primordial atmosphere cooled. It absorbs CO_2, and water is essential for life.
 * The atmosphere is primarily N_2, with some O_2 and a bit of Argon. Trace amounts of CO_2 and methane are potent greenhouse gases.
 * The greenhouse effect describes how some gases are transparent to visible light (they let the sunlight in) but opaque to infrared light (they don't let the heat escape to outer space). This heating up of the atmosphere and Earth warms the entire globe. This is the cause of global warming.
 * __Weblink____s__:**
 * The Khan Academy has reorganized and all the Earth Science stuff is located in one spot. Check the videos out, they're great!
 * __Magnetic Fields__: The dynamo effect is the theory that seeks to explain how planet wide magnetic fields form.
 * Cross sectional images of the interior of the Earth are very informative, especially those that show how the seismic waves propagate through the Earth.
 * Heat release from the core drives both plate tectonics (see above section) and the dynamo that produces the magnetic field.
 * Plate Tectonics: The Earth's crust is divided into plates that move on the convecting mantle.
 * The atmosphere acts as a shield for the Earth, absorbing types of radiation that would be harmful to animals (notice the numbers are a bit different from those I gave in class...I've checked, different websites show slightly different concentrations. So "approximately," is a good way to describe how much nitrogen is in the atmosphere, for example.)
 * The Oceans can absorb CO_2 in a complicated, but fascinating way. Our oceans have evolved over the eons, and a brief summary is followed by more details about the (questionable) extra-terrestrial origins of water.
 * __Greenhouse Effect__: Visible light from the Sun in through the Earth's atmosphere heats up the land and the resulting infrared radiation cannot escape because of the "greenhouse" gases (eg. CO_2) in the atmosphere. Best told with the help of images.

__Lecture #11: "Mercury & Venus"__

 * Mercury
 * Mercury is smaller than the Earth, much less massive than the Earth, about the same density as the Earth, and has much greater temperature variations than the Earth. It is closer to the Sun than the Earth is and has a markedly elliptical orbit.
 * Mercury experiences a spin-orbit resonance, rotating 1.5 times every orbit. Mercury's orbital period is ~88 days.
 * Mercury has a large core, which must have a liquid layer, as Mercury has a weak, planet-wide magnetic field which is (funnily enough) offset from the rotational axis.
 * Two of the major crustal features of Mercury are Caloris Basin and the lobate scarps.
 * Mercury doesn't have a proper atmosphere, but atoms sputtered from the surface comprise an exosphere around the planet.
 * Venus
 * Venus is comparable in size, mass and density to the Earth. The temperature though, is much higher than the Earth's surface temperature. It's elliptical orbit is the most circular of all the planets.
 * A day on Venus (225 Earth days) is shorter than it's year (243 Earth days), and Venus' rotation is "backwards" -- opposite in direction to the other planets. An off-center collision is one hypothesis to explain this anomaly, and interaction of solar tides in the thick Venusian atmosphere is another.
 * The surface of Venus is lacking the large craters that invariably formed during the era of heavy bombardment in the early eons of the solar system. This suggests resurfacing, and one hypothesis is a global resurfacing event hundreds of millions of years ago.
 * Crustal features on Venus include Ishtar Terra, Aphrodite Terra and Maxwell Mons.
 * The atmosphere of Venus is very thick and almost entirely CO_2. This strong greenhouse gas keeps Venus' surface temperature hot...~470oC hot! This shows what a "runaway greenhouse effect" can do to the surface of a planet.
 * Weblinks:**
 * MESSENGER's website at NASA gas a lot of great images and information about Mercury.
 * Wikipedia's Mercury pages are also a treasure trove of information
 * Latest and greatest data on Venus is available at the ESA's Venus Express website.
 * And as usual, wikipedia's Venus site is filled with fascinating stuff too, as is Solarsystem.NASA.gov!

__Lecture #12: "Mars"__

 * To date, there has been no evidence that life has ever existed on Mars.
 * Nevertheless, there have been many, many missions (many failed missions too) to Mars to try to determine what the planet is really like.
 * There was likely once flowing surface water on Mars (evidence includes sedimentary rock, "blueberries" and tear drop shaped islands) but there is no longer water on the surface.
 * One obvious thing stands our: the topographical dichotomy...the southern hemisphere is substantially elevated compared to the northern hemisphere. Also, the southern hemisphere is much more heavily craters. Hypotheses to explain this dichotomy include a single massive impact in the north, and endogenic (interior) processes that could have caused the south to bulge.
 * Mars is small, and so cooled quickly. Theories suggest that Mars' magnetic dynamo ceased after only ~500 million years of existence.
 * Having lost it's magnetic field, there was nothing to protect the atmosphere from solar wind, and over the gigayears, the atmosphere slowly eroded away. With only a very think atmosphere, the surface (and its water) had virtually no protection from the UV radiation. UV radiation can dissociate water molecules and with the gravity as low as it is on Mars, the hydrogen was lost to space. The remaining oxygen reacted with iron in the crust and created the distinctive color or Mars: iron oxide ("rust" here on Earth).
 * __Weblink____s__:**
 * Naturally, wikipedia's Mars pages are extensive.
 * Sedimentary rock on Mars was initial evidence of flowing water.
 * Mars is small, so it's had time to cool off. It used to have a magnetic field, but that was lost when it cooled. Mars lost its atmosphere likely as a result of the loss of it's magnetic field which allowed the sputtering (see linked article) to occur. With no atmosphere (or ozone), the UV radiation (237nm or 123nm, depending on reaction) dissociated the water molecules on Mars surface. The oxygen reacted with the iron in the crustal rock and the hydrogen was lost to space.