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November 21 and 23 Lecture Notes.docx

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John Lester

November 21 st November 23rd 2012 Astronomy Lecture Notes Monday’s Lecture:  Jupiter’s moon Europa: fresh surface of Ice w/ cracks o Tidally heated water below the ice.  Ganymede: surface has two ages.  Callisto: dark, cratered, old surface.  Distance from Jupiter  Systematic change.  Saturn’s moon Titan: dense atmosphere of N2 w/ lakes of methane and ethane.  Medium-sized moons have surprising geology.  All Jovian planets have rings.  Saturn’s rings = not solid but consist of billions of objects from 10M to dust size in orbits. Composition of the Rings:  Use Kirchhoff’s 3 law again: o Observe the spectrum of sunlight reflected by rings  compare spectrum coming from sun  any extra absorption = due to rings  match to samples of Earth. Conclusion: rings are mostly chunks of ice  Dust and Rocks What causes the Rings?  All Jovian planets have large families of moons (small/medium) made of rocks and ice.  These satellites = crowded together.  Because ice is brittle and fragile the satellites fragment when they collide.  Jovian planets have powerful gravities.  Tides pull apart the fragments into rings. Chapter 9: Asteroids. Comets & Dwarf Planets:  Solar Systems smaller objects are different that major planets: o Asteroids  minor planets. o Meteoroids o Comets o Dwarf Planets (2006) What are Asteroids? - “Aster” = star; “oid” = body – an object that looks like a star but it orbits the sun.  Largest = now known = 1000 km in diameter  Smallest detectable = 100 m.  More than 40,000 cataloged asteroids but many more detected.  Probably more than 1 mill. What are the asteroids?  Most asteroids orbit between Mars + Jupiter  “asteroid belt” November 21 st November 23rd 2012 Astronomy Lecture Notes o Jupiter’s powerful gravity controls the spacing.  Some asteroids that are in Jupiter’s orbit o Located ahead of and following Jupiter’s orbit. o These are captured by gravity of Jupiter and Sun.  Some asteroids have elliptical orbits o Orbit close to sun and beyond Jupiter. What are Meteoroids?  Meteoroids are tiny asteroids, too small to detect beyond Earth  size = m = dust.  Meteoroids travel at 30 km  like Earth.  If one hits Earth’s atmosphere: o Heats up from frication. o It gives off light that disintegrates called a meteor of shooting star. - If it is large enough to survive and reach the ground it is called at meteorites = sample of solar system matter that comes to us. Two Families of Meteorites:  “Primitive” meteorites – the matter is just clumped together.  No signs of having reacted.  “Processed” meteorites – the matter has been heated – has been not enough to melt the pure metal, mostly iron. The distinctive pattern required gradual cooling over million of years inside a large asteroids that broke apart. What are comets?  Means “hairy star”.  Orbits = elliptical – going from near the sun out to the edge of the solar system.  Comets are “dirty snowballs” mostly of “ice” = frozen water and gases + small amount of dust, grit, sand and pebbles.  As comet nears the sun, it heats u
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